Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * procarray.c
4 : * POSTGRES process array code.
5 : *
6 : *
7 : * This module maintains arrays of PGPROC substructures, as well as associated
8 : * arrays in ProcGlobal, for all active backends. Although there are several
9 : * uses for this, the principal one is as a means of determining the set of
10 : * currently running transactions.
11 : *
12 : * Because of various subtle race conditions it is critical that a backend
13 : * hold the correct locks while setting or clearing its xid (in
14 : * ProcGlobal->xids[]/MyProc->xid). See notes in
15 : * src/backend/access/transam/README.
16 : *
17 : * The process arrays now also include structures representing prepared
18 : * transactions. The xid and subxids fields of these are valid, as are the
19 : * myProcLocks lists. They can be distinguished from regular backend PGPROCs
20 : * at need by checking for pid == 0.
21 : *
22 : * During hot standby, we also keep a list of XIDs representing transactions
23 : * that are known to be running on the primary (or more precisely, were running
24 : * as of the current point in the WAL stream). This list is kept in the
25 : * KnownAssignedXids array, and is updated by watching the sequence of
26 : * arriving XIDs. This is necessary because if we leave those XIDs out of
27 : * snapshots taken for standby queries, then they will appear to be already
28 : * complete, leading to MVCC failures. Note that in hot standby, the PGPROC
29 : * array represents standby processes, which by definition are not running
30 : * transactions that have XIDs.
31 : *
32 : * It is perhaps possible for a backend on the primary to terminate without
33 : * writing an abort record for its transaction. While that shouldn't really
34 : * happen, it would tie up KnownAssignedXids indefinitely, so we protect
35 : * ourselves by pruning the array when a valid list of running XIDs arrives.
36 : *
37 : * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
38 : * Portions Copyright (c) 1994, Regents of the University of California
39 : *
40 : *
41 : * IDENTIFICATION
42 : * src/backend/storage/ipc/procarray.c
43 : *
44 : *-------------------------------------------------------------------------
45 : */
46 : #include "postgres.h"
47 :
48 : #include <signal.h>
49 :
50 : #include "access/subtrans.h"
51 : #include "access/transam.h"
52 : #include "access/twophase.h"
53 : #include "access/xact.h"
54 : #include "access/xlogutils.h"
55 : #include "catalog/catalog.h"
56 : #include "catalog/pg_authid.h"
57 : #include "commands/dbcommands.h"
58 : #include "miscadmin.h"
59 : #include "pgstat.h"
60 : #include "port/pg_lfind.h"
61 : #include "storage/proc.h"
62 : #include "storage/procarray.h"
63 : #include "utils/acl.h"
64 : #include "utils/builtins.h"
65 : #include "utils/rel.h"
66 : #include "utils/snapmgr.h"
67 :
68 : #define UINT32_ACCESS_ONCE(var) ((uint32)(*((volatile uint32 *)&(var))))
69 :
70 : /* Our shared memory area */
71 : typedef struct ProcArrayStruct
72 : {
73 : int numProcs; /* number of valid procs entries */
74 : int maxProcs; /* allocated size of procs array */
75 :
76 : /*
77 : * Known assigned XIDs handling
78 : */
79 : int maxKnownAssignedXids; /* allocated size of array */
80 : int numKnownAssignedXids; /* current # of valid entries */
81 : int tailKnownAssignedXids; /* index of oldest valid element */
82 : int headKnownAssignedXids; /* index of newest element, + 1 */
83 :
84 : /*
85 : * Highest subxid that has been removed from KnownAssignedXids array to
86 : * prevent overflow; or InvalidTransactionId if none. We track this for
87 : * similar reasons to tracking overflowing cached subxids in PGPROC
88 : * entries. Must hold exclusive ProcArrayLock to change this, and shared
89 : * lock to read it.
90 : */
91 : TransactionId lastOverflowedXid;
92 :
93 : /* oldest xmin of any replication slot */
94 : TransactionId replication_slot_xmin;
95 : /* oldest catalog xmin of any replication slot */
96 : TransactionId replication_slot_catalog_xmin;
97 :
98 : /* indexes into allProcs[], has PROCARRAY_MAXPROCS entries */
99 : int pgprocnos[FLEXIBLE_ARRAY_MEMBER];
100 : } ProcArrayStruct;
101 :
102 : /*
103 : * State for the GlobalVisTest* family of functions. Those functions can
104 : * e.g. be used to decide if a deleted row can be removed without violating
105 : * MVCC semantics: If the deleted row's xmax is not considered to be running
106 : * by anyone, the row can be removed.
107 : *
108 : * To avoid slowing down GetSnapshotData(), we don't calculate a precise
109 : * cutoff XID while building a snapshot (looking at the frequently changing
110 : * xmins scales badly). Instead we compute two boundaries while building the
111 : * snapshot:
112 : *
113 : * 1) definitely_needed, indicating that rows deleted by XIDs >=
114 : * definitely_needed are definitely still visible.
115 : *
116 : * 2) maybe_needed, indicating that rows deleted by XIDs < maybe_needed can
117 : * definitely be removed
118 : *
119 : * When testing an XID that falls in between the two (i.e. XID >= maybe_needed
120 : * && XID < definitely_needed), the boundaries can be recomputed (using
121 : * ComputeXidHorizons()) to get a more accurate answer. This is cheaper than
122 : * maintaining an accurate value all the time.
123 : *
124 : * As it is not cheap to compute accurate boundaries, we limit the number of
125 : * times that happens in short succession. See GlobalVisTestShouldUpdate().
126 : *
127 : *
128 : * There are three backend lifetime instances of this struct, optimized for
129 : * different types of relations. As e.g. a normal user defined table in one
130 : * database is inaccessible to backends connected to another database, a test
131 : * specific to a relation can be more aggressive than a test for a shared
132 : * relation. Currently we track four different states:
133 : *
134 : * 1) GlobalVisSharedRels, which only considers an XID's
135 : * effects visible-to-everyone if neither snapshots in any database, nor a
136 : * replication slot's xmin, nor a replication slot's catalog_xmin might
137 : * still consider XID as running.
138 : *
139 : * 2) GlobalVisCatalogRels, which only considers an XID's
140 : * effects visible-to-everyone if neither snapshots in the current
141 : * database, nor a replication slot's xmin, nor a replication slot's
142 : * catalog_xmin might still consider XID as running.
143 : *
144 : * I.e. the difference to GlobalVisSharedRels is that
145 : * snapshot in other databases are ignored.
146 : *
147 : * 3) GlobalVisDataRels, which only considers an XID's
148 : * effects visible-to-everyone if neither snapshots in the current
149 : * database, nor a replication slot's xmin consider XID as running.
150 : *
151 : * I.e. the difference to GlobalVisCatalogRels is that
152 : * replication slot's catalog_xmin is not taken into account.
153 : *
154 : * 4) GlobalVisTempRels, which only considers the current session, as temp
155 : * tables are not visible to other sessions.
156 : *
157 : * GlobalVisTestFor(relation) returns the appropriate state
158 : * for the relation.
159 : *
160 : * The boundaries are FullTransactionIds instead of TransactionIds to avoid
161 : * wraparound dangers. There e.g. would otherwise exist no procarray state to
162 : * prevent maybe_needed to become old enough after the GetSnapshotData()
163 : * call.
164 : *
165 : * The typedef is in the header.
166 : */
167 : struct GlobalVisState
168 : {
169 : /* XIDs >= are considered running by some backend */
170 : FullTransactionId definitely_needed;
171 :
172 : /* XIDs < are not considered to be running by any backend */
173 : FullTransactionId maybe_needed;
174 : };
175 :
176 : /*
177 : * Result of ComputeXidHorizons().
178 : */
179 : typedef struct ComputeXidHorizonsResult
180 : {
181 : /*
182 : * The value of TransamVariables->latestCompletedXid when
183 : * ComputeXidHorizons() held ProcArrayLock.
184 : */
185 : FullTransactionId latest_completed;
186 :
187 : /*
188 : * The same for procArray->replication_slot_xmin and
189 : * procArray->replication_slot_catalog_xmin.
190 : */
191 : TransactionId slot_xmin;
192 : TransactionId slot_catalog_xmin;
193 :
194 : /*
195 : * Oldest xid that any backend might still consider running. This needs to
196 : * include processes running VACUUM, in contrast to the normal visibility
197 : * cutoffs, as vacuum needs to be able to perform pg_subtrans lookups when
198 : * determining visibility, but doesn't care about rows above its xmin to
199 : * be removed.
200 : *
201 : * This likely should only be needed to determine whether pg_subtrans can
202 : * be truncated. It currently includes the effects of replication slots,
203 : * for historical reasons. But that could likely be changed.
204 : */
205 : TransactionId oldest_considered_running;
206 :
207 : /*
208 : * Oldest xid for which deleted tuples need to be retained in shared
209 : * tables.
210 : *
211 : * This includes the effects of replication slots. If that's not desired,
212 : * look at shared_oldest_nonremovable_raw;
213 : */
214 : TransactionId shared_oldest_nonremovable;
215 :
216 : /*
217 : * Oldest xid that may be necessary to retain in shared tables. This is
218 : * the same as shared_oldest_nonremovable, except that is not affected by
219 : * replication slot's catalog_xmin.
220 : *
221 : * This is mainly useful to be able to send the catalog_xmin to upstream
222 : * streaming replication servers via hot_standby_feedback, so they can
223 : * apply the limit only when accessing catalog tables.
224 : */
225 : TransactionId shared_oldest_nonremovable_raw;
226 :
227 : /*
228 : * Oldest xid for which deleted tuples need to be retained in non-shared
229 : * catalog tables.
230 : */
231 : TransactionId catalog_oldest_nonremovable;
232 :
233 : /*
234 : * Oldest xid for which deleted tuples need to be retained in normal user
235 : * defined tables.
236 : */
237 : TransactionId data_oldest_nonremovable;
238 :
239 : /*
240 : * Oldest xid for which deleted tuples need to be retained in this
241 : * session's temporary tables.
242 : */
243 : TransactionId temp_oldest_nonremovable;
244 : } ComputeXidHorizonsResult;
245 :
246 : /*
247 : * Return value for GlobalVisHorizonKindForRel().
248 : */
249 : typedef enum GlobalVisHorizonKind
250 : {
251 : VISHORIZON_SHARED,
252 : VISHORIZON_CATALOG,
253 : VISHORIZON_DATA,
254 : VISHORIZON_TEMP,
255 : } GlobalVisHorizonKind;
256 :
257 : /*
258 : * Reason codes for KnownAssignedXidsCompress().
259 : */
260 : typedef enum KAXCompressReason
261 : {
262 : KAX_NO_SPACE, /* need to free up space at array end */
263 : KAX_PRUNE, /* we just pruned old entries */
264 : KAX_TRANSACTION_END, /* we just committed/removed some XIDs */
265 : KAX_STARTUP_PROCESS_IDLE, /* startup process is about to sleep */
266 : } KAXCompressReason;
267 :
268 :
269 : static ProcArrayStruct *procArray;
270 :
271 : static PGPROC *allProcs;
272 :
273 : /*
274 : * Cache to reduce overhead of repeated calls to TransactionIdIsInProgress()
275 : */
276 : static TransactionId cachedXidIsNotInProgress = InvalidTransactionId;
277 :
278 : /*
279 : * Bookkeeping for tracking emulated transactions in recovery
280 : */
281 : static TransactionId *KnownAssignedXids;
282 : static bool *KnownAssignedXidsValid;
283 : static TransactionId latestObservedXid = InvalidTransactionId;
284 :
285 : /*
286 : * If we're in STANDBY_SNAPSHOT_PENDING state, standbySnapshotPendingXmin is
287 : * the highest xid that might still be running that we don't have in
288 : * KnownAssignedXids.
289 : */
290 : static TransactionId standbySnapshotPendingXmin;
291 :
292 : /*
293 : * State for visibility checks on different types of relations. See struct
294 : * GlobalVisState for details. As shared, catalog, normal and temporary
295 : * relations can have different horizons, one such state exists for each.
296 : */
297 : static GlobalVisState GlobalVisSharedRels;
298 : static GlobalVisState GlobalVisCatalogRels;
299 : static GlobalVisState GlobalVisDataRels;
300 : static GlobalVisState GlobalVisTempRels;
301 :
302 : /*
303 : * This backend's RecentXmin at the last time the accurate xmin horizon was
304 : * recomputed, or InvalidTransactionId if it has not. Used to limit how many
305 : * times accurate horizons are recomputed. See GlobalVisTestShouldUpdate().
306 : */
307 : static TransactionId ComputeXidHorizonsResultLastXmin;
308 :
309 : #ifdef XIDCACHE_DEBUG
310 :
311 : /* counters for XidCache measurement */
312 : static long xc_by_recent_xmin = 0;
313 : static long xc_by_known_xact = 0;
314 : static long xc_by_my_xact = 0;
315 : static long xc_by_latest_xid = 0;
316 : static long xc_by_main_xid = 0;
317 : static long xc_by_child_xid = 0;
318 : static long xc_by_known_assigned = 0;
319 : static long xc_no_overflow = 0;
320 : static long xc_slow_answer = 0;
321 :
322 : #define xc_by_recent_xmin_inc() (xc_by_recent_xmin++)
323 : #define xc_by_known_xact_inc() (xc_by_known_xact++)
324 : #define xc_by_my_xact_inc() (xc_by_my_xact++)
325 : #define xc_by_latest_xid_inc() (xc_by_latest_xid++)
326 : #define xc_by_main_xid_inc() (xc_by_main_xid++)
327 : #define xc_by_child_xid_inc() (xc_by_child_xid++)
328 : #define xc_by_known_assigned_inc() (xc_by_known_assigned++)
329 : #define xc_no_overflow_inc() (xc_no_overflow++)
330 : #define xc_slow_answer_inc() (xc_slow_answer++)
331 :
332 : static void DisplayXidCache(void);
333 : #else /* !XIDCACHE_DEBUG */
334 :
335 : #define xc_by_recent_xmin_inc() ((void) 0)
336 : #define xc_by_known_xact_inc() ((void) 0)
337 : #define xc_by_my_xact_inc() ((void) 0)
338 : #define xc_by_latest_xid_inc() ((void) 0)
339 : #define xc_by_main_xid_inc() ((void) 0)
340 : #define xc_by_child_xid_inc() ((void) 0)
341 : #define xc_by_known_assigned_inc() ((void) 0)
342 : #define xc_no_overflow_inc() ((void) 0)
343 : #define xc_slow_answer_inc() ((void) 0)
344 : #endif /* XIDCACHE_DEBUG */
345 :
346 : /* Primitives for KnownAssignedXids array handling for standby */
347 : static void KnownAssignedXidsCompress(KAXCompressReason reason, bool haveLock);
348 : static void KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
349 : bool exclusive_lock);
350 : static bool KnownAssignedXidsSearch(TransactionId xid, bool remove);
351 : static bool KnownAssignedXidExists(TransactionId xid);
352 : static void KnownAssignedXidsRemove(TransactionId xid);
353 : static void KnownAssignedXidsRemoveTree(TransactionId xid, int nsubxids,
354 : TransactionId *subxids);
355 : static void KnownAssignedXidsRemovePreceding(TransactionId removeXid);
356 : static int KnownAssignedXidsGet(TransactionId *xarray, TransactionId xmax);
357 : static int KnownAssignedXidsGetAndSetXmin(TransactionId *xarray,
358 : TransactionId *xmin,
359 : TransactionId xmax);
360 : static TransactionId KnownAssignedXidsGetOldestXmin(void);
361 : static void KnownAssignedXidsDisplay(int trace_level);
362 : static void KnownAssignedXidsReset(void);
363 : static inline void ProcArrayEndTransactionInternal(PGPROC *proc, TransactionId latestXid);
364 : static void ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid);
365 : static void MaintainLatestCompletedXid(TransactionId latestXid);
366 : static void MaintainLatestCompletedXidRecovery(TransactionId latestXid);
367 :
368 : static inline FullTransactionId FullXidRelativeTo(FullTransactionId rel,
369 : TransactionId xid);
370 : static void GlobalVisUpdateApply(ComputeXidHorizonsResult *horizons);
371 :
372 : /*
373 : * Report shared-memory space needed by ProcArrayShmemInit
374 : */
375 : Size
376 3998 : ProcArrayShmemSize(void)
377 : {
378 : Size size;
379 :
380 : /* Size of the ProcArray structure itself */
381 : #define PROCARRAY_MAXPROCS (MaxBackends + max_prepared_xacts)
382 :
383 3998 : size = offsetof(ProcArrayStruct, pgprocnos);
384 3998 : size = add_size(size, mul_size(sizeof(int), PROCARRAY_MAXPROCS));
385 :
386 : /*
387 : * During Hot Standby processing we have a data structure called
388 : * KnownAssignedXids, created in shared memory. Local data structures are
389 : * also created in various backends during GetSnapshotData(),
390 : * TransactionIdIsInProgress() and GetRunningTransactionData(). All of the
391 : * main structures created in those functions must be identically sized,
392 : * since we may at times copy the whole of the data structures around. We
393 : * refer to this size as TOTAL_MAX_CACHED_SUBXIDS.
394 : *
395 : * Ideally we'd only create this structure if we were actually doing hot
396 : * standby in the current run, but we don't know that yet at the time
397 : * shared memory is being set up.
398 : */
399 : #define TOTAL_MAX_CACHED_SUBXIDS \
400 : ((PGPROC_MAX_CACHED_SUBXIDS + 1) * PROCARRAY_MAXPROCS)
401 :
402 3998 : if (EnableHotStandby)
403 : {
404 3974 : size = add_size(size,
405 : mul_size(sizeof(TransactionId),
406 3974 : TOTAL_MAX_CACHED_SUBXIDS));
407 3974 : size = add_size(size,
408 3974 : mul_size(sizeof(bool), TOTAL_MAX_CACHED_SUBXIDS));
409 : }
410 :
411 3998 : return size;
412 : }
413 :
414 : /*
415 : * Initialize the shared PGPROC array during postmaster startup.
416 : */
417 : void
418 2152 : ProcArrayShmemInit(void)
419 : {
420 : bool found;
421 :
422 : /* Create or attach to the ProcArray shared structure */
423 2152 : procArray = (ProcArrayStruct *)
424 2152 : ShmemInitStruct("Proc Array",
425 : add_size(offsetof(ProcArrayStruct, pgprocnos),
426 : mul_size(sizeof(int),
427 2152 : PROCARRAY_MAXPROCS)),
428 : &found);
429 :
430 2152 : if (!found)
431 : {
432 : /*
433 : * We're the first - initialize.
434 : */
435 2152 : procArray->numProcs = 0;
436 2152 : procArray->maxProcs = PROCARRAY_MAXPROCS;
437 2152 : procArray->maxKnownAssignedXids = TOTAL_MAX_CACHED_SUBXIDS;
438 2152 : procArray->numKnownAssignedXids = 0;
439 2152 : procArray->tailKnownAssignedXids = 0;
440 2152 : procArray->headKnownAssignedXids = 0;
441 2152 : procArray->lastOverflowedXid = InvalidTransactionId;
442 2152 : procArray->replication_slot_xmin = InvalidTransactionId;
443 2152 : procArray->replication_slot_catalog_xmin = InvalidTransactionId;
444 2152 : TransamVariables->xactCompletionCount = 1;
445 : }
446 :
447 2152 : allProcs = ProcGlobal->allProcs;
448 :
449 : /* Create or attach to the KnownAssignedXids arrays too, if needed */
450 2152 : if (EnableHotStandby)
451 : {
452 2140 : KnownAssignedXids = (TransactionId *)
453 2140 : ShmemInitStruct("KnownAssignedXids",
454 : mul_size(sizeof(TransactionId),
455 2140 : TOTAL_MAX_CACHED_SUBXIDS),
456 : &found);
457 2140 : KnownAssignedXidsValid = (bool *)
458 2140 : ShmemInitStruct("KnownAssignedXidsValid",
459 2140 : mul_size(sizeof(bool), TOTAL_MAX_CACHED_SUBXIDS),
460 : &found);
461 : }
462 2152 : }
463 :
464 : /*
465 : * Add the specified PGPROC to the shared array.
466 : */
467 : void
468 34888 : ProcArrayAdd(PGPROC *proc)
469 : {
470 34888 : int pgprocno = GetNumberFromPGProc(proc);
471 34888 : ProcArrayStruct *arrayP = procArray;
472 : int index;
473 : int movecount;
474 :
475 : /* See ProcGlobal comment explaining why both locks are held */
476 34888 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
477 34888 : LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
478 :
479 34888 : if (arrayP->numProcs >= arrayP->maxProcs)
480 : {
481 : /*
482 : * Oops, no room. (This really shouldn't happen, since there is a
483 : * fixed supply of PGPROC structs too, and so we should have failed
484 : * earlier.)
485 : */
486 0 : ereport(FATAL,
487 : (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
488 : errmsg("sorry, too many clients already")));
489 : }
490 :
491 : /*
492 : * Keep the procs array sorted by (PGPROC *) so that we can utilize
493 : * locality of references much better. This is useful while traversing the
494 : * ProcArray because there is an increased likelihood of finding the next
495 : * PGPROC structure in the cache.
496 : *
497 : * Since the occurrence of adding/removing a proc is much lower than the
498 : * access to the ProcArray itself, the overhead should be marginal
499 : */
500 83108 : for (index = 0; index < arrayP->numProcs; index++)
501 : {
502 75068 : int this_procno = arrayP->pgprocnos[index];
503 :
504 : Assert(this_procno >= 0 && this_procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
505 : Assert(allProcs[this_procno].pgxactoff == index);
506 :
507 : /* If we have found our right position in the array, break */
508 75068 : if (this_procno > pgprocno)
509 26848 : break;
510 : }
511 :
512 34888 : movecount = arrayP->numProcs - index;
513 34888 : memmove(&arrayP->pgprocnos[index + 1],
514 34888 : &arrayP->pgprocnos[index],
515 : movecount * sizeof(*arrayP->pgprocnos));
516 34888 : memmove(&ProcGlobal->xids[index + 1],
517 34888 : &ProcGlobal->xids[index],
518 : movecount * sizeof(*ProcGlobal->xids));
519 34888 : memmove(&ProcGlobal->subxidStates[index + 1],
520 34888 : &ProcGlobal->subxidStates[index],
521 : movecount * sizeof(*ProcGlobal->subxidStates));
522 34888 : memmove(&ProcGlobal->statusFlags[index + 1],
523 34888 : &ProcGlobal->statusFlags[index],
524 : movecount * sizeof(*ProcGlobal->statusFlags));
525 :
526 34888 : arrayP->pgprocnos[index] = GetNumberFromPGProc(proc);
527 34888 : proc->pgxactoff = index;
528 34888 : ProcGlobal->xids[index] = proc->xid;
529 34888 : ProcGlobal->subxidStates[index] = proc->subxidStatus;
530 34888 : ProcGlobal->statusFlags[index] = proc->statusFlags;
531 :
532 34888 : arrayP->numProcs++;
533 :
534 : /* adjust pgxactoff for all following PGPROCs */
535 34888 : index++;
536 96824 : for (; index < arrayP->numProcs; index++)
537 : {
538 61936 : int procno = arrayP->pgprocnos[index];
539 :
540 : Assert(procno >= 0 && procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
541 : Assert(allProcs[procno].pgxactoff == index - 1);
542 :
543 61936 : allProcs[procno].pgxactoff = index;
544 : }
545 :
546 : /*
547 : * Release in reversed acquisition order, to reduce frequency of having to
548 : * wait for XidGenLock while holding ProcArrayLock.
549 : */
550 34888 : LWLockRelease(XidGenLock);
551 34888 : LWLockRelease(ProcArrayLock);
552 34888 : }
553 :
554 : /*
555 : * Remove the specified PGPROC from the shared array.
556 : *
557 : * When latestXid is a valid XID, we are removing a live 2PC gxact from the
558 : * array, and thus causing it to appear as "not running" anymore. In this
559 : * case we must advance latestCompletedXid. (This is essentially the same
560 : * as ProcArrayEndTransaction followed by removal of the PGPROC, but we take
561 : * the ProcArrayLock only once, and don't damage the content of the PGPROC;
562 : * twophase.c depends on the latter.)
563 : */
564 : void
565 34836 : ProcArrayRemove(PGPROC *proc, TransactionId latestXid)
566 : {
567 34836 : ProcArrayStruct *arrayP = procArray;
568 : int myoff;
569 : int movecount;
570 :
571 : #ifdef XIDCACHE_DEBUG
572 : /* dump stats at backend shutdown, but not prepared-xact end */
573 : if (proc->pid != 0)
574 : DisplayXidCache();
575 : #endif
576 :
577 : /* See ProcGlobal comment explaining why both locks are held */
578 34836 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
579 34836 : LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
580 :
581 34836 : myoff = proc->pgxactoff;
582 :
583 : Assert(myoff >= 0 && myoff < arrayP->numProcs);
584 : Assert(ProcGlobal->allProcs[arrayP->pgprocnos[myoff]].pgxactoff == myoff);
585 :
586 34836 : if (TransactionIdIsValid(latestXid))
587 : {
588 : Assert(TransactionIdIsValid(ProcGlobal->xids[myoff]));
589 :
590 : /* Advance global latestCompletedXid while holding the lock */
591 590 : MaintainLatestCompletedXid(latestXid);
592 :
593 : /* Same with xactCompletionCount */
594 590 : TransamVariables->xactCompletionCount++;
595 :
596 590 : ProcGlobal->xids[myoff] = InvalidTransactionId;
597 590 : ProcGlobal->subxidStates[myoff].overflowed = false;
598 590 : ProcGlobal->subxidStates[myoff].count = 0;
599 : }
600 : else
601 : {
602 : /* Shouldn't be trying to remove a live transaction here */
603 : Assert(!TransactionIdIsValid(ProcGlobal->xids[myoff]));
604 : }
605 :
606 : Assert(!TransactionIdIsValid(ProcGlobal->xids[myoff]));
607 : Assert(ProcGlobal->subxidStates[myoff].count == 0);
608 : Assert(ProcGlobal->subxidStates[myoff].overflowed == false);
609 :
610 34836 : ProcGlobal->statusFlags[myoff] = 0;
611 :
612 : /* Keep the PGPROC array sorted. See notes above */
613 34836 : movecount = arrayP->numProcs - myoff - 1;
614 34836 : memmove(&arrayP->pgprocnos[myoff],
615 34836 : &arrayP->pgprocnos[myoff + 1],
616 : movecount * sizeof(*arrayP->pgprocnos));
617 34836 : memmove(&ProcGlobal->xids[myoff],
618 34836 : &ProcGlobal->xids[myoff + 1],
619 : movecount * sizeof(*ProcGlobal->xids));
620 34836 : memmove(&ProcGlobal->subxidStates[myoff],
621 34836 : &ProcGlobal->subxidStates[myoff + 1],
622 : movecount * sizeof(*ProcGlobal->subxidStates));
623 34836 : memmove(&ProcGlobal->statusFlags[myoff],
624 34836 : &ProcGlobal->statusFlags[myoff + 1],
625 : movecount * sizeof(*ProcGlobal->statusFlags));
626 :
627 34836 : arrayP->pgprocnos[arrayP->numProcs - 1] = -1; /* for debugging */
628 34836 : arrayP->numProcs--;
629 :
630 : /*
631 : * Adjust pgxactoff of following procs for removed PGPROC (note that
632 : * numProcs already has been decremented).
