Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * multixact.c
4 : * PostgreSQL multi-transaction-log manager
5 : *
6 : * The pg_multixact manager is a pg_xact-like manager that stores an array of
7 : * MultiXactMember for each MultiXactId. It is a fundamental part of the
8 : * shared-row-lock implementation. Each MultiXactMember is comprised of a
9 : * TransactionId and a set of flag bits. The name is a bit historical:
10 : * originally, a MultiXactId consisted of more than one TransactionId (except
11 : * in rare corner cases), hence "multi". Nowadays, however, it's perfectly
12 : * legitimate to have MultiXactIds that only include a single Xid.
13 : *
14 : * The meaning of the flag bits is opaque to this module, but they are mostly
15 : * used in heapam.c to identify lock modes that each of the member transactions
16 : * is holding on any given tuple. This module just contains support to store
17 : * and retrieve the arrays.
18 : *
19 : * We use two SLRU areas, one for storing the offsets at which the data
20 : * starts for each MultiXactId in the other one. This trick allows us to
21 : * store variable length arrays of TransactionIds. (We could alternatively
22 : * use one area containing counts and TransactionIds, with valid MultiXactId
23 : * values pointing at slots containing counts; but that way seems less robust
24 : * since it would get completely confused if someone inquired about a bogus
25 : * MultiXactId that pointed to an intermediate slot containing an XID.)
26 : *
27 : * XLOG interactions: this module generates a record whenever a new OFFSETs or
28 : * MEMBERs page is initialized to zeroes, as well as an
29 : * XLOG_MULTIXACT_CREATE_ID record whenever a new MultiXactId is defined.
30 : * This module ignores the WAL rule "write xlog before data," because it
31 : * suffices that actions recording a MultiXactId in a heap xmax do follow that
32 : * rule. The only way for the MXID to be referenced from any data page is for
33 : * heap_lock_tuple() or heap_update() to have put it there, and each generates
34 : * an XLOG record that must follow ours. The normal LSN interlock between the
35 : * data page and that XLOG record will ensure that our XLOG record reaches
36 : * disk first. If the SLRU members/offsets data reaches disk sooner than the
37 : * XLOG records, we do not care; after recovery, no xmax will refer to it. On
38 : * the flip side, to ensure that all referenced entries _do_ reach disk, this
39 : * module's XLOG records completely rebuild the data entered since the last
40 : * checkpoint. We flush and sync all dirty OFFSETs and MEMBERs pages to disk
41 : * before each checkpoint is considered complete.
42 : *
43 : * Like clog.c, and unlike subtrans.c, we have to preserve state across
44 : * crashes and ensure that MXID and offset numbering increases monotonically
45 : * across a crash. We do this in the same way as it's done for transaction
46 : * IDs: the WAL record is guaranteed to contain evidence of every MXID we
47 : * could need to worry about, and we just make sure that at the end of
48 : * replay, the next-MXID and next-offset counters are at least as large as
49 : * anything we saw during replay.
50 : *
51 : * We are able to remove segments no longer necessary by carefully tracking
52 : * each table's used values: during vacuum, any multixact older than a certain
53 : * value is removed; the cutoff value is stored in pg_class. The minimum value
54 : * across all tables in each database is stored in pg_database, and the global
55 : * minimum across all databases is part of pg_control and is kept in shared
56 : * memory. Whenever that minimum is advanced, the SLRUs are truncated.
57 : *
58 : * When new multixactid values are to be created, care is taken that the
59 : * counter does not fall within the wraparound horizon considering the global
60 : * minimum value.
61 : *
62 : * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
63 : * Portions Copyright (c) 1994, Regents of the University of California
64 : *
65 : * src/backend/access/transam/multixact.c
66 : *
67 : *-------------------------------------------------------------------------
68 : */
69 : #include "postgres.h"
70 :
71 : #include "access/multixact.h"
72 : #include "access/slru.h"
73 : #include "access/transam.h"
74 : #include "access/twophase.h"
75 : #include "access/twophase_rmgr.h"
76 : #include "access/xact.h"
77 : #include "access/xlog.h"
78 : #include "access/xloginsert.h"
79 : #include "catalog/pg_type.h"
80 : #include "commands/dbcommands.h"
81 : #include "funcapi.h"
82 : #include "lib/ilist.h"
83 : #include "miscadmin.h"
84 : #include "pg_trace.h"
85 : #include "postmaster/autovacuum.h"
86 : #include "storage/lmgr.h"
87 : #include "storage/pmsignal.h"
88 : #include "storage/proc.h"
89 : #include "storage/procarray.h"
90 : #include "utils/builtins.h"
91 : #include "utils/memutils.h"
92 : #include "utils/snapmgr.h"
93 :
94 :
95 : /*
96 : * Defines for MultiXactOffset page sizes. A page is the same BLCKSZ as is
97 : * used everywhere else in Postgres.