633 : */
634 102146 : for (int index = myoff; index < arrayP->numProcs; index++)
635 : {
636 67310 : int procno = arrayP->pgprocnos[index];
637 :
638 : Assert(procno >= 0 && procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
639 : Assert(allProcs[procno].pgxactoff - 1 == index);
640 :
641 67310 : allProcs[procno].pgxactoff = index;
642 : }
643 :
644 : /*
645 : * Release in reversed acquisition order, to reduce frequency of having to
646 : * wait for XidGenLock while holding ProcArrayLock.
647 : */
648 34836 : LWLockRelease(XidGenLock);
649 34836 : LWLockRelease(ProcArrayLock);
650 34836 : }
651 :
652 :
653 : /*
654 : * ProcArrayEndTransaction -- mark a transaction as no longer running
655 : *
656 : * This is used interchangeably for commit and abort cases. The transaction
657 : * commit/abort must already be reported to WAL and pg_xact.
658 : *
659 : * proc is currently always MyProc, but we pass it explicitly for flexibility.
660 : * latestXid is the latest Xid among the transaction's main XID and
661 : * subtransactions, or InvalidTransactionId if it has no XID. (We must ask
662 : * the caller to pass latestXid, instead of computing it from the PGPROC's
663 : * contents, because the subxid information in the PGPROC might be
664 : * incomplete.)
665 : */
666 : void
667 1096324 : ProcArrayEndTransaction(PGPROC *proc, TransactionId latestXid)
668 : {
669 1096324 : if (TransactionIdIsValid(latestXid))
670 : {
671 : /*
672 : * We must lock ProcArrayLock while clearing our advertised XID, so
673 : * that we do not exit the set of "running" transactions while someone
674 : * else is taking a snapshot. See discussion in
675 : * src/backend/access/transam/README.
676 : */
677 : Assert(TransactionIdIsValid(proc->xid));
678 :
679 : /*
680 : * If we can immediately acquire ProcArrayLock, we clear our own XID
681 : * and release the lock. If not, use group XID clearing to improve
682 : * efficiency.
683 : */
684 265998 : if (LWLockConditionalAcquire(ProcArrayLock, LW_EXCLUSIVE))
685 : {
686 265712 : ProcArrayEndTransactionInternal(proc, latestXid);
687 265712 : LWLockRelease(ProcArrayLock);
688 : }
689 : else
690 286 : ProcArrayGroupClearXid(proc, latestXid);
691 : }
692 : else
693 : {
694 : /*
695 : * If we have no XID, we don't need to lock, since we won't affect
696 : * anyone else's calculation of a snapshot. We might change their
697 : * estimate of global xmin, but that's OK.
698 : */
699 : Assert(!TransactionIdIsValid(proc->xid));
700 : Assert(proc->subxidStatus.count == 0);
701 : Assert(!proc->subxidStatus.overflowed);
702 :
703 830326 : proc->vxid.lxid = InvalidLocalTransactionId;
704 830326 : proc->xmin = InvalidTransactionId;
705 :
706 : /* be sure this is cleared in abort */
707 830326 : proc->delayChkptFlags = 0;
708 :
709 830326 : proc->recoveryConflictPending = false;
710 :
711 : /* must be cleared with xid/xmin: */
712 : /* avoid unnecessarily dirtying shared cachelines */
713 830326 : if (proc->statusFlags & PROC_VACUUM_STATE_MASK)
714 : {
715 : Assert(!LWLockHeldByMe(ProcArrayLock));
716 242730 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
717 : Assert(proc->statusFlags == ProcGlobal->statusFlags[proc->pgxactoff]);
718 242730 : proc->statusFlags &= ~PROC_VACUUM_STATE_MASK;
719 242730 : ProcGlobal->statusFlags[proc->pgxactoff] = proc->statusFlags;
720 242730 : LWLockRelease(ProcArrayLock);
721 : }
722 : }
723 1096324 : }
724 :
725 : /*
726 : * Mark a write transaction as no longer running.
727 : *
728 : * We don't do any locking here; caller must handle that.
729 : */
730 : static inline void
731 265998 : ProcArrayEndTransactionInternal(PGPROC *proc, TransactionId latestXid)
732 : {
733 265998 : int pgxactoff = proc->pgxactoff;
734 :
735 : /*
736 : * Note: we need exclusive lock here because we're going to change other
737 : * processes' PGPROC entries.
738 : */
739 : Assert(LWLockHeldByMeInMode(ProcArrayLock, LW_EXCLUSIVE));
740 : Assert(TransactionIdIsValid(ProcGlobal->xids[pgxactoff]));
741 : Assert(ProcGlobal->xids[pgxactoff] == proc->xid);
742 :
743 265998 : ProcGlobal->xids[pgxactoff] = InvalidTransactionId;
744 265998 : proc->xid = InvalidTransactionId;
745 265998 : proc->vxid.lxid = InvalidLocalTransactionId;
746 265998 : proc->xmin = InvalidTransactionId;
747 :
748 : /* be sure this is cleared in abort */
749 265998 : proc->delayChkptFlags = 0;
750 :
751 265998 : proc->recoveryConflictPending = false;
752 :
753 : /* must be cleared with xid/xmin: */
754 : /* avoid unnecessarily dirtying shared cachelines */
755 265998 : if (proc->statusFlags & PROC_VACUUM_STATE_MASK)
756 : {
757 1276 : proc->statusFlags &= ~PROC_VACUUM_STATE_MASK;
758 1276 : ProcGlobal->statusFlags[proc->pgxactoff] = proc->statusFlags;
759 : }
760 :
761 : /* Clear the subtransaction-XID cache too while holding the lock */
762 : Assert(ProcGlobal->subxidStates[pgxactoff].count == proc->subxidStatus.count &&
763 : ProcGlobal->subxidStates[pgxactoff].overflowed == proc->subxidStatus.overflowed);
764 265998 : if (proc->subxidStatus.count > 0 || proc->subxidStatus.overflowed)
765 : {
766 1150 : ProcGlobal->subxidStates[pgxactoff].count = 0;
767 1150 : ProcGlobal->subxidStates[pgxactoff].overflowed = false;
768 1150 : proc->subxidStatus.count = 0;
769 1150 : proc->subxidStatus.overflowed = false;
770 : }
771 :
772 : /* Also advance global latestCompletedXid while holding the lock */
773 265998 : MaintainLatestCompletedXid(latestXid);
774 :
775 : /* Same with xactCompletionCount */
776 265998 : TransamVariables->xactCompletionCount++;
777 265998 : }
778 :
779 : /*
780 : * ProcArrayGroupClearXid -- group XID clearing
781 : *
782 : * When we cannot immediately acquire ProcArrayLock in exclusive mode at
783 : * commit time, add ourselves to a list of processes that need their XIDs
784 : * cleared. The first process to add itself to the list will acquire
785 : * ProcArrayLock in exclusive mode and perform ProcArrayEndTransactionInternal
786 : * on behalf of all group members. This avoids a great deal of contention
787 : * around ProcArrayLock when many processes are trying to commit at once,
788 : * since the lock need not be repeatedly handed off from one committing
789 : * process to the next.
790 : */
791 : static void
792 286 : ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
793 : {
794 286 : int pgprocno = GetNumberFromPGProc(proc);
795 286 : PROC_HDR *procglobal = ProcGlobal;
796 : uint32 nextidx;
797 : uint32 wakeidx;
798 :
799 : /* We should definitely have an XID to clear. */
800 : Assert(TransactionIdIsValid(proc->xid));
801 :
802 : /* Add ourselves to the list of processes needing a group XID clear. */
803 286 : proc->procArrayGroupMember = true;
804 286 : proc->procArrayGroupMemberXid = latestXid;
805 286 : nextidx = pg_atomic_read_u32(&procglobal->procArrayGroupFirst);
806 : while (true)
807 : {
808 286 : pg_atomic_write_u32(&proc->procArrayGroupNext, nextidx);
809 :
810 286 : if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,
811 : &nextidx,
812 : (uint32) pgprocno))
813 286 : break;
814 : }
815 :
816 : /*
817 : * If the list was not empty, the leader will clear our XID. It is
818 : * impossible to have followers without a leader because the first process
819 : * that has added itself to the list will always have nextidx as
820 : * INVALID_PROC_NUMBER.
821 : */
822 286 : if (nextidx != INVALID_PROC_NUMBER)
823 : {
824 22 : int extraWaits = 0;
825 :
826 : /* Sleep until the leader clears our XID. */
827 22 : pgstat_report_wait_start(WAIT_EVENT_PROCARRAY_GROUP_UPDATE);
828 : for (;;)
829 : {
830 : /* acts as a read barrier */
831 22 : PGSemaphoreLock(proc->sem);
832 22 : if (!proc->procArrayGroupMember)
833 22 : break;
834 0 : extraWaits++;
835 : }
836 22 : pgstat_report_wait_end();
837 :
838 : Assert(pg_atomic_read_u32(&proc->procArrayGroupNext) == INVALID_PROC_NUMBER);
839 :
840 : /* Fix semaphore count for any absorbed wakeups */
841 22 : while (extraWaits-- > 0)
842 0 : PGSemaphoreUnlock(proc->sem);
843 22 : return;
844 : }
845 :
846 : /* We are the leader. Acquire the lock on behalf of everyone. */
847 264 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
848 :
849 : /*
850 : * Now that we've got the lock, clear the list of processes waiting for
851 : * group XID clearing, saving a pointer to the head of the list. Trying
852 : * to pop elements one at a time could lead to an ABA problem.
853 : */
854 264 : nextidx = pg_atomic_exchange_u32(&procglobal->procArrayGroupFirst,
855 : INVALID_PROC_NUMBER);
856 :
857 : /* Remember head of list so we can perform wakeups after dropping lock. */
858 264 : wakeidx = nextidx;
859 :
860 : /* Walk the list and clear all XIDs. */
861 550 : while (nextidx != INVALID_PROC_NUMBER)
862 : {
863 286 : PGPROC *nextproc = &allProcs[nextidx];
864 :
865 286 : ProcArrayEndTransactionInternal(nextproc, nextproc->procArrayGroupMemberXid);
866 :
867 : /* Move to next proc in list. */
868 286 : nextidx = pg_atomic_read_u32(&nextproc->procArrayGroupNext);
869 : }
870 :
871 : /* We're done with the lock now. */
872 264 : LWLockRelease(ProcArrayLock);
873 :
874 : /*
875 : * Now that we've released the lock, go back and wake everybody up. We
876 : * don't do this under the lock so as to keep lock hold times to a
877 : * minimum. The system calls we need to perform to wake other processes
878 : * up are probably much slower than the simple memory writes we did while
879 : * holding the lock.
880 : */
881 550 : while (wakeidx != INVALID_PROC_NUMBER)
882 : {
883 286 : PGPROC *nextproc = &allProcs[wakeidx];
884 :
885 286 : wakeidx = pg_atomic_read_u32(&nextproc->procArrayGroupNext);
886 286 : pg_atomic_write_u32(&nextproc->procArrayGroupNext, INVALID_PROC_NUMBER);
887 :
888 : /* ensure all previous writes are visible before follower continues. */
889 286 : pg_write_barrier();
890 :
891 286 : nextproc->procArrayGroupMember = false;
892 :
893 286 : if (nextproc != MyProc)
894 22 : PGSemaphoreUnlock(nextproc->sem);
895 : }
896 : }
897 :
898 : /*
899 : * ProcArrayClearTransaction -- clear the transaction fields
900 : *
901 : * This is used after successfully preparing a 2-phase transaction. We are
902 : * not actually reporting the transaction's XID as no longer running --- it
903 : * will still appear as running because the 2PC's gxact is in the ProcArray
904 : * too. We just have to clear out our own PGPROC.
905 : */
906 : void
907 576 : ProcArrayClearTransaction(PGPROC *proc)
908 : {
909 : int pgxactoff;
910 :
911 : /*
912 : * Currently we need to lock ProcArrayLock exclusively here, as we
913 : * increment xactCompletionCount below. We also need it at least in shared
914 : * mode for pgproc->pgxactoff to stay the same below.
915 : *
916 : * We could however, as this action does not actually change anyone's view
917 : * of the set of running XIDs (our entry is duplicate with the gxact that
918 : * has already been inserted into the ProcArray), lower the lock level to
919 : * shared if we were to make xactCompletionCount an atomic variable. But
920 : * that doesn't seem worth it currently, as a 2PC commit is heavyweight
921 : * enough for this not to be the bottleneck. If it ever becomes a
922 : * bottleneck it may also be worth considering to combine this with the
923 : * subsequent ProcArrayRemove()
924 : */
925 576 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
926 :
927 576 : pgxactoff = proc->pgxactoff;
928 :
929 576 : ProcGlobal->xids[pgxactoff] = InvalidTransactionId;
930 576 : proc->xid = InvalidTransactionId;
931 :
932 576 : proc->vxid.lxid = InvalidLocalTransactionId;
933 576 : proc->xmin = InvalidTransactionId;
934 576 : proc->recoveryConflictPending = false;
935 :
936 : Assert(!(proc->statusFlags & PROC_VACUUM_STATE_MASK));
937 : Assert(!proc->delayChkptFlags);
938 :
939 : /*
940 : * Need to increment completion count even though transaction hasn't
941 : * really committed yet. The reason for that is that GetSnapshotData()
942 : * omits the xid of the current transaction, thus without the increment we
943 : * otherwise could end up reusing the snapshot later. Which would be bad,
944 : * because it might not count the prepared transaction as running.
945 : */
946 576 : TransamVariables->xactCompletionCount++;
947 :
948 : /* Clear the subtransaction-XID cache too */
949 : Assert(ProcGlobal->subxidStates[pgxactoff].count == proc->subxidStatus.count &&
950 : ProcGlobal->subxidStates[pgxactoff].overflowed == proc->subxidStatus.overflowed);
951 576 : if (proc->subxidStatus.count > 0 || proc->subxidStatus.overflowed)
952 : {
953 206 : ProcGlobal->subxidStates[pgxactoff].count = 0;
954 206 : ProcGlobal->subxidStates[pgxactoff].overflowed = false;
955 206 : proc->subxidStatus.count = 0;
956 206 : proc->subxidStatus.overflowed = false;
957 : }
958 :
959 576 : LWLockRelease(ProcArrayLock);
960 576 : }
961 :
962 : /*
963 : * Update TransamVariables->latestCompletedXid to point to latestXid if
964 : * currently older.
965 : */
966 : static void
967 267886 : MaintainLatestCompletedXid(TransactionId latestXid)
968 : {
969 267886 : FullTransactionId cur_latest = TransamVariables->latestCompletedXid;
970 :
971 : Assert(FullTransactionIdIsValid(cur_latest));
972 : Assert(!RecoveryInProgress());
973 : Assert(LWLockHeldByMe(ProcArrayLock));
974 :
975 267886 : if (TransactionIdPrecedes(XidFromFullTransactionId(cur_latest), latestXid))
976 : {
977 243232 : TransamVariables->latestCompletedXid =
978 243232 : FullXidRelativeTo(cur_latest, latestXid);
979 : }
980 :
981 : Assert(IsBootstrapProcessingMode() ||
982 : FullTransactionIdIsNormal(TransamVariables->latestCompletedXid));
983 267886 : }
984 :
985 : /*
986 : * Same as MaintainLatestCompletedXid, except for use during WAL replay.
987 : */
988 : static void
989 44272 : MaintainLatestCompletedXidRecovery(TransactionId latestXid)
990 : {
991 44272 : FullTransactionId cur_latest = TransamVariables->latestCompletedXid;
992 : FullTransactionId rel;
993 :
994 : Assert(AmStartupProcess() || !IsUnderPostmaster);
995 : Assert(LWLockHeldByMe(ProcArrayLock));
996 :
997 : /*
998 : * Need a FullTransactionId to compare latestXid with. Can't rely on
999 : * latestCompletedXid to be initialized in recovery. But in recovery it's
1000 : * safe to access nextXid without a lock for the startup process.
1001 : */
1002 44272 : rel = TransamVariables->nextXid;
1003 : Assert(FullTransactionIdIsValid(TransamVariables->nextXid));
1004 :
1005 88332 : if (!FullTransactionIdIsValid(cur_latest) ||
1006 44060 : TransactionIdPrecedes(XidFromFullTransactionId(cur_latest), latestXid))
1007 : {
1008 33942 : TransamVariables->latestCompletedXid =
1009 33942 : FullXidRelativeTo(rel, latestXid);
1010 : }
1011 :
1012 : Assert(FullTransactionIdIsNormal(TransamVariables->latestCompletedXid));
1013 44272 : }
1014 :
1015 : /*
1016 : * ProcArrayInitRecovery -- initialize recovery xid mgmt environment
1017 : *
1018 : * Remember up to where the startup process initialized the CLOG and subtrans
1019 : * so we can ensure it's initialized gaplessly up to the point where necessary
1020 : * while in recovery.
1021 : */
1022 : void
1023 212 : ProcArrayInitRecovery(TransactionId initializedUptoXID)
1024 : {
1025 : Assert(standbyState == STANDBY_INITIALIZED);
1026 : Assert(TransactionIdIsNormal(initializedUptoXID));
1027 :
1028 : /*
1029 : * we set latestObservedXid to the xid SUBTRANS has been initialized up
1030 : * to, so we can extend it from that point onwards in
1031 : * RecordKnownAssignedTransactionIds, and when we get consistent in
1032 : * ProcArrayApplyRecoveryInfo().
1033 : */
1034 212 : latestObservedXid = initializedUptoXID;
1035 212 : TransactionIdRetreat(latestObservedXid);
1036 212 : }
1037 :
1038 : /*
1039 : * ProcArrayApplyRecoveryInfo -- apply recovery info about xids
1040 : *
1041 : * Takes us through 3 states: Initialized, Pending and Ready.
1042 : * Normal case is to go all the way to Ready straight away, though there
1043 : * are atypical cases where we need to take it in steps.
1044 : *
1045 : * Use the data about running transactions on the primary to create the initial
1046 : * state of KnownAssignedXids. We also use these records to regularly prune
1047 : * KnownAssignedXids because we know it is possible that some transactions
1048 : * with FATAL errors fail to write abort records, which could cause eventual
1049 : * overflow.
1050 : *
1051 : * See comments for LogStandbySnapshot().
1052 : */
1053 : void
1054 1570 : ProcArrayApplyRecoveryInfo(RunningTransactions running)
1055 : {
1056 : TransactionId *xids;
1057 : TransactionId advanceNextXid;
1058 : int nxids;
1059 : int i;
1060 :
1061 : Assert(standbyState >= STANDBY_INITIALIZED);
1062 : Assert(TransactionIdIsValid(running->nextXid));
1063 : Assert(TransactionIdIsValid(running->oldestRunningXid));
1064 : Assert(TransactionIdIsNormal(running->latestCompletedXid));
1065 :
1066 : /*
1067 : * Remove stale transactions, if any.
1068 : */
1069 1570 : ExpireOldKnownAssignedTransactionIds(running->oldestRunningXid);
1070 :
1071 : /*
1072 : * Adjust TransamVariables->nextXid before StandbyReleaseOldLocks(),
1073 : * because we will need it up to date for accessing two-phase transactions
1074 : * in StandbyReleaseOldLocks().
1075 : */
1076 1570 : advanceNextXid = running->nextXid;
1077 1570 : TransactionIdRetreat(advanceNextXid);
1078 1570 : AdvanceNextFullTransactionIdPastXid(advanceNextXid);
1079 : Assert(FullTransactionIdIsValid(TransamVariables->nextXid));
1080 :
1081 : /*
1082 : * Remove stale locks, if any.
1083 : */
1084 1570 : StandbyReleaseOldLocks(running->oldestRunningXid);
1085 :
1086 : /*
1087 : * If our snapshot is already valid, nothing else to do...
1088 : */
1089 1570 : if (standbyState == STANDBY_SNAPSHOT_READY)
1090 1358 : return;
1091 :
1092 : /*
1093 : * If our initial RunningTransactionsData had an overflowed snapshot then
1094 : * we knew we were missing some subxids from our snapshot. If we continue
1095 : * to see overflowed snapshots then we might never be able to start up, so
1096 : * we make another test to see if our snapshot is now valid. We know that
1097 : * the missing subxids are equal to or earlier than nextXid. After we
1098 : * initialise we continue to apply changes during recovery, so once the
1099 : * oldestRunningXid is later than the nextXid from the initial snapshot we
1100 : * know that we no longer have missing information and can mark the
1101 : * snapshot as valid.
1102 : */
1103 212 : if (standbyState == STANDBY_SNAPSHOT_PENDING)
1104 : {
1105 : /*
1106 : * If the snapshot isn't overflowed or if its empty we can reset our
1107 : * pending state and use this snapshot instead.
1108 : */
1109 0 : if (running->subxid_status != SUBXIDS_MISSING || running->xcnt == 0)
1110 : {
1111 : /*
1112 : * If we have already collected known assigned xids, we need to
1113 : * throw them away before we apply the recovery snapshot.
1114 : */
1115 0 : KnownAssignedXidsReset();
1116 0 : standbyState = STANDBY_INITIALIZED;
1117 : }
1118 : else
1119 : {
1120 0 : if (TransactionIdPrecedes(standbySnapshotPendingXmin,
1121 : running->oldestRunningXid))
1122 : {
1123 0 : standbyState = STANDBY_SNAPSHOT_READY;
1124 0 : elog(DEBUG1,
1125 : "recovery snapshots are now enabled");
1126 : }
1127 : else
1128 0 : elog(DEBUG1,
1129 : "recovery snapshot waiting for non-overflowed snapshot or "
1130 : "until oldest active xid on standby is at least %u (now %u)",
1131 : standbySnapshotPendingXmin,
1132 : running->oldestRunningXid);
1133 0 : return;
1134 : }
1135 : }
1136 :
1137 : Assert(standbyState == STANDBY_INITIALIZED);
1138 :
1139 : /*
1140 : * NB: this can be reached at least twice, so make sure new code can deal
1141 : * with that.
1142 : */
1143 :
1144 : /*
1145 : * Nobody else is running yet, but take locks anyhow
1146 : */
1147 212 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
1148 :
1149 : /*
1150 : * KnownAssignedXids is sorted so we cannot just add the xids, we have to
1151 : * sort them first.
1152 : *
1153 : * Some of the new xids are top-level xids and some are subtransactions.
1154 : * We don't call SubTransSetParent because it doesn't matter yet. If we
1155 : * aren't overflowed then all xids will fit in snapshot and so we don't
1156 : * need subtrans. If we later overflow, an xid assignment record will add
1157 : * xids to subtrans. If RunningTransactionsData is overflowed then we
1158 : * don't have enough information to correctly update subtrans anyway.
1159 : */
1160 :
1161 : /*
1162 : * Allocate a temporary array to avoid modifying the array passed as
1163 : * argument.
1164 : */
1165 212 : xids = palloc(sizeof(TransactionId) * (running->xcnt + running->subxcnt));
1166 :
1167 : /*
1168 : * Add to the temp array any xids which have not already completed.
1169 : */
1170 212 : nxids = 0;
1171 220 : for (i = 0; i < running->xcnt + running->subxcnt; i++)
1172 : {
1173 8 : TransactionId xid = running->xids[i];
1174 :
1175 : /*
1176 : * The running-xacts snapshot can contain xids that were still visible
1177 : * in the procarray when the snapshot was taken, but were already
1178 : * WAL-logged as completed. They're not running anymore, so ignore
1179 : * them.
1180 : */
1181 8 : if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid))
1182 0 : continue;
1183 :
1184 8 : xids[nxids++] = xid;
1185 : }
1186 :
1187 212 : if (nxids > 0)
1188 : {
1189 8 : if (procArray->numKnownAssignedXids != 0)
1190 : {
1191 0 : LWLockRelease(ProcArrayLock);
1192 0 : elog(ERROR, "KnownAssignedXids is not empty");
1193 : }
1194 :
1195 : /*
1196 : * Sort the array so that we can add them safely into
1197 : * KnownAssignedXids.
1198 : *
1199 : * We have to sort them logically, because in KnownAssignedXidsAdd we
1200 : * call TransactionIdFollowsOrEquals and so on. But we know these XIDs
1201 : * come from RUNNING_XACTS, which means there are only normal XIDs
1202 : * from the same epoch, so this is safe.
1203 : */
1204 8 : qsort(xids, nxids, sizeof(TransactionId), xidLogicalComparator);
1205 :
1206 : /*
1207 : * Add the sorted snapshot into KnownAssignedXids. The running-xacts
1208 : * snapshot may include duplicated xids because of prepared
1209 : * transactions, so ignore them.
1210 : */
1211 16 : for (i = 0; i < nxids; i++)
1212 : {
1213 8 : if (i > 0 && TransactionIdEquals(xids[i - 1], xids[i]))
1214 : {
1215 0 : elog(DEBUG1,
1216 : "found duplicated transaction %u for KnownAssignedXids insertion",
1217 : xids[i]);
1218 0 : continue;
1219 : }
1220 8 : KnownAssignedXidsAdd(xids[i], xids[i], true);
1221 : }
1222 :
1223 8 : KnownAssignedXidsDisplay(DEBUG3);
1224 : }
1225 :
1226 212 : pfree(xids);
1227 :
1228 : /*
1229 : * latestObservedXid is at least set to the point where SUBTRANS was
1230 : * started up to (cf. ProcArrayInitRecovery()) or to the biggest xid
1231 : * RecordKnownAssignedTransactionIds() was called for. Initialize
1232 : * subtrans from thereon, up to nextXid - 1.
1233 : *
1234 : * We need to duplicate parts of RecordKnownAssignedTransactionId() here,
1235 : * because we've just added xids to the known assigned xids machinery that
1236 : * haven't gone through RecordKnownAssignedTransactionId().
1237 : */
1238 : Assert(TransactionIdIsNormal(latestObservedXid));
1239 212 : TransactionIdAdvance(latestObservedXid);
1240 424 : while (TransactionIdPrecedes(latestObservedXid, running->nextXid))
1241 : {
1242 0 : ExtendSUBTRANS(latestObservedXid);
1243 0 : TransactionIdAdvance(latestObservedXid);
1244 : }
1245 212 : TransactionIdRetreat(latestObservedXid); /* = running->nextXid - 1 */
1246 :
1247 : /* ----------
1248 : * Now we've got the running xids we need to set the global values that
1249 : * are used to track snapshots as they evolve further.
1250 : *
1251 : * - latestCompletedXid which will be the xmax for snapshots
1252 : * - lastOverflowedXid which shows whether snapshots overflow
1253 : * - nextXid
1254 : *
1255 : * If the snapshot overflowed, then we still initialise with what we know,
1256 : * but the recovery snapshot isn't fully valid yet because we know there
1257 : * are some subxids missing. We don't know the specific subxids that are
1258 : * missing, so conservatively assume the last one is latestObservedXid.
1259 : * ----------
1260 : */
1261 212 : if (running->subxid_status == SUBXIDS_MISSING)
1262 : {
1263 0 : standbyState = STANDBY_SNAPSHOT_PENDING;
1264 :
1265 0 : standbySnapshotPendingXmin = latestObservedXid;
1266 0 : procArray->lastOverflowedXid = latestObservedXid;
1267 : }
1268 : else
1269 : {
1270 212 : standbyState = STANDBY_SNAPSHOT_READY;
1271 :
1272 212 : standbySnapshotPendingXmin = InvalidTransactionId;
1273 :
1274 : /*
1275 : * If the 'xids' array didn't include all subtransactions, we have to
1276 : * mark any snapshots taken as overflowed.
1277 : */
1278 212 : if (running->subxid_status == SUBXIDS_IN_SUBTRANS)
1279 52 : procArray->lastOverflowedXid = latestObservedXid;
1280 : else
1281 : {
1282 : Assert(running->subxid_status == SUBXIDS_IN_ARRAY);
1283 160 : procArray->lastOverflowedXid = InvalidTransactionId;
1284 : }
1285 : }
1286 :
1287 : /*
1288 : * If a transaction wrote a commit record in the gap between taking and
1289 : * logging the snapshot then latestCompletedXid may already be higher than
1290 : * the value from the snapshot, so check before we use the incoming value.
1291 : * It also might not yet be set at all.
1292 : */
1293 212 : MaintainLatestCompletedXidRecovery(running->latestCompletedXid);
1294 :
1295 : /*
1296 : * NB: No need to increment TransamVariables->xactCompletionCount here,
1297 : * nobody can see it yet.
1298 : */
1299 :
1300 212 : LWLockRelease(ProcArrayLock);
1301 :
1302 212 : KnownAssignedXidsDisplay(DEBUG3);
1303 212 : if (standbyState == STANDBY_SNAPSHOT_READY)
1304 212 : elog(DEBUG1, "recovery snapshots are now enabled");
1305 : else
1306 0 : elog(DEBUG1,
1307 : "recovery snapshot waiting for non-overflowed snapshot or "
1308 : "until oldest active xid on standby is at least %u (now %u)",
1309 : standbySnapshotPendingXmin,
1310 : running->oldestRunningXid);
1311 : }
1312 :
1313 : /*
1314 : * ProcArrayApplyXidAssignment
1315 : * Process an XLOG_XACT_ASSIGNMENT WAL record
1316 : */
1317 : void
1318 42 : ProcArrayApplyXidAssignment(TransactionId topxid,
1319 : int nsubxids, TransactionId *subxids)
1320 : {
1321 : TransactionId max_xid;
1322 : int i;
1323 :
1324 : Assert(standbyState >= STANDBY_INITIALIZED);
1325 :
1326 42 : max_xid = TransactionIdLatest(topxid, nsubxids, subxids);
1327 :
1328 : /*
1329 : * Mark all the subtransactions as observed.
1330 : *
1331 : * NOTE: This will fail if the subxid contains too many previously
1332 : * unobserved xids to fit into known-assigned-xids. That shouldn't happen
1333 : * as the code stands, because xid-assignment records should never contain
1334 : * more than PGPROC_MAX_CACHED_SUBXIDS entries.
1335 : */
1336 42 : RecordKnownAssignedTransactionIds(max_xid);
1337 :
1338 : /*
1339 : * Notice that we update pg_subtrans with the top-level xid, rather than
1340 : * the parent xid. This is a difference between normal processing and
1341 : * recovery, yet is still correct in all cases. The reason is that
1342 : * subtransaction commit is not marked in clog until commit processing, so
1343 : * all aborted subtransactions have already been clearly marked in clog.
1344 : * As a result we are able to refer directly to the top-level
1345 : * transaction's state rather than skipping through all the intermediate
1346 : * states in the subtransaction tree. This should be the first time we
1347 : * have attempted to SubTransSetParent().
1348 : */
1349 2730 : for (i = 0; i < nsubxids; i++)
1350 2688 : SubTransSetParent(subxids[i], topxid);
1351 :
1352 : /* KnownAssignedXids isn't maintained yet, so we're done for now */
1353 42 : if (standbyState == STANDBY_INITIALIZED)
1354 0 : return;
1355 :
1356 : /*
1357 : * Uses same locking as transaction commit
1358 : */
1359 42 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
1360 :
1361 : /*
1362 : * Remove subxids from known-assigned-xacts.
1363 : */
1364 42 : KnownAssignedXidsRemoveTree(InvalidTransactionId, nsubxids, subxids);
1365 :
1366 : /*
1367 : * Advance lastOverflowedXid to be at least the last of these subxids.
1368 : */
1369 42 : if (TransactionIdPrecedes(procArray->lastOverflowedXid, max_xid))
1370 42 : procArray->lastOverflowedXid = max_xid;
1371 :
1372 42 : LWLockRelease(ProcArrayLock);
1373 : }
1374 :
1375 : /*
1376 : * TransactionIdIsInProgress -- is given transaction running in some backend
1377 : *
1378 : * Aside from some shortcuts such as checking RecentXmin and our own Xid,
1379 : * there are four possibilities for finding a running transaction:
1380 : *
1381 : * 1. The given Xid is a main transaction Id. We will find this out cheaply
1382 : * by looking at ProcGlobal->xids.
1383 : *
1384 : * 2. The given Xid is one of the cached subxact Xids in the PGPROC array.
1385 : * We can find this out cheaply too.
1386 : *
1387 : * 3. In Hot Standby mode, we must search the KnownAssignedXids list to see
1388 : * if the Xid is running on the primary.
1389 : *
1390 : * 4. Search the SubTrans tree to find the Xid's topmost parent, and then see
1391 : * if that is running according to ProcGlobal->xids[] or KnownAssignedXids.
1392 : * This is the slowest way, but sadly it has to be done always if the others
1393 : * failed, unless we see that the cached subxact sets are complete (none have
1394 : * overflowed).
1395 : *
1396 : * ProcArrayLock has to be held while we do 1, 2, 3. If we save the top Xids
1397 : * while doing 1 and 3, we can release the ProcArrayLock while we do 4.
1398 : * This buys back some concurrency (and we can't retrieve the main Xids from
1399 : * ProcGlobal->xids[] again anyway; see GetNewTransactionId).
1400 : */
1401 : bool
1402 21083092 : TransactionIdIsInProgress(TransactionId xid)
1403 : {
1404 : static TransactionId *xids = NULL;
1405 : static TransactionId *other_xids;
1406 : XidCacheStatus *other_subxidstates;
1407 21083092 : int nxids = 0;
1408 21083092 : ProcArrayStruct *arrayP = procArray;
1409 : TransactionId topxid;
1410 : TransactionId latestCompletedXid;
1411 : int mypgxactoff;
1412 : int numProcs;
1413 : int j;
1414 :
1415 : /*
1416 : * Don't bother checking a transaction older than RecentXmin; it could not
1417 : * possibly still be running. (Note: in particular, this guarantees that
1418 : * we reject InvalidTransactionId, FrozenTransactionId, etc as not
1419 : * running.)
1420 : */
1421 21083092 : if (TransactionIdPrecedes(xid, RecentXmin))
1422 : {
1423 : xc_by_recent_xmin_inc();
1424 9259172 : return false;
1425 : }
1426 :
1427 : /*
1428 : * We may have just checked the status of this transaction, so if it is
1429 : * already known to be completed, we can fall out without any access to
1430 : * shared memory.
1431 : */
1432 11823920 : if (TransactionIdEquals(cachedXidIsNotInProgress, xid))
1433 : {
1434 : xc_by_known_xact_inc();
1435 2088812 : return false;
1436 : }
1437 :
1438 : /*
1439 : * Also, we can handle our own transaction (and subtransactions) without
1440 : * any access to shared memory.
1441 : */
1442 9735108 : if (TransactionIdIsCurrentTransactionId(xid))
1443 : {
1444 : xc_by_my_xact_inc();
1445 395974 : return true;
1446 : }
1447 :
1448 : /*
1449 : * If first time through, get workspace to remember main XIDs in. We
1450 : * malloc it permanently to avoid repeated palloc/pfree overhead.
1451 : */
1452 9339134 : if (xids == NULL)
1453 : {
1454 : /*
1455 : * In hot standby mode, reserve enough space to hold all xids in the
1456 : * known-assigned list. If we later finish recovery, we no longer need
1457 : * the bigger array, but we don't bother to shrink it.
1458 : */
1459 3066 : int maxxids = RecoveryInProgress() ? TOTAL_MAX_CACHED_SUBXIDS : arrayP->maxProcs;
1460 :
1461 3066 : xids = (TransactionId *) malloc(maxxids * sizeof(TransactionId));
1462 3066 : if (xids == NULL)
1463 0 : ereport(ERROR,
1464 : (errcode(ERRCODE_OUT_OF_MEMORY),
1465 : errmsg("out of memory")));
1466 : }
1467 :
1468 9339134 : other_xids = ProcGlobal->xids;
1469 9339134 : other_subxidstates = ProcGlobal->subxidStates;
1470 :
1471 9339134 : LWLockAcquire(ProcArrayLock, LW_SHARED);
1472 :
1473 : /*
1474 : * Now that we have the lock, we can check latestCompletedXid; if the
1475 : * target Xid is after that, it's surely still running.
1476 : */
1477 9339134 : latestCompletedXid =
1478 9339134 : XidFromFullTransactionId(TransamVariables->latestCompletedXid);
1479 9339134 : if (TransactionIdPrecedes(latestCompletedXid, xid))
1480 : {
1481 71192 : LWLockRelease(ProcArrayLock);
1482 : xc_by_latest_xid_inc();
1483 71192 : return true;
1484 : }
1485 :
1486 : /* No shortcuts, gotta grovel through the array */
1487 9267942 : mypgxactoff = MyProc->pgxactoff;
1488 9267942 : numProcs = arrayP->numProcs;
1489 9527126 : for (int pgxactoff = 0; pgxactoff < numProcs; pgxactoff++)
1490 : {
1491 : int pgprocno;
1492 : PGPROC *proc;
1493 : TransactionId pxid;
1494 : int pxids;
1495 :
1496 : /* Ignore ourselves --- dealt with it above */
1497 9504344 : if (pgxactoff == mypgxactoff)
1498 25378 : continue;
1499 :
1500 : /* Fetch xid just once - see GetNewTransactionId */
1501 9478966 : pxid = UINT32_ACCESS_ONCE(other_xids[pgxactoff]);
1502 :
1503 9478966 : if (!TransactionIdIsValid(pxid))
1504 158194 : continue;
1505 :
1506 : /*
1507 : * Step 1: check the main Xid
1508 : */
1509 9320772 : if (TransactionIdEquals(pxid, xid))
1510 : {
1511 9244632 : LWLockRelease(ProcArrayLock);
1512 : xc_by_main_xid_inc();
1513 9244632 : return true;
1514 : }
1515 :
1516 : /*
1517 : * We can ignore main Xids that are younger than the target Xid, since
1518 : * the target could not possibly be their child.
1519 : */
1520 76140 : if (TransactionIdPrecedes(xid, pxid))
1521 36928 : continue;
1522 :
1523 : /*
1524 : * Step 2: check the cached child-Xids arrays
1525 : */
1526 39212 : pxids = other_subxidstates[pgxactoff].count;
1527 39212 : pg_read_barrier(); /* pairs with barrier in GetNewTransactionId() */
1528 39212 : pgprocno = arrayP->pgprocnos[pgxactoff];
1529 39212 : proc = &allProcs[pgprocno];
1530 105916 : for (j = pxids - 1; j >= 0; j--)
1531 : {
1532 : /* Fetch xid just once - see GetNewTransactionId */
1533 67232 : TransactionId cxid = UINT32_ACCESS_ONCE(proc->subxids.xids[j]);
1534 :
1535 67232 : if (TransactionIdEquals(cxid, xid))
1536 : {
1537 528 : LWLockRelease(ProcArrayLock);
1538 : xc_by_child_xid_inc();
1539 528 : return true;
1540 : }
1541 : }
1542 :
1543 : /*
1544 : * Save the main Xid for step 4. We only need to remember main Xids
1545 : * that have uncached children. (Note: there is no race condition
1546 : * here because the overflowed flag cannot be cleared, only set, while
1547 : * we hold ProcArrayLock. So we can't miss an Xid that we need to
1548 : * worry about.)
1549 : */
1550 38684 : if (other_subxidstates[pgxactoff].overflowed)
1551 426 : xids[nxids++] = pxid;
1552 : }
1553 :
1554 : /*
1555 : * Step 3: in hot standby mode, check the known-assigned-xids list. XIDs
1556 : * in the list must be treated as running.
1557 : */
1558 22782 : if (RecoveryInProgress())
1559 : {
1560 : /* none of the PGPROC entries should have XIDs in hot standby mode */
1561 : Assert(nxids == 0);
1562 :
1563 2 : if (KnownAssignedXidExists(xid))
1564 : {
1565 0 : LWLockRelease(ProcArrayLock);
1566 : xc_by_known_assigned_inc();
1567 0 : return true;
1568 : }
1569 :
1570 : /*
1571 : * If the KnownAssignedXids overflowed, we have to check pg_subtrans
1572 : * too. Fetch all xids from KnownAssignedXids that are lower than
1573 : * xid, since if xid is a subtransaction its parent will always have a
1574 : * lower value. Note we will collect both main and subXIDs here, but
1575 : * there's no help for it.
1576 : */
1577 2 : if (TransactionIdPrecedesOrEquals(xid, procArray->lastOverflowedXid))
1578 0 : nxids = KnownAssignedXidsGet(xids, xid);
1579 : }
1580 :
1581 22782 : LWLockRelease(ProcArrayLock);
1582 :
1583 : /*
1584 : * If none of the relevant caches overflowed, we know the Xid is not
1585 : * running without even looking at pg_subtrans.
1586 : */
1587 22782 : if (nxids == 0)
1588 : {
1589 : xc_no_overflow_inc();
1590 22356 : cachedXidIsNotInProgress = xid;
1591 22356 : return false;
1592 : }
1593 :
1594 : /*
1595 : * Step 4: have to check pg_subtrans.
1596 : *
1597 : * At this point, we know it's either a subtransaction of one of the Xids
1598 : * in xids[], or it's not running. If it's an already-failed
1599 : * subtransaction, we want to say "not running" even though its parent may
1600 : * still be running. So first, check pg_xact to see if it's been aborted.
1601 : */
1602 : xc_slow_answer_inc();
1603 :
1604 426 : if (TransactionIdDidAbort(xid))
1605 : {
1606 0 : cachedXidIsNotInProgress = xid;
1607 0 : return false;
1608 : }
1609 :
1610 : /*
1611 : * It isn't aborted, so check whether the transaction tree it belongs to
1612 : * is still running (or, more precisely, whether it was running when we
1613 : * held ProcArrayLock).
1614 : */
1615 426 : topxid = SubTransGetTopmostTransaction(xid);
1616 : Assert(TransactionIdIsValid(topxid));
1617 740 : if (!TransactionIdEquals(topxid, xid) &&
1618 314 : pg_lfind32(topxid, xids, nxids))
1619 314 : return true;
1620 :
1621 112 : cachedXidIsNotInProgress = xid;
1622 112 : return false;
1623 : }
1624 :
1625 :
1626 : /*
1627 : * Determine XID horizons.
1628 : *
1629 : * This is used by wrapper functions like GetOldestNonRemovableTransactionId()
1630 : * (for VACUUM), GetReplicationHorizons() (for hot_standby_feedback), etc as
1631 : * well as "internally" by GlobalVisUpdate() (see comment above struct
1632 : * GlobalVisState).
1633 : *
1634 : * See the definition of ComputeXidHorizonsResult for the various computed
1635 : * horizons.
1636 : *
1637 : * For VACUUM separate horizons (used to decide which deleted tuples must
1638 : * be preserved), for shared and non-shared tables are computed. For shared
1639 : * relations backends in all databases must be considered, but for non-shared
1640 : * relations that's not required, since only backends in my own database could
1641 : * ever see the tuples in them. Also, we can ignore concurrently running lazy
1642 : * VACUUMs because (a) they must be working on other tables, and (b) they
1643 : * don't need to do snapshot-based lookups.
1644 : *
1645 : * This also computes a horizon used to truncate pg_subtrans. For that
1646 : * backends in all databases have to be considered, and concurrently running
1647 : * lazy VACUUMs cannot be ignored, as they still may perform pg_subtrans
1648 : * accesses.
1649 : *
1650 : * Note: we include all currently running xids in the set of considered xids.
1651 : * This ensures that if a just-started xact has not yet set its snapshot,
1652 : * when it does set the snapshot it cannot set xmin less than what we compute.
1653 : * See notes in src/backend/access/transam/README.
1654 : *
1655 : * Note: despite the above, it's possible for the calculated values to move
1656 : * backwards on repeated calls. The calculated values are conservative, so
1657 : * that anything older is definitely not considered as running by anyone
1658 : * anymore, but the exact values calculated depend on a number of things. For
1659 : * example, if there are no transactions running in the current database, the
1660 : * horizon for normal tables will be latestCompletedXid. If a transaction
1661 : * begins after that, its xmin will include in-progress transactions in other
1662 : * databases that started earlier, so another call will return a lower value.
1663 : * Nonetheless it is safe to vacuum a table in the current database with the
1664 : * first result. There are also replication-related effects: a walsender
1665 : * process can set its xmin based on transactions that are no longer running
1666 : * on the primary but are still being replayed on the standby, thus possibly
1667 : * making the values go backwards. In this case there is a possibility that
1668 : * we lose data that the standby would like to have, but unless the standby
1669 : * uses a replication slot to make its xmin persistent there is little we can
1670 : * do about that --- data is only protected if the walsender runs continuously
1671 : * while queries are executed on the standby. (The Hot Standby code deals
1672 : * with such cases by failing standby queries that needed to access
1673 : * already-removed data, so there's no integrity bug.)
1674 : *
1675 : * Note: the approximate horizons (see definition of GlobalVisState) are
1676 : * updated by the computations done here. That's currently required for
1677 : * correctness and a small optimization. Without doing so it's possible that
1678 : * heap vacuum's call to heap_page_prune_and_freeze() uses a more conservative
1679 : * horizon than later when deciding which tuples can be removed - which the
1680 : * code doesn't expect (breaking HOT).
1681 : */
1682 : static void
1683 420090 : ComputeXidHorizons(ComputeXidHorizonsResult *h)
1684 : {
1685 420090 : ProcArrayStruct *arrayP = procArray;
1686 : TransactionId kaxmin;
1687 420090 : bool in_recovery = RecoveryInProgress();
1688 420090 : TransactionId *other_xids = ProcGlobal->xids;
1689 :
1690 : /* inferred after ProcArrayLock is released */
1691 420090 : h->catalog_oldest_nonremovable = InvalidTransactionId;
1692 :
1693 420090 : LWLockAcquire(ProcArrayLock, LW_SHARED);
1694 :
1695 420090 : h->latest_completed = TransamVariables->latestCompletedXid;
1696 :
1697 : /*
1698 : * We initialize the MIN() calculation with latestCompletedXid + 1. This
1699 : * is a lower bound for the XIDs that might appear in the ProcArray later,
1700 : * and so protects us against overestimating the result due to future
1701 : * additions.
1702 : */
1703 : {
1704 : TransactionId initial;
1705 :
1706 420090 : initial = XidFromFullTransactionId(h->latest_completed);
1707 : Assert(TransactionIdIsValid(initial));
1708 420090 : TransactionIdAdvance(initial);
1709 :
1710 420090 : h->oldest_considered_running = initial;
1711 420090 : h->shared_oldest_nonremovable = initial;
1712 420090 : h->data_oldest_nonremovable = initial;
1713 :
1714 : /*
1715 : * Only modifications made by this backend affect the horizon for
1716 : * temporary relations. Instead of a check in each iteration of the
1717 : * loop over all PGPROCs it is cheaper to just initialize to the
1718 : * current top-level xid any.
1719 : *
1720 : * Without an assigned xid we could use a horizon as aggressive as
1721 : * GetNewTransactionId(), but we can get away with the much cheaper
1722 : * latestCompletedXid + 1: If this backend has no xid there, by
1723 : * definition, can't be any newer changes in the temp table than
1724 : * latestCompletedXid.
1725 : */
1726 420090 : if (TransactionIdIsValid(MyProc->xid))
1727 66824 : h->temp_oldest_nonremovable = MyProc->xid;
1728 : else
1729 353266 : h->temp_oldest_nonremovable = initial;
1730 : }
1731 :
1732 : /*
1733 : * Fetch slot horizons while ProcArrayLock is held - the
1734 : * LWLockAcquire/LWLockRelease are a barrier, ensuring this happens inside
1735 : * the lock.
1736 : */
1737 420090 : h->slot_xmin = procArray->replication_slot_xmin;
1738 420090 : h->slot_catalog_xmin = procArray->replication_slot_catalog_xmin;
1739 :
1740 2646408 : for (int index = 0; index < arrayP->numProcs; index++)
1741 : {
1742 2226318 : int pgprocno = arrayP->pgprocnos[index];
1743 2226318 : PGPROC *proc = &allProcs[pgprocno];
1744 2226318 : int8 statusFlags = ProcGlobal->statusFlags[index];
1745 : TransactionId xid;
1746 : TransactionId xmin;
1747 :
1748 : /* Fetch xid just once - see GetNewTransactionId */
1749 2226318 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
1750 2226318 : xmin = UINT32_ACCESS_ONCE(proc->xmin);
1751 :
1752 : /*
1753 : * Consider both the transaction's Xmin, and its Xid.
1754 : *
1755 : * We must check both because a transaction might have an Xmin but not
1756 : * (yet) an Xid; conversely, if it has an Xid, that could determine
1757 : * some not-yet-set Xmin.
1758 : */
1759 2226318 : xmin = TransactionIdOlder(xmin, xid);
1760 :
1761 : /* if neither is set, this proc doesn't influence the horizon */
1762 2226318 : if (!TransactionIdIsValid(xmin))
1763 924558 : continue;
1764 :
1765 : /*
1766 : * Don't ignore any procs when determining which transactions might be
1767 : * considered running. While slots should ensure logical decoding
1768 : * backends are protected even without this check, it can't hurt to
1769 : * include them here as well..
1770 : */
1771 1301760 : h->oldest_considered_running =
1772 1301760 : TransactionIdOlder(h->oldest_considered_running, xmin);
1773 :
1774 : /*
1775 : * Skip over backends either vacuuming (which is ok with rows being
1776 : * removed, as long as pg_subtrans is not truncated) or doing logical
1777 : * decoding (which manages xmin separately, check below).
1778 : */
1779 1301760 : if (statusFlags & (PROC_IN_VACUUM | PROC_IN_LOGICAL_DECODING))
1780 491674 : continue;
1781 :
1782 : /* shared tables need to take backends in all databases into account */
1783 810086 : h->shared_oldest_nonremovable =
1784 810086 : TransactionIdOlder(h->shared_oldest_nonremovable, xmin);
1785 :
1786 : /*
1787 : * Normally sessions in other databases are ignored for anything but
1788 : * the shared horizon.
1789 : *
1790 : * However, include them when MyDatabaseId is not (yet) set. A
1791 : * backend in the process of starting up must not compute a "too
1792 : * aggressive" horizon, otherwise we could end up using it to prune
1793 : * still-needed data away. If the current backend never connects to a
1794 : * database this is harmless, because data_oldest_nonremovable will
1795 : * never be utilized.
1796 : *
1797 : * Also, sessions marked with PROC_AFFECTS_ALL_HORIZONS should always
1798 : * be included. (This flag is used for hot standby feedback, which
1799 : * can't be tied to a specific database.)
1800 : *
1801 : * Also, while in recovery we cannot compute an accurate per-database
1802 : * horizon, as all xids are managed via the KnownAssignedXids
1803 : * machinery.
1804 : */
1805 810086 : if (proc->databaseId == MyDatabaseId ||
1806 34012 : MyDatabaseId == InvalidOid ||
1807 21400 : (statusFlags & PROC_AFFECTS_ALL_HORIZONS) ||
1808 : in_recovery)
1809 : {
1810 788690 : h->data_oldest_nonremovable =
1811 788690 : TransactionIdOlder(h->data_oldest_nonremovable, xmin);
1812 : }
1813 : }
1814 :
1815 : /*
1816 : * If in recovery fetch oldest xid in KnownAssignedXids, will be applied
1817 : * after lock is released.
1818 : */
1819 420090 : if (in_recovery)
1820 700 : kaxmin = KnownAssignedXidsGetOldestXmin();
1821 :
1822 : /*
1823 : * No other information from shared state is needed, release the lock
1824 : * immediately. The rest of the computations can be done without a lock.
1825 : */
1826 420090 : LWLockRelease(ProcArrayLock);
1827 :
1828 420090 : if (in_recovery)
1829 : {
1830 700 : h->oldest_considered_running =
1831 700 : TransactionIdOlder(h->oldest_considered_running, kaxmin);
1832 700 : h->shared_oldest_nonremovable =
1833 700 : TransactionIdOlder(h->shared_oldest_nonremovable, kaxmin);
1834 700 : h->data_oldest_nonremovable =
1835 700 : TransactionIdOlder(h->data_oldest_nonremovable, kaxmin);
1836 : /* temp relations cannot be accessed in recovery */
1837 : }
1838 :
1839 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1840 : h->shared_oldest_nonremovable));
1841 : Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
1842 : h->data_oldest_nonremovable));
1843 :
1844 : /*
1845 : * Check whether there are replication slots requiring an older xmin.
1846 : */
1847 420090 : h->shared_oldest_nonremovable =
1848 420090 : TransactionIdOlder(h->shared_oldest_nonremovable, h->slot_xmin);
1849 420090 : h->data_oldest_nonremovable =
1850 420090 : TransactionIdOlder(h->data_oldest_nonremovable, h->slot_xmin);
1851 :
1852 : /*
1853 : * The only difference between catalog / data horizons is that the slot's
1854 : * catalog xmin is applied to the catalog one (so catalogs can be accessed
1855 : * for logical decoding). Initialize with data horizon, and then back up
1856 : * further if necessary. Have to back up the shared horizon as well, since
1857 : * that also can contain catalogs.
1858 : */
1859 420090 : h->shared_oldest_nonremovable_raw = h->shared_oldest_nonremovable;
1860 420090 : h->shared_oldest_nonremovable =
1861 420090 : TransactionIdOlder(h->shared_oldest_nonremovable,
1862 : h->slot_catalog_xmin);
1863 420090 : h->catalog_oldest_nonremovable = h->data_oldest_nonremovable;
1864 420090 : h->catalog_oldest_nonremovable =
1865 420090 : TransactionIdOlder(h->catalog_oldest_nonremovable,
1866 : h->slot_catalog_xmin);
1867 :
1868 : /*
1869 : * It's possible that slots backed up the horizons further than
1870 : * oldest_considered_running. Fix.
1871 : */
1872 420090 : h->oldest_considered_running =
1873 420090 : TransactionIdOlder(h->oldest_considered_running,
1874 : h->shared_oldest_nonremovable);
1875 420090 : h->oldest_considered_running =
1876 420090 : TransactionIdOlder(h->oldest_considered_running,
1877 : h->catalog_oldest_nonremovable);
1878 420090 : h->oldest_considered_running =
1879 420090 : TransactionIdOlder(h->oldest_considered_running,
1880 : h->data_oldest_nonremovable);
1881 :
1882 : /*
1883 : * shared horizons have to be at least as old as the oldest visible in
1884 : * current db
1885 : */
1886 : Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
1887 : h->data_oldest_nonremovable));
1888 : Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
1889 : h->catalog_oldest_nonremovable));
1890 :
1891 : /*
1892 : * Horizons need to ensure that pg_subtrans access is still possible for
1893 : * the relevant backends.
1894 : */
1895 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1896 : h->shared_oldest_nonremovable));
1897 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1898 : h->catalog_oldest_nonremovable));
1899 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1900 : h->data_oldest_nonremovable));
1901 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1902 : h->temp_oldest_nonremovable));
1903 : Assert(!TransactionIdIsValid(h->slot_xmin) ||
1904 : TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1905 : h->slot_xmin));
1906 : Assert(!TransactionIdIsValid(h->slot_catalog_xmin) ||
1907 : TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1908 : h->slot_catalog_xmin));
1909 :
1910 : /* update approximate horizons with the computed horizons */
1911 420090 : GlobalVisUpdateApply(h);
1912 420090 : }
1913 :
1914 : /*
1915 : * Determine what kind of visibility horizon needs to be used for a
1916 : * relation. If rel is NULL, the most conservative horizon is used.
1917 : */
1918 : static inline GlobalVisHorizonKind
1919 28875322 : GlobalVisHorizonKindForRel(Relation rel)
1920 : {
1921 : /*
1922 : * Other relkinds currently don't contain xids, nor always the necessary
1923 : * logical decoding markers.
1924 : */
1925 : Assert(!rel ||
1926 : rel->rd_rel->relkind == RELKIND_RELATION ||
1927 : rel->rd_rel->relkind == RELKIND_MATVIEW ||
1928 : rel->rd_rel->relkind == RELKIND_TOASTVALUE);
1929 :
1930 28875322 : if (rel == NULL || rel->rd_rel->relisshared || RecoveryInProgress())
1931 223600 : return VISHORIZON_SHARED;
1932 28651722 : else if (IsCatalogRelation(rel) ||
1933 22754000 : RelationIsAccessibleInLogicalDecoding(rel))
1934 5897730 : return VISHORIZON_CATALOG;
1935 22753992 : else if (!RELATION_IS_LOCAL(rel))
1936 22645652 : return VISHORIZON_DATA;
1937 : else
1938 108340 : return VISHORIZON_TEMP;
1939 : }
1940 :
1941 : /*
1942 : * Return the oldest XID for which deleted tuples must be preserved in the
1943 : * passed table.
1944 : *
1945 : * If rel is not NULL the horizon may be considerably more recent than
1946 : * otherwise (i.e. fewer tuples will be removable). In the NULL case a horizon
1947 : * that is correct (but not optimal) for all relations will be returned.
1948 : *
1949 : * This is used by VACUUM to decide which deleted tuples must be preserved in
1950 : * the passed in table.
1951 : */
1952 : TransactionId
1953 306170 : GetOldestNonRemovableTransactionId(Relation rel)
1954 : {
1955 : ComputeXidHorizonsResult horizons;
1956 :
1957 306170 : ComputeXidHorizons(&horizons);
1958 :
1959 306170 : switch (GlobalVisHorizonKindForRel(rel))
1960 : {
1961 47364 : case VISHORIZON_SHARED:
1962 47364 : return horizons.shared_oldest_nonremovable;
1963 189388 : case VISHORIZON_CATALOG:
1964 189388 : return horizons.catalog_oldest_nonremovable;
1965 44966 : case VISHORIZON_DATA:
1966 44966 : return horizons.data_oldest_nonremovable;
1967 24452 : case VISHORIZON_TEMP:
1968 24452 : return horizons.temp_oldest_nonremovable;
1969 : }
1970 :
1971 : /* just to prevent compiler warnings */
1972 0 : return InvalidTransactionId;
1973 : }
1974 :
1975 : /*
1976 : * Return the oldest transaction id any currently running backend might still
1977 : * consider running. This should not be used for visibility / pruning
1978 : * determinations (see GetOldestNonRemovableTransactionId()), but for
1979 : * decisions like up to where pg_subtrans can be truncated.
1980 : */
1981 : TransactionId
1982 3330 : GetOldestTransactionIdConsideredRunning(void)
1983 : {
1984 : ComputeXidHorizonsResult horizons;
1985 :
1986 3330 : ComputeXidHorizons(&horizons);
1987 :
1988 3330 : return horizons.oldest_considered_running;
1989 : }
1990 :
1991 : /*
1992 : * Return the visibility horizons for a hot standby feedback message.
1993 : */
1994 : void
1995 94 : GetReplicationHorizons(TransactionId *xmin, TransactionId *catalog_xmin)
1996 : {
1997 : ComputeXidHorizonsResult horizons;
1998 :
1999 94 : ComputeXidHorizons(&horizons);
2000 :
2001 : /*
2002 : * Don't want to use shared_oldest_nonremovable here, as that contains the
2003 : * effect of replication slot's catalog_xmin. We want to send a separate
2004 : * feedback for the catalog horizon, so the primary can remove data table
2005 : * contents more aggressively.
2006 : */
2007 94 : *xmin = horizons.shared_oldest_nonremovable_raw;
2008 94 : *catalog_xmin = horizons.slot_catalog_xmin;
2009 94 : }
2010 :
2011 : /*
2012 : * GetMaxSnapshotXidCount -- get max size for snapshot XID array
2013 : *
2014 : * We have to export this for use by snapmgr.c.
2015 : */
2016 : int
2017 64942 : GetMaxSnapshotXidCount(void)
2018 : {
2019 64942 : return procArray->maxProcs;
2020 : }
2021 :
2022 : /*
2023 : * GetMaxSnapshotSubxidCount -- get max size for snapshot sub-XID array
2024 : *
2025 : * We have to export this for use by snapmgr.c.
2026 : */
2027 : int
2028 64572 : GetMaxSnapshotSubxidCount(void)
2029 : {
2030 64572 : return TOTAL_MAX_CACHED_SUBXIDS;
2031 : }
2032 :
2033 : /*
2034 : * Helper function for GetSnapshotData() that checks if the bulk of the
2035 : * visibility information in the snapshot is still valid. If so, it updates
2036 : * the fields that need to change and returns true. Otherwise it returns
2037 : * false.
2038 : *
2039 : * This very likely can be evolved to not need ProcArrayLock held (at very
2040 : * least in the case we already hold a snapshot), but that's for another day.
2041 : */
2042 : static bool
2043 4322148 : GetSnapshotDataReuse(Snapshot snapshot)
2044 : {
2045 : uint64 curXactCompletionCount;
2046 :
2047 : Assert(LWLockHeldByMe(ProcArrayLock));
2048 :
2049 4322148 : if (unlikely(snapshot->snapXactCompletionCount == 0))
2050 64528 : return false;
2051 :
2052 4257620 : curXactCompletionCount = TransamVariables->xactCompletionCount;
2053 4257620 : if (curXactCompletionCount != snapshot->snapXactCompletionCount)
2054 699994 : return false;
2055 :
2056 : /*
2057 : * If the current xactCompletionCount is still the same as it was at the
2058 : * time the snapshot was built, we can be sure that rebuilding the
2059 : * contents of the snapshot the hard way would result in the same snapshot
2060 : * contents:
2061 : *
2062 : * As explained in transam/README, the set of xids considered running by
2063 : * GetSnapshotData() cannot change while ProcArrayLock is held. Snapshot
2064 : * contents only depend on transactions with xids and xactCompletionCount
2065 : * is incremented whenever a transaction with an xid finishes (while
2066 : * holding ProcArrayLock exclusively). Thus the xactCompletionCount check
2067 : * ensures we would detect if the snapshot would have changed.
2068 : *
2069 : * As the snapshot contents are the same as it was before, it is safe to
2070 : * re-enter the snapshot's xmin into the PGPROC array. None of the rows
2071 : * visible under the snapshot could already have been removed (that'd
2072 : * require the set of running transactions to change) and it fulfills the
2073 : * requirement that concurrent GetSnapshotData() calls yield the same
2074 : * xmin.
2075 : */
2076 3557626 : if (!TransactionIdIsValid(MyProc->xmin))
2077 1410618 : MyProc->xmin = TransactionXmin = snapshot->xmin;
2078 :
2079 3557626 : RecentXmin = snapshot->xmin;
2080 : Assert(TransactionIdPrecedesOrEquals(TransactionXmin, RecentXmin));
2081 :
2082 3557626 : snapshot->curcid = GetCurrentCommandId(false);
2083 3557626 : snapshot->active_count = 0;
2084 3557626 : snapshot->regd_count = 0;
2085 3557626 : snapshot->copied = false;
2086 :
2087 3557626 : return true;
2088 : }
2089 :
2090 : /*
2091 : * GetSnapshotData -- returns information about running transactions.
2092 : *
2093 : * The returned snapshot includes xmin (lowest still-running xact ID),
2094 : * xmax (highest completed xact ID + 1), and a list of running xact IDs
2095 : * in the range xmin <= xid < xmax. It is used as follows:
2096 : * All xact IDs < xmin are considered finished.
2097 : * All xact IDs >= xmax are considered still running.
2098 : * For an xact ID xmin <= xid < xmax, consult list to see whether
2099 : * it is considered running or not.
2100 : * This ensures that the set of transactions seen as "running" by the
2101 : * current xact will not change after it takes the snapshot.
2102 : *
2103 : * All running top-level XIDs are included in the snapshot, except for lazy
2104 : * VACUUM processes. We also try to include running subtransaction XIDs,
2105 : * but since PGPROC has only a limited cache area for subxact XIDs, full
2106 : * information may not be available. If we find any overflowed subxid arrays,
2107 : * we have to mark the snapshot's subxid data as overflowed, and extra work
2108 : * *may* need to be done to determine what's running (see XidInMVCCSnapshot()).
2109 : *
2110 : * We also update the following backend-global variables:
2111 : * TransactionXmin: the oldest xmin of any snapshot in use in the
2112 : * current transaction (this is the same as MyProc->xmin).
2113 : * RecentXmin: the xmin computed for the most recent snapshot. XIDs
2114 : * older than this are known not running any more.
2115 : *
2116 : * And try to advance the bounds of GlobalVis{Shared,Catalog,Data,Temp}Rels
2117 : * for the benefit of the GlobalVisTest* family of functions.
2118 : *
2119 : * Note: this function should probably not be called with an argument that's
2120 : * not statically allocated (see xip allocation below).
2121 : */
2122 : Snapshot
2123 4322148 : GetSnapshotData(Snapshot snapshot)
2124 : {
2125 4322148 : ProcArrayStruct *arrayP = procArray;
2126 4322148 : TransactionId *other_xids = ProcGlobal->xids;
2127 : TransactionId xmin;
2128 : TransactionId xmax;
2129 4322148 : int count = 0;
2130 4322148 : int subcount = 0;
2131 4322148 : bool suboverflowed = false;
2132 : FullTransactionId latest_completed;
2133 : TransactionId oldestxid;
2134 : int mypgxactoff;
2135 : TransactionId myxid;
2136 : uint64 curXactCompletionCount;
2137 :
2138 4322148 : TransactionId replication_slot_xmin = InvalidTransactionId;
2139 4322148 : TransactionId replication_slot_catalog_xmin = InvalidTransactionId;
2140 :
2141 : Assert(snapshot != NULL);
2142 :
2143 : /*
2144 : * Allocating space for maxProcs xids is usually overkill; numProcs would
2145 : * be sufficient. But it seems better to do the malloc while not holding
2146 : * the lock, so we can't look at numProcs. Likewise, we allocate much
2147 : * more subxip storage than is probably needed.
2148 : *
2149 : * This does open a possibility for avoiding repeated malloc/free: since
2150 : * maxProcs does not change at runtime, we can simply reuse the previous
2151 : * xip arrays if any. (This relies on the fact that all callers pass
2152 : * static SnapshotData structs.)
2153 : */
2154 4322148 : if (snapshot->xip == NULL)
2155 : {
2156 : /*
2157 : * First call for this snapshot. Snapshot is same size whether or not
2158 : * we are in recovery, see later comments.
2159 : */
2160 64516 : snapshot->xip = (TransactionId *)
2161 64516 : malloc(GetMaxSnapshotXidCount() * sizeof(TransactionId));
2162 64516 : if (snapshot->xip == NULL)
2163 0 : ereport(ERROR,
2164 : (errcode(ERRCODE_OUT_OF_MEMORY),
2165 : errmsg("out of memory")));
2166 : Assert(snapshot->subxip == NULL);
2167 64516 : snapshot->subxip = (TransactionId *)
2168 64516 : malloc(GetMaxSnapshotSubxidCount() * sizeof(TransactionId));
2169 64516 : if (snapshot->subxip == NULL)
2170 0 : ereport(ERROR,
2171 : (errcode(ERRCODE_OUT_OF_MEMORY),
2172 : errmsg("out of memory")));
2173 : }
2174 :
2175 : /*
2176 : * It is sufficient to get shared lock on ProcArrayLock, even if we are
2177 : * going to set MyProc->xmin.
2178 : */
2179 4322148 : LWLockAcquire(ProcArrayLock, LW_SHARED);
2180 :
2181 4322148 : if (GetSnapshotDataReuse(snapshot))
2182 : {
2183 3557626 : LWLockRelease(ProcArrayLock);
2184 3557626 : return snapshot;
2185 : }
2186 :
2187 764522 : latest_completed = TransamVariables->latestCompletedXid;
2188 764522 : mypgxactoff = MyProc->pgxactoff;
2189 764522 : myxid = other_xids[mypgxactoff];
2190 : Assert(myxid == MyProc->xid);
2191 :
2192 764522 : oldestxid = TransamVariables->oldestXid;
2193 764522 : curXactCompletionCount = TransamVariables->xactCompletionCount;
2194 :
2195 : /* xmax is always latestCompletedXid + 1 */
2196 764522 : xmax = XidFromFullTransactionId(latest_completed);
2197 764522 : TransactionIdAdvance(xmax);
2198 : Assert(TransactionIdIsNormal(xmax));
2199 :
2200 : /* initialize xmin calculation with xmax */
2201 764522 : xmin = xmax;
2202 :
2203 : /* take own xid into account, saves a check inside the loop */
2204 764522 : if (TransactionIdIsNormal(myxid) && NormalTransactionIdPrecedes(myxid, xmin))
2205 46838 : xmin = myxid;
2206 :
2207 764522 : snapshot->takenDuringRecovery = RecoveryInProgress();
2208 :
2209 764522 : if (!snapshot->takenDuringRecovery)
2210 : {
2211 762446 : int numProcs = arrayP->numProcs;
2212 762446 : TransactionId *xip = snapshot->xip;
2213 762446 : int *pgprocnos = arrayP->pgprocnos;
2214 762446 : XidCacheStatus *subxidStates = ProcGlobal->subxidStates;
2215 762446 : uint8 *allStatusFlags = ProcGlobal->statusFlags;
2216 :
2217 : /*
2218 : * First collect set of pgxactoff/xids that need to be included in the
2219 : * snapshot.
2220 : */
2221 6283714 : for (int pgxactoff = 0; pgxactoff < numProcs; pgxactoff++)
2222 : {
2223 : /* Fetch xid just once - see GetNewTransactionId */
2224 5521268 : TransactionId xid = UINT32_ACCESS_ONCE(other_xids[pgxactoff]);
2225 : uint8 statusFlags;
2226 :
2227 : Assert(allProcs[arrayP->pgprocnos[pgxactoff]].pgxactoff == pgxactoff);
2228 :
2229 : /*
2230 : * If the transaction has no XID assigned, we can skip it; it
2231 : * won't have sub-XIDs either.
2232 : */
2233 5521268 : if (likely(xid == InvalidTransactionId))
2234 4274230 : continue;
2235 :
2236 : /*
2237 : * We don't include our own XIDs (if any) in the snapshot. It
2238 : * needs to be included in the xmin computation, but we did so
2239 : * outside the loop.
2240 : */
2241 1247038 : if (pgxactoff == mypgxactoff)
2242 93226 : continue;
2243 :
2244 : /*
2245 : * The only way we are able to get here with a non-normal xid is
2246 : * during bootstrap - with this backend using
2247 : * BootstrapTransactionId. But the above test should filter that
2248 : * out.
2249 : */
2250 : Assert(TransactionIdIsNormal(xid));
2251 :
2252 : /*
2253 : * If the XID is >= xmax, we can skip it; such transactions will
2254 : * be treated as running anyway (and any sub-XIDs will also be >=
2255 : * xmax).
2256 : */
2257 1153812 : if (!NormalTransactionIdPrecedes(xid, xmax))
2258 248554 : continue;
2259 :
2260 : /*
2261 : * Skip over backends doing logical decoding which manages xmin
2262 : * separately (check below) and ones running LAZY VACUUM.
2263 : */
2264 905258 : statusFlags = allStatusFlags[pgxactoff];
2265 905258 : if (statusFlags & (PROC_IN_LOGICAL_DECODING | PROC_IN_VACUUM))
2266 116 : continue;
2267 :
2268 905142 : if (NormalTransactionIdPrecedes(xid, xmin))
2269 476964 : xmin = xid;
2270 :
2271 : /* Add XID to snapshot. */
2272 905142 : xip[count++] = xid;
2273 :
2274 : /*
2275 : * Save subtransaction XIDs if possible (if we've already
2276 : * overflowed, there's no point). Note that the subxact XIDs must
2277 : * be later than their parent, so no need to check them against
2278 : * xmin. We could filter against xmax, but it seems better not to
2279 : * do that much work while holding the ProcArrayLock.
2280 : *
2281 : * The other backend can add more subxids concurrently, but cannot
2282 : * remove any. Hence it's important to fetch nxids just once.
2283 : * Should be safe to use memcpy, though. (We needn't worry about
2284 : * missing any xids added concurrently, because they must postdate
2285 : * xmax.)
2286 : *
2287 : * Again, our own XIDs are not included in the snapshot.
2288 : */
2289 905142 : if (!suboverflowed)
2290 : {
2291 :
2292 905134 : if (subxidStates[pgxactoff].overflowed)
2293 1382 : suboverflowed = true;
2294 : else
2295 : {
2296 903752 : int nsubxids = subxidStates[pgxactoff].count;
2297 :
2298 903752 : if (nsubxids > 0)
2299 : {
2300 9630 : int pgprocno = pgprocnos[pgxactoff];
2301 9630 : PGPROC *proc = &allProcs[pgprocno];
2302 :
2303 9630 : pg_read_barrier(); /* pairs with GetNewTransactionId */
2304 :
2305 9630 : memcpy(snapshot->subxip + subcount,
2306 9630 : proc->subxids.xids,
2307 : nsubxids * sizeof(TransactionId));
2308 9630 : subcount += nsubxids;
2309 : }
2310 : }
2311 : }
2312 : }
2313 : }
2314 : else
2315 : {
2316 : /*
2317 : * We're in hot standby, so get XIDs from KnownAssignedXids.
2318 : *
2319 : * We store all xids directly into subxip[]. Here's why:
2320 : *
2321 : * In recovery we don't know which xids are top-level and which are
2322 : * subxacts, a design choice that greatly simplifies xid processing.
2323 : *
2324 : * It seems like we would want to try to put xids into xip[] only, but
2325 : * that is fairly small. We would either need to make that bigger or
2326 : * to increase the rate at which we WAL-log xid assignment; neither is
2327 : * an appealing choice.
2328 : *
2329 : * We could try to store xids into xip[] first and then into subxip[]
2330 : * if there are too many xids. That only works if the snapshot doesn't
2331 : * overflow because we do not search subxip[] in that case. A simpler
2332 : * way is to just store all xids in the subxip array because this is
2333 : * by far the bigger array. We just leave the xip array empty.
2334 : *
2335 : * Either way we need to change the way XidInMVCCSnapshot() works
2336 : * depending upon when the snapshot was taken, or change normal
2337 : * snapshot processing so it matches.
2338 : *
2339 : * Note: It is possible for recovery to end before we finish taking
2340 : * the snapshot, and for newly assigned transaction ids to be added to
2341 : * the ProcArray. xmax cannot change while we hold ProcArrayLock, so
2342 : * those newly added transaction ids would be filtered away, so we
2343 : * need not be concerned about them.
2344 : */
2345 2076 : subcount = KnownAssignedXidsGetAndSetXmin(snapshot->subxip, &xmin,
2346 : xmax);
2347 :
2348 2076 : if (TransactionIdPrecedesOrEquals(xmin, procArray->lastOverflowedXid))
2349 12 : suboverflowed = true;
2350 : }
2351 :
2352 :
2353 : /*
2354 : * Fetch into local variable while ProcArrayLock is held - the
2355 : * LWLockRelease below is a barrier, ensuring this happens inside the
2356 : * lock.
2357 : */
2358 764522 : replication_slot_xmin = procArray->replication_slot_xmin;
2359 764522 : replication_slot_catalog_xmin = procArray->replication_slot_catalog_xmin;
2360 :
2361 764522 : if (!TransactionIdIsValid(MyProc->xmin))
2362 419996 : MyProc->xmin = TransactionXmin = xmin;
2363 :
2364 764522 : LWLockRelease(ProcArrayLock);
2365 :
2366 : /* maintain state for GlobalVis* */
2367 : {
2368 : TransactionId def_vis_xid;
2369 : TransactionId def_vis_xid_data;
2370 : FullTransactionId def_vis_fxid;
2371 : FullTransactionId def_vis_fxid_data;
2372 : FullTransactionId oldestfxid;
2373 :
2374 : /*
2375 : * Converting oldestXid is only safe when xid horizon cannot advance,
2376 : * i.e. holding locks. While we don't hold the lock anymore, all the
2377 : * necessary data has been gathered with lock held.
2378 : */
2379 764522 : oldestfxid = FullXidRelativeTo(latest_completed, oldestxid);
2380 :
2381 : /* Check whether there's a replication slot requiring an older xmin. */
2382 : def_vis_xid_data =
2383 764522 : TransactionIdOlder(xmin, replication_slot_xmin);
2384 :
2385 : /*
2386 : * Rows in non-shared, non-catalog tables possibly could be vacuumed
2387 : * if older than this xid.
2388 : */
2389 764522 : def_vis_xid = def_vis_xid_data;
2390 :
2391 : /*
2392 : * Check whether there's a replication slot requiring an older catalog
2393 : * xmin.
2394 : */
2395 : def_vis_xid =
2396 764522 : TransactionIdOlder(replication_slot_catalog_xmin, def_vis_xid);
2397 :
2398 764522 : def_vis_fxid = FullXidRelativeTo(latest_completed, def_vis_xid);
2399 764522 : def_vis_fxid_data = FullXidRelativeTo(latest_completed, def_vis_xid_data);
2400 :
2401 : /*
2402 : * Check if we can increase upper bound. As a previous
2403 : * GlobalVisUpdate() might have computed more aggressive values, don't
2404 : * overwrite them if so.
2405 : */
2406 : GlobalVisSharedRels.definitely_needed =
2407 764522 : FullTransactionIdNewer(def_vis_fxid,
2408 : GlobalVisSharedRels.definitely_needed);
2409 : GlobalVisCatalogRels.definitely_needed =
2410 764522 : FullTransactionIdNewer(def_vis_fxid,
2411 : GlobalVisCatalogRels.definitely_needed);
2412 : GlobalVisDataRels.definitely_needed =
2413 764522 : FullTransactionIdNewer(def_vis_fxid_data,
2414 : GlobalVisDataRels.definitely_needed);
2415 : /* See temp_oldest_nonremovable computation in ComputeXidHorizons() */
2416 764522 : if (TransactionIdIsNormal(myxid))
2417 : GlobalVisTempRels.definitely_needed =
2418 93022 : FullXidRelativeTo(latest_completed, myxid);
2419 : else
2420 : {
2421 671500 : GlobalVisTempRels.definitely_needed = latest_completed;
2422 671500 : FullTransactionIdAdvance(&GlobalVisTempRels.definitely_needed);
2423 : }
2424 :
2425 : /*
2426 : * Check if we know that we can initialize or increase the lower
2427 : * bound. Currently the only cheap way to do so is to use
2428 : * TransamVariables->oldestXid as input.
2429 : *
2430 : * We should definitely be able to do better. We could e.g. put a
2431 : * global lower bound value into TransamVariables.
2432 : */
2433 : GlobalVisSharedRels.maybe_needed =
2434 764522 : FullTransactionIdNewer(GlobalVisSharedRels.maybe_needed,
2435 : oldestfxid);
2436 : GlobalVisCatalogRels.maybe_needed =
2437 764522 : FullTransactionIdNewer(GlobalVisCatalogRels.maybe_needed,
2438 : oldestfxid);
2439 : GlobalVisDataRels.maybe_needed =
2440 764522 : FullTransactionIdNewer(GlobalVisDataRels.maybe_needed,
2441 : oldestfxid);
2442 : /* accurate value known */
2443 764522 : GlobalVisTempRels.maybe_needed = GlobalVisTempRels.definitely_needed;
2444 : }
2445 :
2446 764522 : RecentXmin = xmin;
2447 : Assert(TransactionIdPrecedesOrEquals(TransactionXmin, RecentXmin));
2448 :
2449 764522 : snapshot->xmin = xmin;
2450 764522 : snapshot->xmax = xmax;
2451 764522 : snapshot->xcnt = count;
2452 764522 : snapshot->subxcnt = subcount;
2453 764522 : snapshot->suboverflowed = suboverflowed;
2454 764522 : snapshot->snapXactCompletionCount = curXactCompletionCount;
2455 :
2456 764522 : snapshot->curcid = GetCurrentCommandId(false);
2457 :
2458 : /*
2459 : * This is a new snapshot, so set both refcounts are zero, and mark it as
2460 : * not copied in persistent memory.
2461 : */
2462 764522 : snapshot->active_count = 0;
2463 764522 : snapshot->regd_count = 0;
2464 764522 : snapshot->copied = false;
2465 :
2466 764522 : return snapshot;
2467 : }
2468 :
2469 : /*
2470 : * ProcArrayInstallImportedXmin -- install imported xmin into MyProc->xmin
2471 : *
2472 : * This is called when installing a snapshot imported from another
2473 : * transaction. To ensure that OldestXmin doesn't go backwards, we must
2474 : * check that the source transaction is still running, and we'd better do
2475 : * that atomically with installing the new xmin.
2476 : *
2477 : * Returns true if successful, false if source xact is no longer running.
2478 : */
2479 : bool
2480 36 : ProcArrayInstallImportedXmin(TransactionId xmin,
2481 : VirtualTransactionId *sourcevxid)
2482 : {
2483 36 : bool result = false;
2484 36 : ProcArrayStruct *arrayP = procArray;
2485 : int index;
2486 :
2487 : Assert(TransactionIdIsNormal(xmin));
2488 36 : if (!sourcevxid)
2489 0 : return false;
2490 :
2491 : /* Get lock so source xact can't end while we're doing this */
2492 36 : LWLockAcquire(ProcArrayLock, LW_SHARED);
2493 :
2494 : /*
2495 : * Find the PGPROC entry of the source transaction. (This could use
2496 : * GetPGProcByNumber(), unless it's a prepared xact. But this isn't
2497 : * performance critical.)
2498 : */
2499 36 : for (index = 0; index < arrayP->numProcs; index++)
2500 : {
2501 36 : int pgprocno = arrayP->pgprocnos[index];
2502 36 : PGPROC *proc = &allProcs[pgprocno];
2503 36 : int statusFlags = ProcGlobal->statusFlags[index];
2504 : TransactionId xid;
2505 :
2506 : /* Ignore procs running LAZY VACUUM */
2507 36 : if (statusFlags & PROC_IN_VACUUM)
2508 0 : continue;
2509 :
2510 : /* We are only interested in the specific virtual transaction. */
2511 36 : if (proc->vxid.procNumber != sourcevxid->procNumber)
2512 0 : continue;
2513 36 : if (proc->vxid.lxid != sourcevxid->localTransactionId)
2514 0 : continue;
2515 :
2516 : /*
2517 : * We check the transaction's database ID for paranoia's sake: if it's
2518 : * in another DB then its xmin does not cover us. Caller should have
2519 : * detected this already, so we just treat any funny cases as
2520 : * "transaction not found".
2521 : */
2522 36 : if (proc->databaseId != MyDatabaseId)
2523 0 : continue;
2524 :
2525 : /*
2526 : * Likewise, let's just make real sure its xmin does cover us.
2527 : */
2528 36 : xid = UINT32_ACCESS_ONCE(proc->xmin);
2529 36 : if (!TransactionIdIsNormal(xid) ||
2530 36 : !TransactionIdPrecedesOrEquals(xid, xmin))
2531 0 : continue;
2532 :
2533 : /*
2534 : * We're good. Install the new xmin. As in GetSnapshotData, set
2535 : * TransactionXmin too. (Note that because snapmgr.c called
2536 : * GetSnapshotData first, we'll be overwriting a valid xmin here, so
2537 : * we don't check that.)
2538 : */
2539 36 : MyProc->xmin = TransactionXmin = xmin;
2540 :
2541 36 : result = true;
2542 36 : break;
2543 : }
2544 :
2545 36 : LWLockRelease(ProcArrayLock);
2546 :
2547 36 : return result;
2548 : }
2549 :
2550 : /*
2551 : * ProcArrayInstallRestoredXmin -- install restored xmin into MyProc->xmin
2552 : *
2553 : * This is like ProcArrayInstallImportedXmin, but we have a pointer to the
2554 : * PGPROC of the transaction from which we imported the snapshot, rather than
2555 : * an XID.
2556 : *
2557 : * Note that this function also copies statusFlags from the source `proc` in
2558 : * order to avoid the case where MyProc's xmin needs to be skipped for
2559 : * computing xid horizon.
2560 : *
2561 : * Returns true if successful, false if source xact is no longer running.
2562 : */
2563 : bool
2564 3122 : ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
2565 : {
2566 3122 : bool result = false;
2567 : TransactionId xid;
2568 :
2569 : Assert(TransactionIdIsNormal(xmin));
2570 : Assert(proc != NULL);
2571 :
2572 : /*
2573 : * Get an exclusive lock so that we can copy statusFlags from source proc.
2574 : */
2575 3122 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
2576 :
2577 : /*
2578 : * Be certain that the referenced PGPROC has an advertised xmin which is
2579 : * no later than the one we're installing, so that the system-wide xmin
2580 : * can't go backwards. Also, make sure it's running in the same database,
2581 : * so that the per-database xmin cannot go backwards.
2582 : */
2583 3122 : xid = UINT32_ACCESS_ONCE(proc->xmin);
2584 3122 : if (proc->databaseId == MyDatabaseId &&
2585 3122 : TransactionIdIsNormal(xid) &&
2586 3122 : TransactionIdPrecedesOrEquals(xid, xmin))
2587 : {
2588 : /*
2589 : * Install xmin and propagate the statusFlags that affect how the
2590 : * value is interpreted by vacuum.
2591 : */
2592 3122 : MyProc->xmin = TransactionXmin = xmin;
2593 3122 : MyProc->statusFlags = (MyProc->statusFlags & ~PROC_XMIN_FLAGS) |
2594 3122 : (proc->statusFlags & PROC_XMIN_FLAGS);
2595 3122 : ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
2596 :
2597 3122 : result = true;
2598 : }
2599 :
2600 3122 : LWLockRelease(ProcArrayLock);
2601 :
2602 3122 : return result;
2603 : }
2604 :
2605 : /*
2606 : * GetRunningTransactionData -- returns information about running transactions.
2607 : *
2608 : * Similar to GetSnapshotData but returns more information. We include
2609 : * all PGPROCs with an assigned TransactionId, even VACUUM processes and
2610 : * prepared transactions.
2611 : *
2612 : * We acquire XidGenLock and ProcArrayLock, but the caller is responsible for
2613 : * releasing them. Acquiring XidGenLock ensures that no new XIDs enter the proc
2614 : * array until the caller has WAL-logged this snapshot, and releases the
2615 : * lock. Acquiring ProcArrayLock ensures that no transactions commit until the
2616 : * lock is released.
2617 : *
2618 : * The returned data structure is statically allocated; caller should not
2619 : * modify it, and must not assume it is valid past the next call.
2620 : *
2621 : * This is never executed during recovery so there is no need to look at
2622 : * KnownAssignedXids.
2623 : *
2624 : * Dummy PGPROCs from prepared transaction are included, meaning that this
2625 : * may return entries with duplicated TransactionId values coming from
2626 : * transaction finishing to prepare. Nothing is done about duplicated
2627 : * entries here to not hold on ProcArrayLock more than necessary.
2628 : *
2629 : * We don't worry about updating other counters, we want to keep this as
2630 : * simple as possible and leave GetSnapshotData() as the primary code for
2631 : * that bookkeeping.
2632 : *
2633 : * Note that if any transaction has overflowed its cached subtransactions
2634 : * then there is no real need include any subtransactions.
2635 : */
2636 : RunningTransactions
2637 2746 : GetRunningTransactionData(void)
2638 : {
2639 : /* result workspace */
2640 : static RunningTransactionsData CurrentRunningXactsData;
2641 :
2642 2746 : ProcArrayStruct *arrayP = procArray;
2643 2746 : TransactionId *other_xids = ProcGlobal->xids;
2644 2746 : RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
2645 : TransactionId latestCompletedXid;
2646 : TransactionId oldestRunningXid;
2647 : TransactionId oldestDatabaseRunningXid;
2648 : TransactionId *xids;
2649 : int index;
2650 : int count;
2651 : int subcount;
2652 : bool suboverflowed;
2653 :
2654 : Assert(!RecoveryInProgress());
2655 :
2656 : /*
2657 : * Allocating space for maxProcs xids is usually overkill; numProcs would
2658 : * be sufficient. But it seems better to do the malloc while not holding
2659 : * the lock, so we can't look at numProcs. Likewise, we allocate much
2660 : * more subxip storage than is probably needed.
2661 : *
2662 : * Should only be allocated in bgwriter, since only ever executed during
2663 : * checkpoints.
2664 : */
2665 2746 : if (CurrentRunningXacts->xids == NULL)
2666 : {
2667 : /*
2668 : * First call
2669 : */
2670 1052 : CurrentRunningXacts->xids = (TransactionId *)
2671 1052 : malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
2672 1052 : if (CurrentRunningXacts->xids == NULL)
2673 0 : ereport(ERROR,
2674 : (errcode(ERRCODE_OUT_OF_MEMORY),
2675 : errmsg("out of memory")));
2676 : }
2677 :
2678 2746 : xids = CurrentRunningXacts->xids;
2679 :
2680 2746 : count = subcount = 0;
2681 2746 : suboverflowed = false;
2682 :
2683 : /*
2684 : * Ensure that no xids enter or leave the procarray while we obtain
2685 : * snapshot.
2686 : */
2687 2746 : LWLockAcquire(ProcArrayLock, LW_SHARED);
2688 2746 : LWLockAcquire(XidGenLock, LW_SHARED);
2689 :
2690 2746 : latestCompletedXid =
2691 2746 : XidFromFullTransactionId(TransamVariables->latestCompletedXid);
2692 2746 : oldestDatabaseRunningXid = oldestRunningXid =
2693 2746 : XidFromFullTransactionId(TransamVariables->nextXid);
2694 :
2695 : /*
2696 : * Spin over procArray collecting all xids
2697 : */
2698 13264 : for (index = 0; index < arrayP->numProcs; index++)
2699 : {
2700 : TransactionId xid;
2701 :
2702 : /* Fetch xid just once - see GetNewTransactionId */
2703 10518 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
2704 :
2705 : /*
2706 : * We don't need to store transactions that don't have a TransactionId
2707 : * yet because they will not show as running on a standby server.
2708 : */
2709 10518 : if (!TransactionIdIsValid(xid))
2710 8858 : continue;
2711 :
2712 : /*
2713 : * Be careful not to exclude any xids before calculating the values of
2714 : * oldestRunningXid and suboverflowed, since these are used to clean
2715 : * up transaction information held on standbys.
2716 : */
2717 1660 : if (TransactionIdPrecedes(xid, oldestRunningXid))
2718 1192 : oldestRunningXid = xid;
2719 :
2720 : /*
2721 : * Also, update the oldest running xid within the current database. As
2722 : * fetching pgprocno and PGPROC could cause cache misses, we do cheap
2723 : * TransactionId comparison first.
2724 : */
2725 1660 : if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
2726 : {
2727 1660 : int pgprocno = arrayP->pgprocnos[index];
2728 1660 : PGPROC *proc = &allProcs[pgprocno];
2729 :
2730 1660 : if (proc->databaseId == MyDatabaseId)
2731 426 : oldestDatabaseRunningXid = xid;
2732 : }
2733 :
2734 1660 : if (ProcGlobal->subxidStates[index].overflowed)
2735 4 : suboverflowed = true;
2736 :
2737 : /*
2738 : * If we wished to exclude xids this would be the right place for it.
2739 : * Procs with the PROC_IN_VACUUM flag set don't usually assign xids,
2740 : * but they do during truncation at the end when they get the lock and
2741 : * truncate, so it is not much of a problem to include them if they
2742 : * are seen and it is cleaner to include them.
2743 : */
2744 :
2745 1660 : xids[count++] = xid;
2746 : }
2747 :
2748 : /*
2749 : * Spin over procArray collecting all subxids, but only if there hasn't
2750 : * been a suboverflow.
2751 : */
2752 2746 : if (!suboverflowed)
2753 : {
2754 2742 : XidCacheStatus *other_subxidstates = ProcGlobal->subxidStates;
2755 :
2756 13248 : for (index = 0; index < arrayP->numProcs; index++)
2757 : {
2758 10506 : int pgprocno = arrayP->pgprocnos[index];
2759 10506 : PGPROC *proc = &allProcs[pgprocno];
2760 : int nsubxids;
2761 :
2762 : /*
2763 : * Save subtransaction XIDs. Other backends can't add or remove
2764 : * entries while we're holding XidGenLock.
2765 : */
2766 10506 : nsubxids = other_subxidstates[index].count;
2767 10506 : if (nsubxids > 0)
2768 : {
2769 : /* barrier not really required, as XidGenLock is held, but ... */
2770 28 : pg_read_barrier(); /* pairs with GetNewTransactionId */
2771 :
2772 28 : memcpy(&xids[count], proc->subxids.xids,
2773 : nsubxids * sizeof(TransactionId));
2774 28 : count += nsubxids;
2775 28 : subcount += nsubxids;
2776 :
2777 : /*
2778 : * Top-level XID of a transaction is always less than any of
2779 : * its subxids, so we don't need to check if any of the
2780 : * subxids are smaller than oldestRunningXid
2781 : */
2782 : }
2783 : }
2784 : }
2785 :
2786 : /*
2787 : * It's important *not* to include the limits set by slots here because
2788 : * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
2789 : * were to be included here the initial value could never increase because
2790 : * of a circular dependency where slots only increase their limits when
2791 : * running xacts increases oldestRunningXid and running xacts only
2792 : * increases if slots do.
2793 : */
2794 :
2795 2746 : CurrentRunningXacts->xcnt = count - subcount;
2796 2746 : CurrentRunningXacts->subxcnt = subcount;
2797 2746 : CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
2798 2746 : CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
2799 2746 : CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
2800 2746 : CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
2801 2746 : CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
2802 :
2803 : Assert(TransactionIdIsValid(CurrentRunningXacts->nextXid));
2804 : Assert(TransactionIdIsValid(CurrentRunningXacts->oldestRunningXid));
2805 : Assert(TransactionIdIsNormal(CurrentRunningXacts->latestCompletedXid));
2806 :
2807 : /* We don't release the locks here, the caller is responsible for that */
2808 :
2809 2746 : return CurrentRunningXacts;
2810 : }
2811 :
2812 : /*
2813 : * GetOldestActiveTransactionId()
2814 : *
2815 : * Similar to GetSnapshotData but returns just oldestActiveXid. We include
2816 : * all PGPROCs with an assigned TransactionId, even VACUUM processes.
2817 : *
2818 : * If allDbs is true, we look at all databases, though there is no need to
2819 : * include WALSender since this has no effect on hot standby conflicts. If
2820 : * allDbs is false, skip processes attached to other databases.
2821 : *
2822 : * This is never executed during recovery so there is no need to look at
2823 : * KnownAssignedXids.
2824 : *
2825 : * We don't worry about updating other counters, we want to keep this as
2826 : * simple as possible and leave GetSnapshotData() as the primary code for
2827 : * that bookkeeping.
2828 : *
2829 : * inCommitOnly indicates getting the oldestActiveXid among the transactions
2830 : * in the commit critical section.
2831 : */
2832 : TransactionId
2833 4396 : GetOldestActiveTransactionId(bool inCommitOnly, bool allDbs)
2834 : {
2835 4396 : ProcArrayStruct *arrayP = procArray;
2836 4396 : TransactionId *other_xids = ProcGlobal->xids;
2837 : TransactionId oldestRunningXid;
2838 : int index;
2839 :
2840 : Assert(!RecoveryInProgress());
2841 :
2842 : /*
2843 : * Read nextXid, as the upper bound of what's still active.
2844 : *
2845 : * Reading a TransactionId is atomic, but we must grab the lock to make
2846 : * sure that all XIDs < nextXid are already present in the proc array (or
2847 : * have already completed), when we spin over it.
2848 : */
2849 4396 : LWLockAcquire(XidGenLock, LW_SHARED);
2850 4396 : oldestRunningXid = XidFromFullTransactionId(TransamVariables->nextXid);
2851 4396 : LWLockRelease(XidGenLock);
2852 :
2853 : /*
2854 : * Spin over procArray collecting all xids and subxids.
2855 : */
2856 4396 : LWLockAcquire(ProcArrayLock, LW_SHARED);
2857 21344 : for (index = 0; index < arrayP->numProcs; index++)
2858 : {
2859 : TransactionId xid;
2860 16948 : int pgprocno = arrayP->pgprocnos[index];
2861 16948 : PGPROC *proc = &allProcs[pgprocno];
2862 :
2863 : /* Fetch xid just once - see GetNewTransactionId */
2864 16948 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
2865 :
2866 16948 : if (!TransactionIdIsNormal(xid))
2867 12718 : continue;
2868 :
2869 4230 : if (inCommitOnly &&
2870 2592 : (proc->delayChkptFlags & DELAY_CHKPT_IN_COMMIT) == 0)
2871 2 : continue;
2872 :
2873 4228 : if (!allDbs && proc->databaseId != MyDatabaseId)
2874 0 : continue;
2875 :
2876 4228 : if (TransactionIdPrecedes(xid, oldestRunningXid))
2877 3724 : oldestRunningXid = xid;
2878 :
2879 : /*
2880 : * Top-level XID of a transaction is always less than any of its
2881 : * subxids, so we don't need to check if any of the subxids are
2882 : * smaller than oldestRunningXid
2883 : */
2884 : }
2885 4396 : LWLockRelease(ProcArrayLock);
2886 :
2887 4396 : return oldestRunningXid;
2888 : }
2889 :
2890 : /*
2891 : * GetOldestSafeDecodingTransactionId -- lowest xid not affected by vacuum
2892 : *
2893 : * Returns the oldest xid that we can guarantee not to have been affected by
2894 : * vacuum, i.e. no rows >= that xid have been vacuumed away unless the
2895 : * transaction aborted. Note that the value can (and most of the time will) be
2896 : * much more conservative than what really has been affected by vacuum, but we
2897 : * currently don't have better data available.
2898 : *
2899 : * This is useful to initialize the cutoff xid after which a new changeset
2900 : * extraction replication slot can start decoding changes.
2901 : *
2902 : * Must be called with ProcArrayLock held either shared or exclusively,
2903 : * although most callers will want to use exclusive mode since it is expected
2904 : * that the caller will immediately use the xid to peg the xmin horizon.
2905 : */
2906 : TransactionId
2907 1314 : GetOldestSafeDecodingTransactionId(bool catalogOnly)
2908 : {
2909 1314 : ProcArrayStruct *arrayP = procArray;
2910 : TransactionId oldestSafeXid;
2911 : int index;
2912 1314 : bool recovery_in_progress = RecoveryInProgress();
2913 :
2914 : Assert(LWLockHeldByMe(ProcArrayLock));
2915 :
2916 : /*
2917 : * Acquire XidGenLock, so no transactions can acquire an xid while we're
2918 : * running. If no transaction with xid were running concurrently a new xid
2919 : * could influence the RecentXmin et al.
2920 : *
2921 : * We initialize the computation to nextXid since that's guaranteed to be
2922 : * a safe, albeit pessimal, value.
2923 : */
2924 1314 : LWLockAcquire(XidGenLock, LW_SHARED);
2925 1314 : oldestSafeXid = XidFromFullTransactionId(TransamVariables->nextXid);
2926 :
2927 : /*
2928 : * If there's already a slot pegging the xmin horizon, we can start with
2929 : * that value, it's guaranteed to be safe since it's computed by this
2930 : * routine initially and has been enforced since. We can always use the
2931 : * slot's general xmin horizon, but the catalog horizon is only usable
2932 : * when only catalog data is going to be looked at.
2933 : */
2934 1734 : if (TransactionIdIsValid(procArray->replication_slot_xmin) &&
2935 420 : TransactionIdPrecedes(procArray->replication_slot_xmin,
2936 : oldestSafeXid))
2937 24 : oldestSafeXid = procArray->replication_slot_xmin;
2938 :
2939 1314 : if (catalogOnly &&
2940 662 : TransactionIdIsValid(procArray->replication_slot_catalog_xmin) &&
2941 134 : TransactionIdPrecedes(procArray->replication_slot_catalog_xmin,
2942 : oldestSafeXid))
2943 52 : oldestSafeXid = procArray->replication_slot_catalog_xmin;
2944 :
2945 : /*
2946 : * If we're not in recovery, we walk over the procarray and collect the
2947 : * lowest xid. Since we're called with ProcArrayLock held and have
2948 : * acquired XidGenLock, no entries can vanish concurrently, since
2949 : * ProcGlobal->xids[i] is only set with XidGenLock held and only cleared
2950 : * with ProcArrayLock held.
2951 : *
2952 : * In recovery we can't lower the safe value besides what we've computed
2953 : * above, so we'll have to wait a bit longer there. We unfortunately can
2954 : * *not* use KnownAssignedXidsGetOldestXmin() since the KnownAssignedXids
2955 : * machinery can miss values and return an older value than is safe.
2956 : */
2957 1314 : if (!recovery_in_progress)
2958 : {
2959 1258 : TransactionId *other_xids = ProcGlobal->xids;
2960 :
2961 : /*
2962 : * Spin over procArray collecting min(ProcGlobal->xids[i])
2963 : */
2964 6434 : for (index = 0; index < arrayP->numProcs; index++)
2965 : {
2966 : TransactionId xid;
2967 :
2968 : /* Fetch xid just once - see GetNewTransactionId */
2969 5176 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
2970 :
2971 5176 : if (!TransactionIdIsNormal(xid))
2972 5156 : continue;
2973 :
2974 20 : if (TransactionIdPrecedes(xid, oldestSafeXid))
2975 16 : oldestSafeXid = xid;
2976 : }
2977 : }
2978 :
2979 1314 : LWLockRelease(XidGenLock);
2980 :
2981 1314 : return oldestSafeXid;
2982 : }
2983 :
2984 : /*
2985 : * GetVirtualXIDsDelayingChkpt -- Get the VXIDs of transactions that are
2986 : * delaying checkpoint because they have critical actions in progress.
2987 : *
2988 : * Constructs an array of VXIDs of transactions that are currently in commit
2989 : * critical sections, as shown by having specified delayChkptFlags bits set
2990 : * in their PGPROC.
2991 : *
2992 : * Returns a palloc'd array that should be freed by the caller.
2993 : * *nvxids is the number of valid entries.
2994 : *
2995 : * Note that because backends set or clear delayChkptFlags without holding any
2996 : * lock, the result is somewhat indeterminate, but we don't really care. Even
2997 : * in a multiprocessor with delayed writes to shared memory, it should be
2998 : * certain that setting of delayChkptFlags will propagate to shared memory
2999 : * when the backend takes a lock, so we cannot fail to see a virtual xact as
3000 : * delayChkptFlags if it's already inserted its commit record. Whether it
3001 : * takes a little while for clearing of delayChkptFlags to propagate is
3002 : * unimportant for correctness.
3003 : */
3004 : VirtualTransactionId *
3005 6004 : GetVirtualXIDsDelayingChkpt(int *nvxids, int type)
3006 : {
3007 : VirtualTransactionId *vxids;
3008 6004 : ProcArrayStruct *arrayP = procArray;
3009 6004 : int count = 0;
3010 : int index;
3011 :
3012 : Assert(type != 0);
3013 :
3014 : /* allocate what's certainly enough result space */
3015 : vxids = (VirtualTransactionId *)
3016 6004 : palloc(sizeof(VirtualTransactionId) * arrayP->maxProcs);
3017 :
3018 6004 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3019 :
3020 19984 : for (index = 0; index < arrayP->numProcs; index++)
3021 : {
3022 13980 : int pgprocno = arrayP->pgprocnos[index];
3023 13980 : PGPROC *proc = &allProcs[pgprocno];
3024 :
3025 13980 : if ((proc->delayChkptFlags & type) != 0)
3026 : {
3027 : VirtualTransactionId vxid;
3028 :
3029 92 : GET_VXID_FROM_PGPROC(vxid, *proc);
3030 92 : if (VirtualTransactionIdIsValid(vxid))
3031 92 : vxids[count++] = vxid;
3032 : }
3033 : }
3034 :
3035 6004 : LWLockRelease(ProcArrayLock);
3036 :
3037 6004 : *nvxids = count;
3038 6004 : return vxids;
3039 : }
3040 :
3041 : /*
3042 : * HaveVirtualXIDsDelayingChkpt -- Are any of the specified VXIDs delaying?
3043 : *
3044 : * This is used with the results of GetVirtualXIDsDelayingChkpt to see if any
3045 : * of the specified VXIDs are still in critical sections of code.
3046 : *
3047 : * Note: this is O(N^2) in the number of vxacts that are/were delaying, but
3048 : * those numbers should be small enough for it not to be a problem.
3049 : */
3050 : bool
3051 96 : HaveVirtualXIDsDelayingChkpt(VirtualTransactionId *vxids, int nvxids, int type)
3052 : {
3053 96 : bool result = false;
3054 96 : ProcArrayStruct *arrayP = procArray;
3055 : int index;
3056 :
3057 : Assert(type != 0);
3058 :
3059 96 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3060 :
3061 910 : for (index = 0; index < arrayP->numProcs; index++)
3062 : {
3063 832 : int pgprocno = arrayP->pgprocnos[index];
3064 832 : PGPROC *proc = &allProcs[pgprocno];
3065 : VirtualTransactionId vxid;
3066 :
3067 832 : GET_VXID_FROM_PGPROC(vxid, *proc);
3068 :
3069 832 : if ((proc->delayChkptFlags & type) != 0 &&
3070 50 : VirtualTransactionIdIsValid(vxid))
3071 : {
3072 : int i;
3073 :
3074 90 : for (i = 0; i < nvxids; i++)
3075 : {
3076 58 : if (VirtualTransactionIdEquals(vxid, vxids[i]))
3077 : {
3078 18 : result = true;
3079 18 : break;
3080 : }
3081 : }
3082 50 : if (result)
3083 18 : break;
3084 : }
3085 : }
3086 :
3087 96 : LWLockRelease(ProcArrayLock);
3088 :
3089 96 : return result;
3090 : }
3091 :
3092 : /*
3093 : * ProcNumberGetProc -- get a backend's PGPROC given its proc number
3094 : *
3095 : * The result may be out of date arbitrarily quickly, so the caller
3096 : * must be careful about how this information is used. NULL is
3097 : * returned if the backend is not active.
3098 : */
3099 : PGPROC *
3100 1098 : ProcNumberGetProc(ProcNumber procNumber)
3101 : {
3102 : PGPROC *result;
3103 :
3104 1098 : if (procNumber < 0 || procNumber >= ProcGlobal->allProcCount)
3105 2 : return NULL;
3106 1096 : result = GetPGProcByNumber(procNumber);
3107 :
3108 1096 : if (result->pid == 0)
3109 6 : return NULL;
3110 :
3111 1090 : return result;
3112 : }
3113 :
3114 : /*
3115 : * ProcNumberGetTransactionIds -- get a backend's transaction status
3116 : *
3117 : * Get the xid, xmin, nsubxid and overflow status of the backend. The
3118 : * result may be out of date arbitrarily quickly, so the caller must be
3119 : * careful about how this information is used.
3120 : */
3121 : void
3122 20792 : ProcNumberGetTransactionIds(ProcNumber procNumber, TransactionId *xid,
3123 : TransactionId *xmin, int *nsubxid, bool *overflowed)
3124 : {
3125 : PGPROC *proc;
3126 :
3127 20792 : *xid = InvalidTransactionId;
3128 20792 : *xmin = InvalidTransactionId;
3129 20792 : *nsubxid = 0;
3130 20792 : *overflowed = false;
3131 :
3132 20792 : if (procNumber < 0 || procNumber >= ProcGlobal->allProcCount)
3133 0 : return;
3134 20792 : proc = GetPGProcByNumber(procNumber);
3135 :
3136 : /* Need to lock out additions/removals of backends */
3137 20792 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3138 :
3139 20792 : if (proc->pid != 0)
3140 : {
3141 20792 : *xid = proc->xid;
3142 20792 : *xmin = proc->xmin;
3143 20792 : *nsubxid = proc->subxidStatus.count;
3144 20792 : *overflowed = proc->subxidStatus.overflowed;
3145 : }
3146 :
3147 20792 : LWLockRelease(ProcArrayLock);
3148 : }
3149 :
3150 : /*
3151 : * BackendPidGetProc -- get a backend's PGPROC given its PID
3152 : *
3153 : * Returns NULL if not found. Note that it is up to the caller to be
3154 : * sure that the question remains meaningful for long enough for the
3155 : * answer to be used ...
3156 : */
3157 : PGPROC *
3158 22782 : BackendPidGetProc(int pid)
3159 : {
3160 : PGPROC *result;
3161 :
3162 22782 : if (pid == 0) /* never match dummy PGPROCs */
3163 6 : return NULL;
3164 :
3165 22776 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3166 :
3167 22776 : result = BackendPidGetProcWithLock(pid);
3168 :
3169 22776 : LWLockRelease(ProcArrayLock);
3170 :
3171 22776 : return result;
3172 : }
3173 :
3174 : /*
3175 : * BackendPidGetProcWithLock -- get a backend's PGPROC given its PID
3176 : *
3177 : * Same as above, except caller must be holding ProcArrayLock. The found
3178 : * entry, if any, can be assumed to be valid as long as the lock remains held.
3179 : */
3180 : PGPROC *
3181 26158 : BackendPidGetProcWithLock(int pid)
3182 : {
3183 26158 : PGPROC *result = NULL;
3184 26158 : ProcArrayStruct *arrayP = procArray;
3185 : int index;
3186 :
3187 26158 : if (pid == 0) /* never match dummy PGPROCs */
3188 0 : return NULL;
3189 :
3190 102850 : for (index = 0; index < arrayP->numProcs; index++)
3191 : {
3192 91372 : PGPROC *proc = &allProcs[arrayP->pgprocnos[index]];
3193 :
3194 91372 : if (proc->pid == pid)
3195 : {
3196 14680 : result = proc;
3197 14680 : break;
3198 : }
3199 : }
3200 :
3201 26158 : return result;
3202 : }
3203 :
3204 : /*
3205 : * BackendXidGetPid -- get a backend's pid given its XID
3206 : *
3207 : * Returns 0 if not found or it's a prepared transaction. Note that
3208 : * it is up to the caller to be sure that the question remains
3209 : * meaningful for long enough for the answer to be used ...
3210 : *
3211 : * Only main transaction Ids are considered. This function is mainly
3212 : * useful for determining what backend owns a lock.
3213 : *
3214 : * Beware that not every xact has an XID assigned. However, as long as you
3215 : * only call this using an XID found on disk, you're safe.
3216 : */
3217 : int
3218 60 : BackendXidGetPid(TransactionId xid)
3219 : {
3220 60 : int result = 0;
3221 60 : ProcArrayStruct *arrayP = procArray;
3222 60 : TransactionId *other_xids = ProcGlobal->xids;
3223 : int index;
3224 :
3225 60 : if (xid == InvalidTransactionId) /* never match invalid xid */
3226 0 : return 0;
3227 :
3228 60 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3229 :
3230 184 : for (index = 0; index < arrayP->numProcs; index++)
3231 : {
3232 168 : if (other_xids[index] == xid)
3233 : {
3234 44 : int pgprocno = arrayP->pgprocnos[index];
3235 44 : PGPROC *proc = &allProcs[pgprocno];
3236 :
3237 44 : result = proc->pid;
3238 44 : break;
3239 : }
3240 : }
3241 :
3242 60 : LWLockRelease(ProcArrayLock);
3243 :
3244 60 : return result;
3245 : }
3246 :
3247 : /*
3248 : * IsBackendPid -- is a given pid a running backend
3249 : *
3250 : * This is not called by the backend, but is called by external modules.
3251 : */
3252 : bool
3253 4 : IsBackendPid(int pid)
3254 : {
3255 4 : return (BackendPidGetProc(pid) != NULL);
3256 : }
3257 :
3258 :
3259 : /*
3260 : * GetCurrentVirtualXIDs -- returns an array of currently active VXIDs.
3261 : *
3262 : * The array is palloc'd. The number of valid entries is returned into *nvxids.
3263 : *
3264 : * The arguments allow filtering the set of VXIDs returned. Our own process
3265 : * is always skipped. In addition:
3266 : * If limitXmin is not InvalidTransactionId, skip processes with
3267 : * xmin > limitXmin.
3268 : * If excludeXmin0 is true, skip processes with xmin = 0.
3269 : * If allDbs is false, skip processes attached to other databases.
3270 : * If excludeVacuum isn't zero, skip processes for which
3271 : * (statusFlags & excludeVacuum) is not zero.
3272 : *
3273 : * Note: the purpose of the limitXmin and excludeXmin0 parameters is to
3274 : * allow skipping backends whose oldest live snapshot is no older than
3275 : * some snapshot we have. Since we examine the procarray with only shared
3276 : * lock, there are race conditions: a backend could set its xmin just after
3277 : * we look. Indeed, on multiprocessors with weak memory ordering, the
3278 : * other backend could have set its xmin *before* we look. We know however
3279 : * that such a backend must have held shared ProcArrayLock overlapping our
3280 : * own hold of ProcArrayLock, else we would see its xmin update. Therefore,
3281 : * any snapshot the other backend is taking concurrently with our scan cannot
3282 : * consider any transactions as still running that we think are committed
3283 : * (since backends must hold ProcArrayLock exclusive to commit).
3284 : */
3285 : VirtualTransactionId *
3286 752 : GetCurrentVirtualXIDs(TransactionId limitXmin, bool excludeXmin0,
3287 : bool allDbs, int excludeVacuum,
3288 : int *nvxids)
3289 : {
3290 : VirtualTransactionId *vxids;
3291 752 : ProcArrayStruct *arrayP = procArray;
3292 752 : int count = 0;
3293 : int index;
3294 :
3295 : /* allocate what's certainly enough result space */
3296 : vxids = (VirtualTransactionId *)
3297 752 : palloc(sizeof(VirtualTransactionId) * arrayP->maxProcs);
3298 :
3299 752 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3300 :
3301 4428 : for (index = 0; index < arrayP->numProcs; index++)
3302 : {
3303 3676 : int pgprocno = arrayP->pgprocnos[index];
3304 3676 : PGPROC *proc = &allProcs[pgprocno];
3305 3676 : uint8 statusFlags = ProcGlobal->statusFlags[index];
3306 :
3307 3676 : if (proc == MyProc)
3308 752 : continue;
3309 :
3310 2924 : if (excludeVacuum & statusFlags)
3311 12 : continue;
3312 :
3313 2912 : if (allDbs || proc->databaseId == MyDatabaseId)
3314 : {
3315 : /* Fetch xmin just once - might change on us */
3316 1256 : TransactionId pxmin = UINT32_ACCESS_ONCE(proc->xmin);
3317 :
3318 1256 : if (excludeXmin0 && !TransactionIdIsValid(pxmin))
3319 772 : continue;
3320 :
3321 : /*
3322 : * InvalidTransactionId precedes all other XIDs, so a proc that
3323 : * hasn't set xmin yet will not be rejected by this test.
3324 : */
3325 968 : if (!TransactionIdIsValid(limitXmin) ||
3326 484 : TransactionIdPrecedesOrEquals(pxmin, limitXmin))
3327 : {
3328 : VirtualTransactionId vxid;
3329 :
3330 442 : GET_VXID_FROM_PGPROC(vxid, *proc);
3331 442 : if (VirtualTransactionIdIsValid(vxid))
3332 442 : vxids[count++] = vxid;
3333 : }
3334 : }
3335 : }
3336 :
3337 752 : LWLockRelease(ProcArrayLock);
3338 :
3339 752 : *nvxids = count;
3340 752 : return vxids;
3341 : }
3342 :
3343 : /*
3344 : * GetConflictingVirtualXIDs -- returns an array of currently active VXIDs.
3345 : *
3346 : * Usage is limited to conflict resolution during recovery on standby servers.
3347 : * limitXmin is supplied as either a cutoff with snapshotConflictHorizon
3348 : * semantics, or InvalidTransactionId in cases where caller cannot accurately
3349 : * determine a safe snapshotConflictHorizon value.
3350 : *
3351 : * If limitXmin is InvalidTransactionId then we want to kill everybody,
3352 : * so we're not worried if they have a snapshot or not, nor does it really
3353 : * matter what type of lock we hold. Caller must avoid calling here with
3354 : * snapshotConflictHorizon style cutoffs that were set to InvalidTransactionId
3355 : * during original execution, since that actually indicates that there is
3356 : * definitely no need for a recovery conflict (the snapshotConflictHorizon
3357 : * convention for InvalidTransactionId values is the opposite of our own!).
3358 : *
3359 : * All callers that are checking xmins always now supply a valid and useful
3360 : * value for limitXmin. The limitXmin is always lower than the lowest
3361 : * numbered KnownAssignedXid that is not already a FATAL error. This is
3362 : * because we only care about cleanup records that are cleaning up tuple
3363 : * versions from committed transactions. In that case they will only occur
3364 : * at the point where the record is less than the lowest running xid. That
3365 : * allows us to say that if any backend takes a snapshot concurrently with
3366 : * us then the conflict assessment made here would never include the snapshot
3367 : * that is being derived. So we take LW_SHARED on the ProcArray and allow
3368 : * concurrent snapshots when limitXmin is valid. We might think about adding
3369 : * Assert(limitXmin < lowest(KnownAssignedXids))
3370 : * but that would not be true in the case of FATAL errors lagging in array,
3371 : * but we already know those are bogus anyway, so we skip that test.
3372 : *
3373 : * If dbOid is valid we skip backends attached to other databases.
3374 : *
3375 : * Be careful to *not* pfree the result from this function. We reuse
3376 : * this array sufficiently often that we use malloc for the result.
3377 : */
3378 : VirtualTransactionId *
3379 28022 : GetConflictingVirtualXIDs(TransactionId limitXmin, Oid dbOid)
3380 : {
3381 : static VirtualTransactionId *vxids;
3382 28022 : ProcArrayStruct *arrayP = procArray;
3383 28022 : int count = 0;
3384 : int index;
3385 :
3386 : /*
3387 : * If first time through, get workspace to remember main XIDs in. We
3388 : * malloc it permanently to avoid repeated palloc/pfree overhead. Allow
3389 : * result space, remembering room for a terminator.
3390 : */
3391 28022 : if (vxids == NULL)
3392 : {
3393 54 : vxids = (VirtualTransactionId *)
3394 54 : malloc(sizeof(VirtualTransactionId) * (arrayP->maxProcs + 1));
3395 54 : if (vxids == NULL)
3396 0 : ereport(ERROR,
3397 : (errcode(ERRCODE_OUT_OF_MEMORY),
3398 : errmsg("out of memory")));
3399 : }
3400 :
3401 28022 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3402 :
3403 28316 : for (index = 0; index < arrayP->numProcs; index++)
3404 : {
3405 294 : int pgprocno = arrayP->pgprocnos[index];
3406 294 : PGPROC *proc = &allProcs[pgprocno];
3407 :
3408 : /* Exclude prepared transactions */
3409 294 : if (proc->pid == 0)
3410 0 : continue;
3411 :
3412 294 : if (!OidIsValid(dbOid) ||
3413 280 : proc->databaseId == dbOid)
3414 : {
3415 : /* Fetch xmin just once - can't change on us, but good coding */
3416 36 : TransactionId pxmin = UINT32_ACCESS_ONCE(proc->xmin);
3417 :
3418 : /*
3419 : * We ignore an invalid pxmin because this means that backend has
3420 : * no snapshot currently. We hold a Share lock to avoid contention
3421 : * with users taking snapshots. That is not a problem because the
3422 : * current xmin is always at least one higher than the latest
3423 : * removed xid, so any new snapshot would never conflict with the
3424 : * test here.
3425 : */
3426 36 : if (!TransactionIdIsValid(limitXmin) ||
3427 8 : (TransactionIdIsValid(pxmin) && !TransactionIdFollows(pxmin, limitXmin)))
3428 : {
3429 : VirtualTransactionId vxid;
3430 :
3431 4 : GET_VXID_FROM_PGPROC(vxid, *proc);
3432 4 : if (VirtualTransactionIdIsValid(vxid))
3433 4 : vxids[count++] = vxid;
3434 : }
3435 : }
3436 : }
3437 :
3438 28022 : LWLockRelease(ProcArrayLock);
3439 :
3440 : /* add the terminator */
3441 28022 : vxids[count].procNumber = INVALID_PROC_NUMBER;
3442 28022 : vxids[count].localTransactionId = InvalidLocalTransactionId;
3443 :
3444 28022 : return vxids;
3445 : }
3446 :
3447 : /*
3448 : * CancelVirtualTransaction - used in recovery conflict processing
3449 : *
3450 : * Returns pid of the process signaled, or 0 if not found.
3451 : */
3452 : pid_t
3453 6 : CancelVirtualTransaction(VirtualTransactionId vxid, ProcSignalReason sigmode)
3454 : {
3455 6 : return SignalVirtualTransaction(vxid, sigmode, true);
3456 : }
3457 :
3458 : pid_t
3459 10 : SignalVirtualTransaction(VirtualTransactionId vxid, ProcSignalReason sigmode,
3460 : bool conflictPending)
3461 : {
3462 10 : ProcArrayStruct *arrayP = procArray;
3463 : int index;
3464 10 : pid_t pid = 0;
3465 :
3466 10 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3467 :
3468 10 : for (index = 0; index < arrayP->numProcs; index++)
3469 : {
3470 10 : int pgprocno = arrayP->pgprocnos[index];
3471 10 : PGPROC *proc = &allProcs[pgprocno];
3472 : VirtualTransactionId procvxid;
3473 :
3474 10 : GET_VXID_FROM_PGPROC(procvxid, *proc);
3475 :
3476 10 : if (procvxid.procNumber == vxid.procNumber &&
3477 10 : procvxid.localTransactionId == vxid.localTransactionId)
3478 : {
3479 10 : proc->recoveryConflictPending = conflictPending;
3480 10 : pid = proc->pid;
3481 10 : if (pid != 0)
3482 : {
3483 : /*
3484 : * Kill the pid if it's still here. If not, that's what we
3485 : * wanted so ignore any errors.
3486 : */
3487 10 : (void) SendProcSignal(pid, sigmode, vxid.procNumber);
3488 : }
3489 10 : break;
3490 : }
3491 : }
3492 :
3493 10 : LWLockRelease(ProcArrayLock);
3494 :
3495 10 : return pid;
3496 : }
3497 :
3498 : /*
3499 : * MinimumActiveBackends --- count backends (other than myself) that are
3500 : * in active transactions. Return true if the count exceeds the
3501 : * minimum threshold passed. This is used as a heuristic to decide if
3502 : * a pre-XLOG-flush delay is worthwhile during commit.
3503 : *
3504 : * Do not count backends that are blocked waiting for locks, since they are
3505 : * not going to get to run until someone else commits.
3506 : */
3507 : bool
3508 0 : MinimumActiveBackends(int min)
3509 : {
3510 0 : ProcArrayStruct *arrayP = procArray;
3511 0 : int count = 0;
3512 : int index;
3513 :
3514 : /* Quick short-circuit if no minimum is specified */
3515 0 : if (min == 0)
3516 0 : return true;
3517 :
3518 : /*
3519 : * Note: for speed, we don't acquire ProcArrayLock. This is a little bit
3520 : * bogus, but since we are only testing fields for zero or nonzero, it
3521 : * should be OK. The result is only used for heuristic purposes anyway...
3522 : */
3523 0 : for (index = 0; index < arrayP->numProcs; index++)
3524 : {
3525 0 : int pgprocno = arrayP->pgprocnos[index];
3526 0 : PGPROC *proc = &allProcs[pgprocno];
3527 :
3528 : /*
3529 : * Since we're not holding a lock, need to be prepared to deal with
3530 : * garbage, as someone could have incremented numProcs but not yet
3531 : * filled the structure.
3532 : *
3533 : * If someone just decremented numProcs, 'proc' could also point to a
3534 : * PGPROC entry that's no longer in the array. It still points to a
3535 : * PGPROC struct, though, because freed PGPROC entries just go to the
3536 : * free list and are recycled. Its contents are nonsense in that case,
3537 : * but that's acceptable for this function.
3538 : */
3539 0 : if (pgprocno == -1)
3540 0 : continue; /* do not count deleted entries */
3541 0 : if (proc == MyProc)
3542 0 : continue; /* do not count myself */
3543 0 : if (proc->xid == InvalidTransactionId)
3544 0 : continue; /* do not count if no XID assigned */
3545 0 : if (proc->pid == 0)
3546 0 : continue; /* do not count prepared xacts */
3547 0 : if (proc->waitLock != NULL)
3548 0 : continue; /* do not count if blocked on a lock */
3549 0 : count++;
3550 0 : if (count >= min)
3551 0 : break;
3552 : }
3553 :
3554 0 : return count >= min;
3555 : }
3556 :
3557 : /*
3558 : * CountDBBackends --- count backends that are using specified database
3559 : */
3560 : int
3561 30 : CountDBBackends(Oid databaseid)
3562 : {
3563 30 : ProcArrayStruct *arrayP = procArray;
3564 30 : int count = 0;
3565 : int index;
3566 :
3567 30 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3568 :
3569 44 : for (index = 0; index < arrayP->numProcs; index++)
3570 : {
3571 14 : int pgprocno = arrayP->pgprocnos[index];
3572 14 : PGPROC *proc = &allProcs[pgprocno];
3573 :
3574 14 : if (proc->pid == 0)
3575 0 : continue; /* do not count prepared xacts */
3576 14 : if (!OidIsValid(databaseid) ||
3577 14 : proc->databaseId == databaseid)
3578 4 : count++;
3579 : }
3580 :
3581 30 : LWLockRelease(ProcArrayLock);
3582 :
3583 30 : return count;
3584 : }
3585 :
3586 : /*
3587 : * CountDBConnections --- counts database backends (only regular backends)
3588 : */
3589 : int
3590 0 : CountDBConnections(Oid databaseid)
3591 : {
3592 0 : ProcArrayStruct *arrayP = procArray;
3593 0 : int count = 0;
3594 : int index;
3595 :
3596 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3597 :
3598 0 : for (index = 0; index < arrayP->numProcs; index++)
3599 : {
3600 0 : int pgprocno = arrayP->pgprocnos[index];
3601 0 : PGPROC *proc = &allProcs[pgprocno];
3602 :
3603 0 : if (proc->pid == 0)
3604 0 : continue; /* do not count prepared xacts */
3605 0 : if (!proc->isRegularBackend)
3606 0 : continue; /* count only regular backend processes */
3607 0 : if (!OidIsValid(databaseid) ||
3608 0 : proc->databaseId == databaseid)
3609 0 : count++;
3610 : }
3611 :
3612 0 : LWLockRelease(ProcArrayLock);
3613 :
3614 0 : return count;
3615 : }
3616 :
3617 : /*
3618 : * CancelDBBackends --- cancel backends that are using specified database
3619 : */
3620 : void
3621 18 : CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conflictPending)
3622 : {
3623 18 : ProcArrayStruct *arrayP = procArray;
3624 : int index;
3625 :
3626 : /* tell all backends to die */
3627 18 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
3628 :
3629 36 : for (index = 0; index < arrayP->numProcs; index++)
3630 : {
3631 18 : int pgprocno = arrayP->pgprocnos[index];
3632 18 : PGPROC *proc = &allProcs[pgprocno];
3633 :
3634 18 : if (databaseid == InvalidOid || proc->databaseId == databaseid)
3635 : {
3636 : VirtualTransactionId procvxid;
3637 : pid_t pid;
3638 :
3639 18 : GET_VXID_FROM_PGPROC(procvxid, *proc);
3640 :
3641 18 : proc->recoveryConflictPending = conflictPending;
3642 18 : pid = proc->pid;
3643 18 : if (pid != 0)
3644 : {
3645 : /*
3646 : * Kill the pid if it's still here. If not, that's what we
3647 : * wanted so ignore any errors.
3648 : */
3649 18 : (void) SendProcSignal(pid, sigmode, procvxid.procNumber);
3650 : }
3651 : }
3652 : }
3653 :
3654 18 : LWLockRelease(ProcArrayLock);
3655 18 : }
3656 :
3657 : /*
3658 : * CountUserBackends --- count backends that are used by specified user
3659 : * (only regular backends, not any type of background worker)
3660 : */
3661 : int
3662 0 : CountUserBackends(Oid roleid)
3663 : {
3664 0 : ProcArrayStruct *arrayP = procArray;
3665 0 : int count = 0;
3666 : int index;
3667 :
3668 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3669 :
3670 0 : for (index = 0; index < arrayP->numProcs; index++)
3671 : {
3672 0 : int pgprocno = arrayP->pgprocnos[index];
3673 0 : PGPROC *proc = &allProcs[pgprocno];
3674 :
3675 0 : if (proc->pid == 0)
3676 0 : continue; /* do not count prepared xacts */
3677 0 : if (!proc->isRegularBackend)
3678 0 : continue; /* count only regular backend processes */
3679 0 : if (proc->roleId == roleid)
3680 0 : count++;
3681 : }
3682 :
3683 0 : LWLockRelease(ProcArrayLock);
3684 :
3685 0 : return count;
3686 : }
3687 :
3688 : /*
3689 : * CountOtherDBBackends -- check for other backends running in the given DB
3690 : *
3691 : * If there are other backends in the DB, we will wait a maximum of 5 seconds
3692 : * for them to exit. Autovacuum backends are encouraged to exit early by
3693 : * sending them SIGTERM, but normal user backends are just waited for.
3694 : *
3695 : * The current backend is always ignored; it is caller's responsibility to
3696 : * check whether the current backend uses the given DB, if it's important.
3697 : *
3698 : * Returns true if there are (still) other backends in the DB, false if not.
3699 : * Also, *nbackends and *nprepared are set to the number of other backends
3700 : * and prepared transactions in the DB, respectively.
3701 : *
3702 : * This function is used to interlock DROP DATABASE and related commands
3703 : * against there being any active backends in the target DB --- dropping the
3704 : * DB while active backends remain would be a Bad Thing. Note that we cannot
3705 : * detect here the possibility of a newly-started backend that is trying to
3706 : * connect to the doomed database, so additional interlocking is needed during
3707 : * backend startup. The caller should normally hold an exclusive lock on the
3708 : * target DB before calling this, which is one reason we mustn't wait
3709 : * indefinitely.
3710 : */
3711 : bool
3712 866 : CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
3713 : {
3714 866 : ProcArrayStruct *arrayP = procArray;
3715 :
3716 : #define MAXAUTOVACPIDS 10 /* max autovacs to SIGTERM per iteration */
3717 : int autovac_pids[MAXAUTOVACPIDS];
3718 : int tries;
3719 :
3720 : /* 50 tries with 100ms sleep between tries makes 5 sec total wait */
3721 866 : for (tries = 0; tries < 50; tries++)
3722 : {
3723 866 : int nautovacs = 0;
3724 866 : bool found = false;
3725 : int index;
3726 :
3727 866 : CHECK_FOR_INTERRUPTS();
3728 :
3729 866 : *nbackends = *nprepared = 0;
3730 :
3731 866 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3732 :
3733 3166 : for (index = 0; index < arrayP->numProcs; index++)
3734 : {
3735 2300 : int pgprocno = arrayP->pgprocnos[index];
3736 2300 : PGPROC *proc = &allProcs[pgprocno];
3737 2300 : uint8 statusFlags = ProcGlobal->statusFlags[index];
3738 :
3739 2300 : if (proc->databaseId != databaseId)
3740 2104 : continue;
3741 196 : if (proc == MyProc)
3742 196 : continue;
3743 :
3744 0 : found = true;
3745 :
3746 0 : if (proc->pid == 0)
3747 0 : (*nprepared)++;
3748 : else
3749 : {
3750 0 : (*nbackends)++;
3751 0 : if ((statusFlags & PROC_IS_AUTOVACUUM) &&
3752 : nautovacs < MAXAUTOVACPIDS)
3753 0 : autovac_pids[nautovacs++] = proc->pid;
3754 : }
3755 : }
3756 :
3757 866 : LWLockRelease(ProcArrayLock);
3758 :
3759 866 : if (!found)
3760 866 : return false; /* no conflicting backends, so done */
3761 :
3762 : /*
3763 : * Send SIGTERM to any conflicting autovacuums before sleeping. We
3764 : * postpone this step until after the loop because we don't want to
3765 : * hold ProcArrayLock while issuing kill(). We have no idea what might
3766 : * block kill() inside the kernel...
3767 : */
3768 0 : for (index = 0; index < nautovacs; index++)
3769 0 : (void) kill(autovac_pids[index], SIGTERM); /* ignore any error */
3770 :
3771 : /* sleep, then try again */
3772 0 : pg_usleep(100 * 1000L); /* 100ms */
3773 : }
3774 :
3775 0 : return true; /* timed out, still conflicts */
3776 : }
3777 :
3778 : /*
3779 : * Terminate existing connections to the specified database. This routine
3780 : * is used by the DROP DATABASE command when user has asked to forcefully
3781 : * drop the database.
3782 : *
3783 : * The current backend is always ignored; it is caller's responsibility to
3784 : * check whether the current backend uses the given DB, if it's important.
3785 : *
3786 : * If the target database has a prepared transaction or permissions checks
3787 : * fail for a connection, this fails without terminating anything.
3788 : */
3789 : void
3790 2 : TerminateOtherDBBackends(Oid databaseId)
3791 : {
3792 2 : ProcArrayStruct *arrayP = procArray;
3793 2 : List *pids = NIL;
3794 2 : int nprepared = 0;
3795 : int i;
3796 :
3797 2 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3798 :
3799 8 : for (i = 0; i < procArray->numProcs; i++)
3800 : {
3801 6 : int pgprocno = arrayP->pgprocnos[i];
3802 6 : PGPROC *proc = &allProcs[pgprocno];
3803 :
3804 6 : if (proc->databaseId != databaseId)
3805 6 : continue;
3806 0 : if (proc == MyProc)
3807 0 : continue;
3808 :
3809 0 : if (proc->pid != 0)
3810 0 : pids = lappend_int(pids, proc->pid);
3811 : else
3812 0 : nprepared++;
3813 : }
3814 :
3815 2 : LWLockRelease(ProcArrayLock);
3816 :
3817 2 : if (nprepared > 0)
3818 0 : ereport(ERROR,
3819 : (errcode(ERRCODE_OBJECT_IN_USE),
3820 : errmsg("database \"%s\" is being used by prepared transactions",
3821 : get_database_name(databaseId)),
3822 : errdetail_plural("There is %d prepared transaction using the database.",
3823 : "There are %d prepared transactions using the database.",
3824 : nprepared,
3825 : nprepared)));
3826 :
3827 2 : if (pids)
3828 : {
3829 : ListCell *lc;
3830 :
3831 : /*
3832 : * Permissions checks relax the pg_terminate_backend checks in two
3833 : * ways, both by omitting the !OidIsValid(proc->roleId) check:
3834 : *
3835 : * - Accept terminating autovacuum workers, since DROP DATABASE
3836 : * without FORCE terminates them.
3837 : *
3838 : * - Accept terminating bgworkers. For bgworker authors, it's
3839 : * convenient to be able to recommend FORCE if a worker is blocking
3840 : * DROP DATABASE unexpectedly.
3841 : *
3842 : * Unlike pg_terminate_backend, we don't raise some warnings - like
3843 : * "PID %d is not a PostgreSQL server process", because for us already
3844 : * finished session is not a problem.
3845 : */
3846 0 : foreach(lc, pids)
3847 : {
3848 0 : int pid = lfirst_int(lc);
3849 0 : PGPROC *proc = BackendPidGetProc(pid);
3850 :
3851 0 : if (proc != NULL)
3852 : {
3853 0 : if (superuser_arg(proc->roleId) && !superuser())
3854 0 : ereport(ERROR,
3855 : (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
3856 : errmsg("permission denied to terminate process"),
3857 : errdetail("Only roles with the %s attribute may terminate processes of roles with the %s attribute.",
3858 : "SUPERUSER", "SUPERUSER")));
3859 :
3860 0 : if (!has_privs_of_role(GetUserId(), proc->roleId) &&
3861 0 : !has_privs_of_role(GetUserId(), ROLE_PG_SIGNAL_BACKEND))
3862 0 : ereport(ERROR,
3863 : (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
3864 : errmsg("permission denied to terminate process"),
3865 : errdetail("Only roles with privileges of the role whose process is being terminated or with privileges of the \"%s\" role may terminate this process.",
3866 : "pg_signal_backend")));
3867 : }
3868 : }
3869 :
3870 : /*
3871 : * There's a race condition here: once we release the ProcArrayLock,
3872 : * it's possible for the session to exit before we issue kill. That
3873 : * race condition possibility seems too unlikely to worry about. See
3874 : * pg_signal_backend.
3875 : */
3876 0 : foreach(lc, pids)
3877 : {
3878 0 : int pid = lfirst_int(lc);
3879 0 : PGPROC *proc = BackendPidGetProc(pid);
3880 :
3881 0 : if (proc != NULL)
3882 : {
3883 : /*
3884 : * If we have setsid(), signal the backend's whole process
3885 : * group
3886 : */
3887 : #ifdef HAVE_SETSID
3888 0 : (void) kill(-pid, SIGTERM);
3889 : #else
3890 : (void) kill(pid, SIGTERM);
3891 : #endif
3892 : }
3893 : }
3894 : }
3895 2 : }
3896 :
3897 : /*
3898 : * ProcArraySetReplicationSlotXmin
3899 : *
3900 : * Install limits to future computations of the xmin horizon to prevent vacuum
3901 : * and HOT pruning from removing affected rows still needed by clients with
3902 : * replication slots.
3903 : */
3904 : void
3905 4588 : ProcArraySetReplicationSlotXmin(TransactionId xmin, TransactionId catalog_xmin,
3906 : bool already_locked)
3907 : {
3908 : Assert(!already_locked || LWLockHeldByMe(ProcArrayLock));
3909 :
3910 4588 : if (!already_locked)
3911 3664 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
3912 :
3913 4588 : procArray->replication_slot_xmin = xmin;
3914 4588 : procArray->replication_slot_catalog_xmin = catalog_xmin;
3915 :
3916 4588 : if (!already_locked)
3917 3664 : LWLockRelease(ProcArrayLock);
3918 :
3919 4588 : elog(DEBUG1, "xmin required by slots: data %u, catalog %u",
3920 : xmin, catalog_xmin);
3921 4588 : }
3922 :
3923 : /*
3924 : * ProcArrayGetReplicationSlotXmin
3925 : *
3926 : * Return the current slot xmin limits. That's useful to be able to remove
3927 : * data that's older than those limits.
3928 : */
3929 : void
3930 44 : ProcArrayGetReplicationSlotXmin(TransactionId *xmin,
3931 : TransactionId *catalog_xmin)
3932 : {
3933 44 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3934 :
3935 44 : if (xmin != NULL)
3936 0 : *xmin = procArray->replication_slot_xmin;
3937 :
3938 44 : if (catalog_xmin != NULL)
3939 44 : *catalog_xmin = procArray->replication_slot_catalog_xmin;
3940 :
3941 44 : LWLockRelease(ProcArrayLock);
3942 44 : }
3943 :
3944 : /*
3945 : * XidCacheRemoveRunningXids
3946 : *
3947 : * Remove a bunch of TransactionIds from the list of known-running
3948 : * subtransactions for my backend. Both the specified xid and those in
3949 : * the xids[] array (of length nxids) are removed from the subxids cache.
3950 : * latestXid must be the latest XID among the group.
3951 : */
3952 : void
3953 1298 : XidCacheRemoveRunningXids(TransactionId xid,
3954 : int nxids, const TransactionId *xids,
3955 : TransactionId latestXid)
3956 : {
3957 : int i,
3958 : j;
3959 : XidCacheStatus *mysubxidstat;
3960 :
3961 : Assert(TransactionIdIsValid(xid));
3962 :
3963 : /*
3964 : * We must hold ProcArrayLock exclusively in order to remove transactions
3965 : * from the PGPROC array. (See src/backend/access/transam/README.) It's
3966 : * possible this could be relaxed since we know this routine is only used
3967 : * to abort subtransactions, but pending closer analysis we'd best be
3968 : * conservative.
3969 : *
3970 : * Note that we do not have to be careful about memory ordering of our own
3971 : * reads wrt. GetNewTransactionId() here - only this process can modify
3972 : * relevant fields of MyProc/ProcGlobal->xids[]. But we do have to be
3973 : * careful about our own writes being well ordered.
3974 : */
3975 1298 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
3976 :
3977 1298 : mysubxidstat = &ProcGlobal->subxidStates[MyProc->pgxactoff];
3978 :
3979 : /*
3980 : * Under normal circumstances xid and xids[] will be in increasing order,
3981 : * as will be the entries in subxids. Scan backwards to avoid O(N^2)
3982 : * behavior when removing a lot of xids.
3983 : */
3984 1358 : for (i = nxids - 1; i >= 0; i--)
3985 : {
3986 60 : TransactionId anxid = xids[i];
3987 :
3988 60 : for (j = MyProc->subxidStatus.count - 1; j >= 0; j--)
3989 : {
3990 60 : if (TransactionIdEquals(MyProc->subxids.xids[j], anxid))
3991 : {
3992 60 : MyProc->subxids.xids[j] = MyProc->subxids.xids[MyProc->subxidStatus.count - 1];
3993 60 : pg_write_barrier();
3994 60 : mysubxidstat->count--;
3995 60 : MyProc->subxidStatus.count--;
3996 60 : break;
3997 : }
3998 : }
3999 :
4000 : /*
4001 : * Ordinarily we should have found it, unless the cache has
4002 : * overflowed. However it's also possible for this routine to be
4003 : * invoked multiple times for the same subtransaction, in case of an
4004 : * error during AbortSubTransaction. So instead of Assert, emit a
4005 : * debug warning.
4006 : */
4007 60 : if (j < 0 && !MyProc->subxidStatus.overflowed)
4008 0 : elog(WARNING, "did not find subXID %u in MyProc", anxid);
4009 : }
4010 :
4011 1426 : for (j = MyProc->subxidStatus.count - 1; j >= 0; j--)
4012 : {
4013 1424 : if (TransactionIdEquals(MyProc->subxids.xids[j], xid))
4014 : {
4015 1296 : MyProc->subxids.xids[j] = MyProc->subxids.xids[MyProc->subxidStatus.count - 1];
4016 1296 : pg_write_barrier();
4017 1296 : mysubxidstat->count--;
4018 1296 : MyProc->subxidStatus.count--;
4019 1296 : break;
4020 : }
4021 : }
4022 : /* Ordinarily we should have found it, unless the cache has overflowed */
4023 1298 : if (j < 0 && !MyProc->subxidStatus.overflowed)
4024 0 : elog(WARNING, "did not find subXID %u in MyProc", xid);
4025 :
4026 : /* Also advance global latestCompletedXid while holding the lock */
4027 1298 : MaintainLatestCompletedXid(latestXid);
4028 :
4029 : /* ... and xactCompletionCount */
4030 1298 : TransamVariables->xactCompletionCount++;
4031 :
4032 1298 : LWLockRelease(ProcArrayLock);
4033 1298 : }
4034 :
4035 : #ifdef XIDCACHE_DEBUG
4036 :
4037 : /*
4038 : * Print stats about effectiveness of XID cache
4039 : */
4040 : static void
4041 : DisplayXidCache(void)
4042 : {
4043 : fprintf(stderr,
4044 : "XidCache: xmin: %ld, known: %ld, myxact: %ld, latest: %ld, mainxid: %ld, childxid: %ld, knownassigned: %ld, nooflo: %ld, slow: %ld\n",
4045 : xc_by_recent_xmin,
4046 : xc_by_known_xact,
4047 : xc_by_my_xact,
4048 : xc_by_latest_xid,
4049 : xc_by_main_xid,
4050 : xc_by_child_xid,
4051 : xc_by_known_assigned,
4052 : xc_no_overflow,
4053 : xc_slow_answer);
4054 : }
4055 : #endif /* XIDCACHE_DEBUG */
4056 :
4057 : /*
4058 : * If rel != NULL, return test state appropriate for relation, otherwise
4059 : * return state usable for all relations. The latter may consider XIDs as
4060 : * not-yet-visible-to-everyone that a state for a specific relation would
4061 : * already consider visible-to-everyone.
4062 : *
4063 : * This needs to be called while a snapshot is active or registered, otherwise
4064 : * there are wraparound and other dangers.
4065 : *
4066 : * See comment for GlobalVisState for details.
4067 : */
4068 : GlobalVisState *
4069 28569152 : GlobalVisTestFor(Relation rel)
4070 : {
4071 28569152 : GlobalVisState *state = NULL;
4072 :
4073 : /* XXX: we should assert that a snapshot is pushed or registered */
4074 : Assert(RecentXmin);
4075 :
4076 28569152 : switch (GlobalVisHorizonKindForRel(rel))
4077 : {
4078 176236 : case VISHORIZON_SHARED:
4079 176236 : state = &GlobalVisSharedRels;
4080 176236 : break;
4081 5708342 : case VISHORIZON_CATALOG:
4082 5708342 : state = &GlobalVisCatalogRels;
4083 5708342 : break;
4084 22600686 : case VISHORIZON_DATA:
4085 22600686 : state = &GlobalVisDataRels;
4086 22600686 : break;
4087 83888 : case VISHORIZON_TEMP:
4088 83888 : state = &GlobalVisTempRels;
4089 83888 : break;
4090 : }
4091 :
4092 : Assert(FullTransactionIdIsValid(state->definitely_needed) &&
4093 : FullTransactionIdIsValid(state->maybe_needed));
4094 :
4095 28569152 : return state;
4096 : }
4097 :
4098 : /*
4099 : * Return true if it's worth updating the accurate maybe_needed boundary.
4100 : *
4101 : * As it is somewhat expensive to determine xmin horizons, we don't want to
4102 : * repeatedly do so when there is a low likelihood of it being beneficial.
4103 : *
4104 : * The current heuristic is that we update only if RecentXmin has changed
4105 : * since the last update. If the oldest currently running transaction has not
4106 : * finished, it is unlikely that recomputing the horizon would be useful.
4107 : */
4108 : static bool
4109 821246 : GlobalVisTestShouldUpdate(GlobalVisState *state)
4110 : {
4111 : /* hasn't been updated yet */
4112 821246 : if (!TransactionIdIsValid(ComputeXidHorizonsResultLastXmin))
4113 16958 : return true;
4114 :
4115 : /*
4116 : * If the maybe_needed/definitely_needed boundaries are the same, it's
4117 : * unlikely to be beneficial to refresh boundaries.
4118 : */
4119 804288 : if (FullTransactionIdFollowsOrEquals(state->maybe_needed,
4120 : state->definitely_needed))
4121 0 : return false;
4122 :
4123 : /* does the last snapshot built have a different xmin? */
4124 804288 : return RecentXmin != ComputeXidHorizonsResultLastXmin;
4125 : }
4126 :
4127 : static void
4128 420090 : GlobalVisUpdateApply(ComputeXidHorizonsResult *horizons)
4129 : {
4130 : GlobalVisSharedRels.maybe_needed =
4131 420090 : FullXidRelativeTo(horizons->latest_completed,
4132 : horizons->shared_oldest_nonremovable);
4133 : GlobalVisCatalogRels.maybe_needed =
4134 420090 : FullXidRelativeTo(horizons->latest_completed,
4135 : horizons->catalog_oldest_nonremovable);
4136 : GlobalVisDataRels.maybe_needed =
4137 420090 : FullXidRelativeTo(horizons->latest_completed,
4138 : horizons->data_oldest_nonremovable);
4139 : GlobalVisTempRels.maybe_needed =
4140 420090 : FullXidRelativeTo(horizons->latest_completed,
4141 : horizons->temp_oldest_nonremovable);
4142 :
4143 : /*
4144 : * In longer running transactions it's possible that transactions we
4145 : * previously needed to treat as running aren't around anymore. So update
4146 : * definitely_needed to not be earlier than maybe_needed.
4147 : */
4148 : GlobalVisSharedRels.definitely_needed =
4149 420090 : FullTransactionIdNewer(GlobalVisSharedRels.maybe_needed,
4150 : GlobalVisSharedRels.definitely_needed);
4151 : GlobalVisCatalogRels.definitely_needed =
4152 420090 : FullTransactionIdNewer(GlobalVisCatalogRels.maybe_needed,
4153 : GlobalVisCatalogRels.definitely_needed);
4154 : GlobalVisDataRels.definitely_needed =
4155 420090 : FullTransactionIdNewer(GlobalVisDataRels.maybe_needed,
4156 : GlobalVisDataRels.definitely_needed);
4157 420090 : GlobalVisTempRels.definitely_needed = GlobalVisTempRels.maybe_needed;
4158 :
4159 420090 : ComputeXidHorizonsResultLastXmin = RecentXmin;
4160 420090 : }
4161 :
4162 : /*
4163 : * Update boundaries in GlobalVis{Shared,Catalog, Data}Rels
4164 : * using ComputeXidHorizons().
4165 : */
4166 : static void
4167 110496 : GlobalVisUpdate(void)
4168 : {
4169 : ComputeXidHorizonsResult horizons;
4170 :
4171 : /* updates the horizons as a side-effect */
4172 110496 : ComputeXidHorizons(&horizons);
4173 110496 : }
4174 :
4175 : /*
4176 : * Return true if no snapshot still considers fxid to be running.
4177 : *
4178 : * The state passed needs to have been initialized for the relation fxid is
4179 : * from (NULL is also OK), otherwise the result may not be correct.
4180 : *
4181 : * See comment for GlobalVisState for details.
4182 : */
4183 : bool
4184 19080788 : GlobalVisTestIsRemovableFullXid(GlobalVisState *state,
4185 : FullTransactionId fxid)
4186 : {
4187 : /*
4188 : * If fxid is older than maybe_needed bound, it definitely is visible to
4189 : * everyone.
4190 : */
4191 19080788 : if (FullTransactionIdPrecedes(fxid, state->maybe_needed))
4192 4840712 : return true;
4193 :
4194 : /*
4195 : * If fxid is >= definitely_needed bound, it is very likely to still be
4196 : * considered running.
4197 : */
4198 14240076 : if (FullTransactionIdFollowsOrEquals(fxid, state->definitely_needed))
4199 13418830 : return false;
4200 :
4201 : /*
4202 : * fxid is between maybe_needed and definitely_needed, i.e. there might or
4203 : * might not exist a snapshot considering fxid running. If it makes sense,
4204 : * update boundaries and recheck.
4205 : */
4206 821246 : if (GlobalVisTestShouldUpdate(state))
4207 : {
4208 110496 : GlobalVisUpdate();
4209 :
4210 : Assert(FullTransactionIdPrecedes(fxid, state->definitely_needed));
4211 :
4212 110496 : return FullTransactionIdPrecedes(fxid, state->maybe_needed);
4213 : }
4214 : else
4215 710750 : return false;
4216 : }
4217 :
4218 : /*
4219 : * Wrapper around GlobalVisTestIsRemovableFullXid() for 32bit xids.
4220 : *
4221 : * It is crucial that this only gets called for xids from a source that
4222 : * protects against xid wraparounds (e.g. from a table and thus protected by
4223 : * relfrozenxid).
4224 : */
4225 : bool
4226 19080026 : GlobalVisTestIsRemovableXid(GlobalVisState *state, TransactionId xid)
4227 : {
4228 : FullTransactionId fxid;
4229 :
4230 : /*
4231 : * Convert 32 bit argument to FullTransactionId. We can do so safely
4232 : * because we know the xid has to, at the very least, be between
4233 : * [oldestXid, nextXid), i.e. within 2 billion of xid. To avoid taking a
4234 : * lock to determine either, we can just compare with
4235 : * state->definitely_needed, which was based on those value at the time
4236 : * the current snapshot was built.
4237 : */
4238 19080026 : fxid = FullXidRelativeTo(state->definitely_needed, xid);
4239 :
4240 19080026 : return GlobalVisTestIsRemovableFullXid(state, fxid);
4241 : }
4242 :
4243 : /*
4244 : * Convenience wrapper around GlobalVisTestFor() and
4245 : * GlobalVisTestIsRemovableFullXid(), see their comments.
4246 : */
4247 : bool
4248 762 : GlobalVisCheckRemovableFullXid(Relation rel, FullTransactionId fxid)
4249 : {
4250 : GlobalVisState *state;
4251 :
4252 762 : state = GlobalVisTestFor(rel);
4253 :
4254 762 : return GlobalVisTestIsRemovableFullXid(state, fxid);
4255 : }
4256 :
4257 : /*
4258 : * Convenience wrapper around GlobalVisTestFor() and
4259 : * GlobalVisTestIsRemovableXid(), see their comments.
4260 : */
4261 : bool
4262 12 : GlobalVisCheckRemovableXid(Relation rel, TransactionId xid)
4263 : {
4264 : GlobalVisState *state;
4265 :
4266 12 : state = GlobalVisTestFor(rel);
4267 :
4268 12 : return GlobalVisTestIsRemovableXid(state, xid);
4269 : }
4270 :
4271 : /*
4272 : * Convert a 32 bit transaction id into 64 bit transaction id, by assuming it
4273 : * is within MaxTransactionId / 2 of XidFromFullTransactionId(rel).
4274 : *
4275 : * Be very careful about when to use this function. It can only safely be used
4276 : * when there is a guarantee that xid is within MaxTransactionId / 2 xids of
4277 : * rel. That e.g. can be guaranteed if the caller assures a snapshot is
4278 : * held by the backend and xid is from a table (where vacuum/freezing ensures
4279 : * the xid has to be within that range), or if xid is from the procarray and
4280 : * prevents xid wraparound that way.
4281 : */
4282 : static inline FullTransactionId
4283 23424148 : FullXidRelativeTo(FullTransactionId rel, TransactionId xid)
4284 : {
4285 23424148 : TransactionId rel_xid = XidFromFullTransactionId(rel);
4286 :
4287 : Assert(TransactionIdIsValid(xid));
4288 : Assert(TransactionIdIsValid(rel_xid));
4289 :
4290 : /* not guaranteed to find issues, but likely to catch mistakes */
4291 : AssertTransactionIdInAllowableRange(xid);
4292 :
4293 46848296 : return FullTransactionIdFromU64(U64FromFullTransactionId(rel)
4294 23424148 : + (int32) (xid - rel_xid));
4295 : }
4296 :
4297 :
4298 : /* ----------------------------------------------
4299 : * KnownAssignedTransactionIds sub-module
4300 : * ----------------------------------------------
4301 : */
4302 :
4303 : /*
4304 : * In Hot Standby mode, we maintain a list of transactions that are (or were)
4305 : * running on the primary at the current point in WAL. These XIDs must be
4306 : * treated as running by standby transactions, even though they are not in
4307 : * the standby server's PGPROC array.
4308 : *
4309 : * We record all XIDs that we know have been assigned. That includes all the
4310 : * XIDs seen in WAL records, plus all unobserved XIDs that we can deduce have
4311 : * been assigned. We can deduce the existence of unobserved XIDs because we
4312 : * know XIDs are assigned in sequence, with no gaps. The KnownAssignedXids
4313 : * list expands as new XIDs are observed or inferred, and contracts when
4314 : * transaction completion records arrive.
4315 : *
4316 : * During hot standby we do not fret too much about the distinction between
4317 : * top-level XIDs and subtransaction XIDs. We store both together in the
4318 : * KnownAssignedXids list. In backends, this is copied into snapshots in
4319 : * GetSnapshotData(), taking advantage of the fact that XidInMVCCSnapshot()
4320 : * doesn't care about the distinction either. Subtransaction XIDs are
4321 : * effectively treated as top-level XIDs and in the typical case pg_subtrans
4322 : * links are *not* maintained (which does not affect visibility).
4323 : *
4324 : * We have room in KnownAssignedXids and in snapshots to hold maxProcs *
4325 : * (1 + PGPROC_MAX_CACHED_SUBXIDS) XIDs, so every primary transaction must
4326 : * report its subtransaction XIDs in a WAL XLOG_XACT_ASSIGNMENT record at
4327 : * least every PGPROC_MAX_CACHED_SUBXIDS. When we receive one of these
4328 : * records, we mark the subXIDs as children of the top XID in pg_subtrans,
4329 : * and then remove them from KnownAssignedXids. This prevents overflow of
4330 : * KnownAssignedXids and snapshots, at the cost that status checks for these
4331 : * subXIDs will take a slower path through TransactionIdIsInProgress().
4332 : * This means that KnownAssignedXids is not necessarily complete for subXIDs,
4333 : * though it should be complete for top-level XIDs; this is the same situation
4334 : * that holds with respect to the PGPROC entries in normal running.
4335 : *
4336 : * When we throw away subXIDs from KnownAssignedXids, we need to keep track of
4337 : * that, similarly to tracking overflow of a PGPROC's subxids array. We do
4338 : * that by remembering the lastOverflowedXid, ie the last thrown-away subXID.
4339 : * As long as that is within the range of interesting XIDs, we have to assume
4340 : * that subXIDs are missing from snapshots. (Note that subXID overflow occurs
4341 : * on primary when 65th subXID arrives, whereas on standby it occurs when 64th
4342 : * subXID arrives - that is not an error.)
4343 : *
4344 : * Should a backend on primary somehow disappear before it can write an abort
4345 : * record, then we just leave those XIDs in KnownAssignedXids. They actually
4346 : * aborted but we think they were running; the distinction is irrelevant
4347 : * because either way any changes done by the transaction are not visible to
4348 : * backends in the standby. We prune KnownAssignedXids when
4349 : * XLOG_RUNNING_XACTS arrives, to forestall possible overflow of the
4350 : * array due to such dead XIDs.
4351 : */
4352 :
4353 : /*
4354 : * RecordKnownAssignedTransactionIds
4355 : * Record the given XID in KnownAssignedXids, as well as any preceding
4356 : * unobserved XIDs.
4357 : *
4358 : * RecordKnownAssignedTransactionIds() should be run for *every* WAL record
4359 : * associated with a transaction. Must be called for each record after we
4360 : * have executed StartupCLOG() et al, since we must ExtendCLOG() etc..
4361 : *
4362 : * Called during recovery in analogy with and in place of GetNewTransactionId()
4363 : */
4364 : void
4365 4922904 : RecordKnownAssignedTransactionIds(TransactionId xid)
4366 : {
4367 : Assert(standbyState >= STANDBY_INITIALIZED);
4368 : Assert(TransactionIdIsValid(xid));
4369 : Assert(TransactionIdIsValid(latestObservedXid));
4370 :
4371 4922904 : elog(DEBUG4, "record known xact %u latestObservedXid %u",
4372 : xid, latestObservedXid);
4373 :
4374 : /*
4375 : * When a newly observed xid arrives, it is frequently the case that it is
4376 : * *not* the next xid in sequence. When this occurs, we must treat the
4377 : * intervening xids as running also.
4378 : */
4379 4922904 : if (TransactionIdFollows(xid, latestObservedXid))
4380 : {
4381 : TransactionId next_expected_xid;
4382 :
4383 : /*
4384 : * Extend subtrans like we do in GetNewTransactionId() during normal
4385 : * operation using individual extend steps. Note that we do not need
4386 : * to extend clog since its extensions are WAL logged.
4387 : *
4388 : * This part has to be done regardless of standbyState since we
4389 : * immediately start assigning subtransactions to their toplevel
4390 : * transactions.
4391 : */
4392 44128 : next_expected_xid = latestObservedXid;
4393 89682 : while (TransactionIdPrecedes(next_expected_xid, xid))
4394 : {
4395 45554 : TransactionIdAdvance(next_expected_xid);
4396 45554 : ExtendSUBTRANS(next_expected_xid);
4397 : }
4398 : Assert(next_expected_xid == xid);
4399 :
4400 : /*
4401 : * If the KnownAssignedXids machinery isn't up yet, there's nothing
4402 : * more to do since we don't track assigned xids yet.
4403 : */
4404 44128 : if (standbyState <= STANDBY_INITIALIZED)
4405 : {
4406 0 : latestObservedXid = xid;
4407 0 : return;
4408 : }
4409 :
4410 : /*
4411 : * Add (latestObservedXid, xid] onto the KnownAssignedXids array.
4412 : */
4413 44128 : next_expected_xid = latestObservedXid;
4414 44128 : TransactionIdAdvance(next_expected_xid);
4415 44128 : KnownAssignedXidsAdd(next_expected_xid, xid, false);
4416 :
4417 : /*
4418 : * Now we can advance latestObservedXid
4419 : */
4420 44128 : latestObservedXid = xid;
4421 :
4422 : /* TransamVariables->nextXid must be beyond any observed xid */
4423 44128 : AdvanceNextFullTransactionIdPastXid(latestObservedXid);
4424 : }
4425 : }
4426 :
4427 : /*
4428 : * ExpireTreeKnownAssignedTransactionIds
4429 : * Remove the given XIDs from KnownAssignedXids.
4430 : *
4431 : * Called during recovery in analogy with and in place of ProcArrayEndTransaction()
4432 : */
4433 : void
4434 42490 : ExpireTreeKnownAssignedTransactionIds(TransactionId xid, int nsubxids,
4435 : TransactionId *subxids, TransactionId max_xid)
4436 : {
4437 : Assert(standbyState >= STANDBY_INITIALIZED);
4438 :
4439 : /*
4440 : * Uses same locking as transaction commit
4441 : */
4442 42490 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
4443 :
4444 42490 : KnownAssignedXidsRemoveTree(xid, nsubxids, subxids);
4445 :
4446 : /* As in ProcArrayEndTransaction, advance latestCompletedXid */
4447 42490 : MaintainLatestCompletedXidRecovery(max_xid);
4448 :
4449 : /* ... and xactCompletionCount */
4450 42490 : TransamVariables->xactCompletionCount++;
4451 :
4452 42490 : LWLockRelease(ProcArrayLock);
4453 42490 : }
4454 :
4455 : /*
4456 : * ExpireAllKnownAssignedTransactionIds
4457 : * Remove all entries in KnownAssignedXids and reset lastOverflowedXid.
4458 : */
4459 : void
4460 212 : ExpireAllKnownAssignedTransactionIds(void)
4461 : {
4462 : FullTransactionId latestXid;
4463 :
4464 212 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
4465 212 : KnownAssignedXidsRemovePreceding(InvalidTransactionId);
4466 :
4467 : /* Reset latestCompletedXid to nextXid - 1 */
4468 : Assert(FullTransactionIdIsValid(TransamVariables->nextXid));
4469 212 : latestXid = TransamVariables->nextXid;
4470 212 : FullTransactionIdRetreat(&latestXid);
4471 212 : TransamVariables->latestCompletedXid = latestXid;
4472 :
4473 : /*
4474 : * Any transactions that were in-progress were effectively aborted, so
4475 : * advance xactCompletionCount.
4476 : */
4477 212 : TransamVariables->xactCompletionCount++;
4478 :
4479 : /*
4480 : * Reset lastOverflowedXid. Currently, lastOverflowedXid has no use after
4481 : * the call of this function. But do this for unification with what
4482 : * ExpireOldKnownAssignedTransactionIds() do.
4483 : */
4484 212 : procArray->lastOverflowedXid = InvalidTransactionId;
4485 212 : LWLockRelease(ProcArrayLock);
4486 212 : }
4487 :
4488 : /*
4489 : * ExpireOldKnownAssignedTransactionIds
4490 : * Remove KnownAssignedXids entries preceding the given XID and
4491 : * potentially reset lastOverflowedXid.
4492 : */
4493 : void
4494 1570 : ExpireOldKnownAssignedTransactionIds(TransactionId xid)
4495 : {
4496 : TransactionId latestXid;
4497 :
4498 1570 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
4499 :
4500 : /* As in ProcArrayEndTransaction, advance latestCompletedXid */
4501 1570 : latestXid = xid;
4502 1570 : TransactionIdRetreat(latestXid);
4503 1570 : MaintainLatestCompletedXidRecovery(latestXid);
4504 :
4505 : /* ... and xactCompletionCount */
4506 1570 : TransamVariables->xactCompletionCount++;
4507 :
4508 : /*
4509 : * Reset lastOverflowedXid if we know all transactions that have been
4510 : * possibly running are being gone. Not doing so could cause an incorrect
4511 : * lastOverflowedXid value, which makes extra snapshots be marked as
4512 : * suboverflowed.
4513 : */
4514 1570 : if (TransactionIdPrecedes(procArray->lastOverflowedXid, xid))
4515 1558 : procArray->lastOverflowedXid = InvalidTransactionId;
4516 1570 : KnownAssignedXidsRemovePreceding(xid);
4517 1570 : LWLockRelease(ProcArrayLock);
4518 1570 : }
4519 :
4520 : /*
4521 : * KnownAssignedTransactionIdsIdleMaintenance
4522 : * Opportunistically do maintenance work when the startup process
4523 : * is about to go idle.
4524 : */
4525 : void
4526 17130 : KnownAssignedTransactionIdsIdleMaintenance(void)
4527 : {
4528 17130 : KnownAssignedXidsCompress(KAX_STARTUP_PROCESS_IDLE, false);
4529 17130 : }
4530 :
4531 :
4532 : /*
4533 : * Private module functions to manipulate KnownAssignedXids
4534 : *
4535 : * There are 5 main uses of the KnownAssignedXids data structure:
4536 : *
4537 : * * backends taking snapshots - all valid XIDs need to be copied out
4538 : * * backends seeking to determine presence of a specific XID
4539 : * * startup process adding new known-assigned XIDs
4540 : * * startup process removing specific XIDs as transactions end
4541 : * * startup process pruning array when special WAL records arrive
4542 : *
4543 : * This data structure is known to be a hot spot during Hot Standby, so we
4544 : * go to some lengths to make these operations as efficient and as concurrent
4545 : * as possible.
4546 : *
4547 : * The XIDs are stored in an array in sorted order --- TransactionIdPrecedes
4548 : * order, to be exact --- to allow binary search for specific XIDs. Note:
4549 : * in general TransactionIdPrecedes would not provide a total order, but
4550 : * we know that the entries present at any instant should not extend across
4551 : * a large enough fraction of XID space to wrap around (the primary would
4552 : * shut down for fear of XID wrap long before that happens). So it's OK to
4553 : * use TransactionIdPrecedes as a binary-search comparator.
4554 : *
4555 : * It's cheap to maintain the sortedness during insertions, since new known
4556 : * XIDs are always reported in XID order; we just append them at the right.
4557 : *
4558 : * To keep individual deletions cheap, we need to allow gaps in the array.
4559 : * This is implemented by marking array elements as valid or invalid using
4560 : * the parallel boolean array KnownAssignedXidsValid[]. A deletion is done
4561 : * by setting KnownAssignedXidsValid[i] to false, *without* clearing the
4562 : * XID entry itself. This preserves the property that the XID entries are
4563 : * sorted, so we can do binary searches easily. Periodically we compress
4564 : * out the unused entries; that's much cheaper than having to compress the
4565 : * array immediately on every deletion.
4566 : *
4567 : * The actually valid items in KnownAssignedXids[] and KnownAssignedXidsValid[]
4568 : * are those with indexes tail <= i < head; items outside this subscript range
4569 : * have unspecified contents. When head reaches the end of the array, we
4570 : * force compression of unused entries rather than wrapping around, since
4571 : * allowing wraparound would greatly complicate the search logic. We maintain
4572 : * an explicit tail pointer so that pruning of old XIDs can be done without
4573 : * immediately moving the array contents. In most cases only a small fraction
4574 : * of the array contains valid entries at any instant.
4575 : *
4576 : * Although only the startup process can ever change the KnownAssignedXids
4577 : * data structure, we still need interlocking so that standby backends will
4578 : * not observe invalid intermediate states. The convention is that backends
4579 : * must hold shared ProcArrayLock to examine the array. To remove XIDs from
4580 : * the array, the startup process must hold ProcArrayLock exclusively, for
4581 : * the usual transactional reasons (compare commit/abort of a transaction
4582 : * during normal running). Compressing unused entries out of the array
4583 : * likewise requires exclusive lock. To add XIDs to the array, we just insert
4584 : * them into slots to the right of the head pointer and then advance the head
4585 : * pointer. This doesn't require any lock at all, but on machines with weak
4586 : * memory ordering, we need to be careful that other processors see the array
4587 : * element changes before they see the head pointer change. We handle this by
4588 : * using memory barriers when reading or writing the head/tail pointers (unless
4589 : * the caller holds ProcArrayLock exclusively).
4590 : *
4591 : * Algorithmic analysis:
4592 : *
4593 : * If we have a maximum of M slots, with N XIDs currently spread across
4594 : * S elements then we have N <= S <= M always.
4595 : *
4596 : * * Adding a new XID is O(1) and needs no lock (unless compression must
4597 : * happen)
4598 : * * Compressing the array is O(S) and requires exclusive lock
4599 : * * Removing an XID is O(logS) and requires exclusive lock
4600 : * * Taking a snapshot is O(S) and requires shared lock
4601 : * * Checking for an XID is O(logS) and requires shared lock
4602 : *
4603 : * In comparison, using a hash table for KnownAssignedXids would mean that
4604 : * taking snapshots would be O(M). If we can maintain S << M then the
4605 : * sorted array technique will deliver significantly faster snapshots.
4606 : * If we try to keep S too small then we will spend too much time compressing,
4607 : * so there is an optimal point for any workload mix. We use a heuristic to
4608 : * decide when to compress the array, though trimming also helps reduce
4609 : * frequency of compressing. The heuristic requires us to track the number of
4610 : * currently valid XIDs in the array (N). Except in special cases, we'll
4611 : * compress when S >= 2N. Bounding S at 2N in turn bounds the time for
4612 : * taking a snapshot to be O(N), which it would have to be anyway.
4613 : */
4614 :
4615 :
4616 : /*
4617 : * Compress KnownAssignedXids by shifting valid data down to the start of the
4618 : * array, removing any gaps.
4619 : *
4620 : * A compression step is forced if "reason" is KAX_NO_SPACE, otherwise
4621 : * we do it only if a heuristic indicates it's a good time to do it.
4622 : *
4623 : * Compression requires holding ProcArrayLock in exclusive mode.
4624 : * Caller must pass haveLock = true if it already holds the lock.
4625 : */
4626 : static void
4627 61232 : KnownAssignedXidsCompress(KAXCompressReason reason, bool haveLock)
4628 : {
4629 61232 : ProcArrayStruct *pArray = procArray;
4630 : int head,
4631 : tail,
4632 : nelements;
4633 : int compress_index;
4634 : int i;
4635 :
4636 : /* Counters for compression heuristics */
4637 : static unsigned int transactionEndsCounter;
4638 : static TimestampTz lastCompressTs;
4639 :
4640 : /* Tuning constants */
4641 : #define KAX_COMPRESS_FREQUENCY 128 /* in transactions */
4642 : #define KAX_COMPRESS_IDLE_INTERVAL 1000 /* in ms */
4643 :
4644 : /*
4645 : * Since only the startup process modifies the head/tail pointers, we
4646 : * don't need a lock to read them here.
4647 : */
4648 61232 : head = pArray->headKnownAssignedXids;
4649 61232 : tail = pArray->tailKnownAssignedXids;
4650 61232 : nelements = head - tail;
4651 :
4652 : /*
4653 : * If we can choose whether to compress, use a heuristic to avoid
4654 : * compressing too often or not often enough. "Compress" here simply
4655 : * means moving the values to the beginning of the array, so it is not as
4656 : * complex or costly as typical data compression algorithms.
4657 : */
4658 61232 : if (nelements == pArray->numKnownAssignedXids)
4659 : {
4660 : /*
4661 : * When there are no gaps between head and tail, don't bother to
4662 : * compress, except in the KAX_NO_SPACE case where we must compress to
4663 : * create some space after the head.
4664 : */
4665 30612 : if (reason != KAX_NO_SPACE)
4666 30612 : return;
4667 : }
4668 30620 : else if (reason == KAX_TRANSACTION_END)
4669 : {
4670 : /*
4671 : * Consider compressing only once every so many commits. Frequency
4672 : * determined by benchmarks.
4673 : */
4674 26044 : if ((transactionEndsCounter++) % KAX_COMPRESS_FREQUENCY != 0)
4675 25822 : return;
4676 :
4677 : /*
4678 : * Furthermore, compress only if the used part of the array is less
4679 : * than 50% full (see comments above).
4680 : */
4681 222 : if (nelements < 2 * pArray->numKnownAssignedXids)
4682 14 : return;
4683 : }
4684 4576 : else if (reason == KAX_STARTUP_PROCESS_IDLE)
4685 : {
4686 : /*
4687 : * We're about to go idle for lack of new WAL, so we might as well
4688 : * compress. But not too often, to avoid ProcArray lock contention
4689 : * with readers.
4690 : */
4691 4340 : if (lastCompressTs != 0)
4692 : {
4693 : TimestampTz compress_after;
4694 :
4695 4338 : compress_after = TimestampTzPlusMilliseconds(lastCompressTs,
4696 : KAX_COMPRESS_IDLE_INTERVAL);
4697 4338 : if (GetCurrentTimestamp() < compress_after)
4698 4256 : return;
4699 : }
4700 : }
4701 :
4702 : /* Need to compress, so get the lock if we don't have it. */
4703 528 : if (!haveLock)
4704 84 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
4705 :
4706 : /*
4707 : * We compress the array by reading the valid values from tail to head,
4708 : * re-aligning data to 0th element.
4709 : */
4710 528 : compress_index = 0;
4711 18724 : for (i = tail; i < head; i++)
4712 : {
4713 18196 : if (KnownAssignedXidsValid[i])
4714 : {
4715 2048 : KnownAssignedXids[compress_index] = KnownAssignedXids[i];
4716 2048 : KnownAssignedXidsValid[compress_index] = true;
4717 2048 : compress_index++;
4718 : }
4719 : }
4720 : Assert(compress_index == pArray->numKnownAssignedXids);
4721 :
4722 528 : pArray->tailKnownAssignedXids = 0;
4723 528 : pArray->headKnownAssignedXids = compress_index;
4724 :
4725 528 : if (!haveLock)
4726 84 : LWLockRelease(ProcArrayLock);
4727 :
4728 : /* Update timestamp for maintenance. No need to hold lock for this. */
4729 528 : lastCompressTs = GetCurrentTimestamp();
4730 : }
4731 :
4732 : /*
4733 : * Add xids into KnownAssignedXids at the head of the array.
4734 : *
4735 : * xids from from_xid to to_xid, inclusive, are added to the array.
4736 : *
4737 : * If exclusive_lock is true then caller already holds ProcArrayLock in
4738 : * exclusive mode, so we need no extra locking here. Else caller holds no
4739 : * lock, so we need to be sure we maintain sufficient interlocks against
4740 : * concurrent readers. (Only the startup process ever calls this, so no need
4741 : * to worry about concurrent writers.)
4742 : */
4743 : static void
4744 44136 : KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
4745 : bool exclusive_lock)
4746 : {
4747 44136 : ProcArrayStruct *pArray = procArray;
4748 : TransactionId next_xid;
4749 : int head,
4750 : tail;
4751 : int nxids;
4752 : int i;
4753 :
4754 : Assert(TransactionIdPrecedesOrEquals(from_xid, to_xid));
4755 :
4756 : /*
4757 : * Calculate how many array slots we'll need. Normally this is cheap; in
4758 : * the unusual case where the XIDs cross the wrap point, we do it the hard
4759 : * way.
4760 : */
4761 44136 : if (to_xid >= from_xid)
4762 44136 : nxids = to_xid - from_xid + 1;
4763 : else
4764 : {
4765 0 : nxids = 1;
4766 0 : next_xid = from_xid;
4767 0 : while (TransactionIdPrecedes(next_xid, to_xid))
4768 : {
4769 0 : nxids++;
4770 0 : TransactionIdAdvance(next_xid);
4771 : }
4772 : }
4773 :
4774 : /*
4775 : * Since only the startup process modifies the head/tail pointers, we
4776 : * don't need a lock to read them here.
4777 : */
4778 44136 : head = pArray->headKnownAssignedXids;
4779 44136 : tail = pArray->tailKnownAssignedXids;
4780 :
4781 : Assert(head >= 0 && head <= pArray->maxKnownAssignedXids);
4782 : Assert(tail >= 0 && tail < pArray->maxKnownAssignedXids);
4783 :
4784 : /*
4785 : * Verify that insertions occur in TransactionId sequence. Note that even
4786 : * if the last existing element is marked invalid, it must still have a
4787 : * correctly sequenced XID value.
4788 : */
4789 73044 : if (head > tail &&
4790 28908 : TransactionIdFollowsOrEquals(KnownAssignedXids[head - 1], from_xid))
4791 : {
4792 0 : KnownAssignedXidsDisplay(LOG);
4793 0 : elog(ERROR, "out-of-order XID insertion in KnownAssignedXids");
4794 : }
4795 :
4796 : /*
4797 : * If our xids won't fit in the remaining space, compress out free space
4798 : */
4799 44136 : if (head + nxids > pArray->maxKnownAssignedXids)
4800 : {
4801 0 : KnownAssignedXidsCompress(KAX_NO_SPACE, exclusive_lock);
4802 :
4803 0 : head = pArray->headKnownAssignedXids;
4804 : /* note: we no longer care about the tail pointer */
4805 :
4806 : /*
4807 : * If it still won't fit then we're out of memory
4808 : */
4809 0 : if (head + nxids > pArray->maxKnownAssignedXids)
4810 0 : elog(ERROR, "too many KnownAssignedXids");
4811 : }
4812 :
4813 : /* Now we can insert the xids into the space starting at head */
4814 44136 : next_xid = from_xid;
4815 89698 : for (i = 0; i < nxids; i++)
4816 : {
4817 45562 : KnownAssignedXids[head] = next_xid;
4818 45562 : KnownAssignedXidsValid[head] = true;
4819 45562 : TransactionIdAdvance(next_xid);
4820 45562 : head++;
4821 : }
4822 :
4823 : /* Adjust count of number of valid entries */
4824 44136 : pArray->numKnownAssignedXids += nxids;
4825 :
4826 : /*
4827 : * Now update the head pointer. We use a write barrier to ensure that
4828 : * other processors see the above array updates before they see the head
4829 : * pointer change. The barrier isn't required if we're holding
4830 : * ProcArrayLock exclusively.
4831 : */
4832 44136 : if (!exclusive_lock)
4833 44128 : pg_write_barrier();
4834 :
4835 44136 : pArray->headKnownAssignedXids = head;
4836 44136 : }
4837 :
4838 : /*
4839 : * KnownAssignedXidsSearch
4840 : *
4841 : * Searches KnownAssignedXids for a specific xid and optionally removes it.
4842 : * Returns true if it was found, false if not.
4843 : *
4844 : * Caller must hold ProcArrayLock in shared or exclusive mode.
4845 : * Exclusive lock must be held for remove = true.
4846 : */
4847 : static bool
4848 47830 : KnownAssignedXidsSearch(TransactionId xid, bool remove)
4849 : {
4850 47830 : ProcArrayStruct *pArray = procArray;
4851 : int first,
4852 : last;
4853 : int head;
4854 : int tail;
4855 47830 : int result_index = -1;
4856 :
4857 47830 : tail = pArray->tailKnownAssignedXids;
4858 47830 : head = pArray->headKnownAssignedXids;
4859 :
4860 : /*
4861 : * Only the startup process removes entries, so we don't need the read
4862 : * barrier in that case.
4863 : */
4864 47830 : if (!remove)
4865 2 : pg_read_barrier(); /* pairs with KnownAssignedXidsAdd */
4866 :
4867 : /*
4868 : * Standard binary search. Note we can ignore the KnownAssignedXidsValid
4869 : * array here, since even invalid entries will contain sorted XIDs.
4870 : */
4871 47830 : first = tail;
4872 47830 : last = head - 1;
4873 163840 : while (first <= last)
4874 : {
4875 : int mid_index;
4876 : TransactionId mid_xid;
4877 :
4878 161416 : mid_index = (first + last) / 2;
4879 161416 : mid_xid = KnownAssignedXids[mid_index];
4880 :
4881 161416 : if (xid == mid_xid)
4882 : {
4883 45406 : result_index = mid_index;
4884 45406 : break;
4885 : }
4886 116010 : else if (TransactionIdPrecedes(xid, mid_xid))
4887 25074 : last = mid_index - 1;
4888 : else
4889 90936 : first = mid_index + 1;
4890 : }
4891 :
4892 47830 : if (result_index < 0)
4893 2424 : return false; /* not in array */
4894 :
4895 45406 : if (!KnownAssignedXidsValid[result_index])
4896 16 : return false; /* in array, but invalid */
4897 :
4898 45390 : if (remove)
4899 : {
4900 45390 : KnownAssignedXidsValid[result_index] = false;
4901 :
4902 45390 : pArray->numKnownAssignedXids--;
4903 : Assert(pArray->numKnownAssignedXids >= 0);
4904 :
4905 : /*
4906 : * If we're removing the tail element then advance tail pointer over
4907 : * any invalid elements. This will speed future searches.
4908 : */
4909 45390 : if (result_index == tail)
4910 : {
4911 17432 : tail++;
4912 29242 : while (tail < head && !KnownAssignedXidsValid[tail])
4913 11810 : tail++;
4914 17432 : if (tail >= head)
4915 : {
4916 : /* Array is empty, so we can reset both pointers */
4917 15208 : pArray->headKnownAssignedXids = 0;
4918 15208 : pArray->tailKnownAssignedXids = 0;
4919 : }
4920 : else
4921 : {
4922 2224 : pArray->tailKnownAssignedXids = tail;
4923 : }
4924 : }
4925 : }
4926 :
4927 45390 : return true;
4928 : }
4929 :
4930 : /*
4931 : * Is the specified XID present in KnownAssignedXids[]?
4932 : *
4933 : * Caller must hold ProcArrayLock in shared or exclusive mode.
4934 : */
4935 : static bool
4936 2 : KnownAssignedXidExists(TransactionId xid)
4937 : {
4938 : Assert(TransactionIdIsValid(xid));
4939 :
4940 2 : return KnownAssignedXidsSearch(xid, false);
4941 : }
4942 :
4943 : /*
4944 : * Remove the specified XID from KnownAssignedXids[].
4945 : *
4946 : * Caller must hold ProcArrayLock in exclusive mode.
4947 : */
4948 : static void
4949 47828 : KnownAssignedXidsRemove(TransactionId xid)
4950 : {
4951 : Assert(TransactionIdIsValid(xid));
4952 :
4953 47828 : elog(DEBUG4, "remove KnownAssignedXid %u", xid);
4954 :
4955 : /*
4956 : * Note: we cannot consider it an error to remove an XID that's not
4957 : * present. We intentionally remove subxact IDs while processing
4958 : * XLOG_XACT_ASSIGNMENT, to avoid array overflow. Then those XIDs will be
4959 : * removed again when the top-level xact commits or aborts.
4960 : *
4961 : * It might be possible to track such XIDs to distinguish this case from
4962 : * actual errors, but it would be complicated and probably not worth it.
4963 : * So, just ignore the search result.
4964 : */
4965 47828 : (void) KnownAssignedXidsSearch(xid, true);
4966 47828 : }
4967 :
4968 : /*
4969 : * KnownAssignedXidsRemoveTree
4970 : * Remove xid (if it's not InvalidTransactionId) and all the subxids.
4971 : *
4972 : * Caller must hold ProcArrayLock in exclusive mode.
4973 : */
4974 : static void
4975 42532 : KnownAssignedXidsRemoveTree(TransactionId xid, int nsubxids,
4976 : TransactionId *subxids)
4977 : {
4978 : int i;
4979 :
4980 42532 : if (TransactionIdIsValid(xid))
4981 42490 : KnownAssignedXidsRemove(xid);
4982 :
4983 47870 : for (i = 0; i < nsubxids; i++)
4984 5338 : KnownAssignedXidsRemove(subxids[i]);
4985 :
4986 : /* Opportunistically compress the array */
4987 42532 : KnownAssignedXidsCompress(KAX_TRANSACTION_END, true);
4988 42532 : }
4989 :
4990 : /*
4991 : * Prune KnownAssignedXids up to, but *not* including xid. If xid is invalid
4992 : * then clear the whole table.
4993 : *
4994 : * Caller must hold ProcArrayLock in exclusive mode.
4995 : */
4996 : static void
4997 1782 : KnownAssignedXidsRemovePreceding(TransactionId removeXid)
4998 : {
4999 1782 : ProcArrayStruct *pArray = procArray;
5000 1782 : int count = 0;
5001 : int head,
5002 : tail,
5003 : i;
5004 :
5005 1782 : if (!TransactionIdIsValid(removeXid))
5006 : {
5007 212 : elog(DEBUG4, "removing all KnownAssignedXids");
5008 212 : pArray->numKnownAssignedXids = 0;
5009 212 : pArray->headKnownAssignedXids = pArray->tailKnownAssignedXids = 0;
5010 212 : return;
5011 : }
5012 :
5013 1570 : elog(DEBUG4, "prune KnownAssignedXids to %u", removeXid);
5014 :
5015 : /*
5016 : * Mark entries invalid starting at the tail. Since array is sorted, we
5017 : * can stop as soon as we reach an entry >= removeXid.
5018 : */
5019 1570 : tail = pArray->tailKnownAssignedXids;
5020 1570 : head = pArray->headKnownAssignedXids;
5021 :
5022 1570 : for (i = tail; i < head; i++)
5023 : {
5024 408 : if (KnownAssignedXidsValid[i])
5025 : {
5026 408 : TransactionId knownXid = KnownAssignedXids[i];
5027 :
5028 408 : if (TransactionIdFollowsOrEquals(knownXid, removeXid))
5029 408 : break;
5030 :
5031 0 : if (!StandbyTransactionIdIsPrepared(knownXid))
5032 : {
5033 0 : KnownAssignedXidsValid[i] = false;
5034 0 : count++;
5035 : }
5036 : }
5037 : }
5038 :
5039 1570 : pArray->numKnownAssignedXids -= count;
5040 : Assert(pArray->numKnownAssignedXids >= 0);
5041 :
5042 : /*
5043 : * Advance the tail pointer if we've marked the tail item invalid.
5044 : */
5045 1570 : for (i = tail; i < head; i++)
5046 : {
5047 408 : if (KnownAssignedXidsValid[i])
5048 408 : break;
5049 : }
5050 1570 : if (i >= head)
5051 : {
5052 : /* Array is empty, so we can reset both pointers */
5053 1162 : pArray->headKnownAssignedXids = 0;
5054 1162 : pArray->tailKnownAssignedXids = 0;
5055 : }
5056 : else
5057 : {
5058 408 : pArray->tailKnownAssignedXids = i;
5059 : }
5060 :
5061 : /* Opportunistically compress the array */
5062 1570 : KnownAssignedXidsCompress(KAX_PRUNE, true);
5063 : }
5064 :
5065 : /*
5066 : * KnownAssignedXidsGet - Get an array of xids by scanning KnownAssignedXids.
5067 : * We filter out anything >= xmax.
5068 : *
5069 : * Returns the number of XIDs stored into xarray[]. Caller is responsible
5070 : * that array is large enough.
5071 : *
5072 : * Caller must hold ProcArrayLock in (at least) shared mode.
5073 : */
5074 : static int
5075 0 : KnownAssignedXidsGet(TransactionId *xarray, TransactionId xmax)
5076 : {
5077 0 : TransactionId xtmp = InvalidTransactionId;
5078 :
5079 0 : return KnownAssignedXidsGetAndSetXmin(xarray, &xtmp, xmax);
5080 : }
5081 :
5082 : /*
5083 : * KnownAssignedXidsGetAndSetXmin - as KnownAssignedXidsGet, plus
5084 : * we reduce *xmin to the lowest xid value seen if not already lower.
5085 : *
5086 : * Caller must hold ProcArrayLock in (at least) shared mode.
5087 : */
5088 : static int
5089 2076 : KnownAssignedXidsGetAndSetXmin(TransactionId *xarray, TransactionId *xmin,
5090 : TransactionId xmax)
5091 : {
5092 2076 : int count = 0;
5093 : int head,
5094 : tail;
5095 : int i;
5096 :
5097 : /*
5098 : * Fetch head just once, since it may change while we loop. We can stop
5099 : * once we reach the initially seen head, since we are certain that an xid
5100 : * cannot enter and then leave the array while we hold ProcArrayLock. We
5101 : * might miss newly-added xids, but they should be >= xmax so irrelevant
5102 : * anyway.
5103 : */
5104 2076 : tail = procArray->tailKnownAssignedXids;
5105 2076 : head = procArray->headKnownAssignedXids;
5106 :
5107 2076 : pg_read_barrier(); /* pairs with KnownAssignedXidsAdd */
5108 :
5109 2152 : for (i = tail; i < head; i++)
5110 : {
5111 : /* Skip any gaps in the array */
5112 204 : if (KnownAssignedXidsValid[i])
5113 : {
5114 158 : TransactionId knownXid = KnownAssignedXids[i];
5115 :
5116 : /*
5117 : * Update xmin if required. Only the first XID need be checked,
5118 : * since the array is sorted.
5119 : */
5120 314 : if (count == 0 &&
5121 156 : TransactionIdPrecedes(knownXid, *xmin))
5122 30 : *xmin = knownXid;
5123 :
5124 : /*
5125 : * Filter out anything >= xmax, again relying on sorted property
5126 : * of array.
5127 : */
5128 316 : if (TransactionIdIsValid(xmax) &&
5129 158 : TransactionIdFollowsOrEquals(knownXid, xmax))
5130 128 : break;
5131 :
5132 : /* Add knownXid into output array */
5133 30 : xarray[count++] = knownXid;
5134 : }
5135 : }
5136 :
5137 2076 : return count;
5138 : }
5139 :
5140 : /*
5141 : * Get oldest XID in the KnownAssignedXids array, or InvalidTransactionId
5142 : * if nothing there.
5143 : */
5144 : static TransactionId
5145 700 : KnownAssignedXidsGetOldestXmin(void)
5146 : {
5147 : int head,
5148 : tail;
5149 : int i;
5150 :
5151 : /*
5152 : * Fetch head just once, since it may change while we loop.
5153 : */
5154 700 : tail = procArray->tailKnownAssignedXids;
5155 700 : head = procArray->headKnownAssignedXids;
5156 :
5157 700 : pg_read_barrier(); /* pairs with KnownAssignedXidsAdd */
5158 :
5159 700 : for (i = tail; i < head; i++)
5160 : {
5161 : /* Skip any gaps in the array */
5162 288 : if (KnownAssignedXidsValid[i])
5163 288 : return KnownAssignedXids[i];
5164 : }
5165 :
5166 412 : return InvalidTransactionId;
5167 : }
5168 :
5169 : /*
5170 : * Display KnownAssignedXids to provide debug trail
5171 : *
5172 : * Currently this is only called within startup process, so we need no
5173 : * special locking.
5174 : *
5175 : * Note this is pretty expensive, and much of the expense will be incurred
5176 : * even if the elog message will get discarded. It's not currently called
5177 : * in any performance-critical places, however, so no need to be tenser.
5178 : */
5179 : static void
5180 220 : KnownAssignedXidsDisplay(int trace_level)
5181 : {
5182 220 : ProcArrayStruct *pArray = procArray;
5183 : StringInfoData buf;
5184 : int head,
5185 : tail,
5186 : i;
5187 220 : int nxids = 0;
5188 :
5189 220 : tail = pArray->tailKnownAssignedXids;
5190 220 : head = pArray->headKnownAssignedXids;
5191 :
5192 220 : initStringInfo(&buf);
5193 :
5194 236 : for (i = tail; i < head; i++)
5195 : {
5196 16 : if (KnownAssignedXidsValid[i])
5197 : {
5198 16 : nxids++;
5199 16 : appendStringInfo(&buf, "[%d]=%u ", i, KnownAssignedXids[i]);
5200 : }
5201 : }
5202 :
5203 220 : elog(trace_level, "%d KnownAssignedXids (num=%d tail=%d head=%d) %s",
5204 : nxids,
5205 : pArray->numKnownAssignedXids,
5206 : pArray->tailKnownAssignedXids,
5207 : pArray->headKnownAssignedXids,
5208 : buf.data);
5209 :
5210 220 : pfree(buf.data);
5211 220 : }
5212 :
5213 : /*
5214 : * KnownAssignedXidsReset
5215 : * Resets KnownAssignedXids to be empty
5216 : */
5217 : static void
5218 0 : KnownAssignedXidsReset(void)
5219 : {
5220 0 : ProcArrayStruct *pArray = procArray;
5221 :
5222 0 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
5223 :
5224 0 : pArray->numKnownAssignedXids = 0;
5225 0 : pArray->tailKnownAssignedXids = 0;
5226 0 : pArray->headKnownAssignedXids = 0;
5227 :
5228 0 : LWLockRelease(ProcArrayLock);
5229 0 : }
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