98 : *
99 : * Note: because MultiXactOffsets are 32 bits and wrap around at 0xFFFFFFFF,
100 : * MultiXact page numbering also wraps around at
101 : * 0xFFFFFFFF/MULTIXACT_OFFSETS_PER_PAGE, and segment numbering at
102 : * 0xFFFFFFFF/MULTIXACT_OFFSETS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need
103 : * take no explicit notice of that fact in this module, except when comparing
104 : * segment and page numbers in TruncateMultiXact (see
105 : * MultiXactOffsetPagePrecedes).
106 : */
107 :
108 : /* We need four bytes per offset */
109 : #define MULTIXACT_OFFSETS_PER_PAGE (BLCKSZ / sizeof(MultiXactOffset))
110 :
111 : #define MultiXactIdToOffsetPage(xid) \
112 : ((xid) / (MultiXactOffset) MULTIXACT_OFFSETS_PER_PAGE)
113 : #define MultiXactIdToOffsetEntry(xid) \
114 : ((xid) % (MultiXactOffset) MULTIXACT_OFFSETS_PER_PAGE)
115 : #define MultiXactIdToOffsetSegment(xid) (MultiXactIdToOffsetPage(xid) / SLRU_PAGES_PER_SEGMENT)
116 :
117 : /*
118 : * The situation for members is a bit more complex: we store one byte of
119 : * additional flag bits for each TransactionId. To do this without getting
120 : * into alignment issues, we store four bytes of flags, and then the
121 : * corresponding 4 Xids. Each such 5-word (20-byte) set we call a "group", and
122 : * are stored as a whole in pages. Thus, with 8kB BLCKSZ, we keep 409 groups
123 : * per page. This wastes 12 bytes per page, but that's OK -- simplicity (and
124 : * performance) trumps space efficiency here.
125 : *
126 : * Note that the "offset" macros work with byte offset, not array indexes, so
127 : * arithmetic must be done using "char *" pointers.
128 : */
129 : /* We need eight bits per xact, so one xact fits in a byte */
130 : #define MXACT_MEMBER_BITS_PER_XACT 8
131 : #define MXACT_MEMBER_FLAGS_PER_BYTE 1
132 : #define MXACT_MEMBER_XACT_BITMASK ((1 << MXACT_MEMBER_BITS_PER_XACT) - 1)
133 :
134 : /* how many full bytes of flags are there in a group? */
135 : #define MULTIXACT_FLAGBYTES_PER_GROUP 4
136 : #define MULTIXACT_MEMBERS_PER_MEMBERGROUP \
137 : (MULTIXACT_FLAGBYTES_PER_GROUP * MXACT_MEMBER_FLAGS_PER_BYTE)
138 : /* size in bytes of a complete group */
139 : #define MULTIXACT_MEMBERGROUP_SIZE \
140 : (sizeof(TransactionId) * MULTIXACT_MEMBERS_PER_MEMBERGROUP + MULTIXACT_FLAGBYTES_PER_GROUP)
141 : #define MULTIXACT_MEMBERGROUPS_PER_PAGE (BLCKSZ / MULTIXACT_MEMBERGROUP_SIZE)
142 : #define MULTIXACT_MEMBERS_PER_PAGE \
143 : (MULTIXACT_MEMBERGROUPS_PER_PAGE * MULTIXACT_MEMBERS_PER_MEMBERGROUP)
144 :
145 : /*
146 : * Because the number of items per page is not a divisor of the last item
147 : * number (member 0xFFFFFFFF), the last segment does not use the maximum number
148 : * of pages, and moreover the last used page therein does not use the same
149 : * number of items as previous pages. (Another way to say it is that the
150 : * 0xFFFFFFFF member is somewhere in the middle of the last page, so the page
151 : * has some empty space after that item.)
152 : *
153 : * This constant is the number of members in the last page of the last segment.
154 : */
155 : #define MAX_MEMBERS_IN_LAST_MEMBERS_PAGE \
156 : ((uint32) ((0xFFFFFFFF % MULTIXACT_MEMBERS_PER_PAGE) + 1))
157 :
158 : /* page in which a member is to be found */
159 : #define MXOffsetToMemberPage(xid) ((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_PAGE)
160 : #define MXOffsetToMemberSegment(xid) (MXOffsetToMemberPage(xid) / SLRU_PAGES_PER_SEGMENT)
161 :
162 : /* Location (byte offset within page) of flag word for a given member */
163 : #define MXOffsetToFlagsOffset(xid) \
164 : ((((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_MEMBERGROUP) % \
165 : (TransactionId) MULTIXACT_MEMBERGROUPS_PER_PAGE) * \
166 : (TransactionId) MULTIXACT_MEMBERGROUP_SIZE)
167 : #define MXOffsetToFlagsBitShift(xid) \
168 : (((xid) % (TransactionId) MULTIXACT_MEMBERS_PER_MEMBERGROUP) * \
169 : MXACT_MEMBER_BITS_PER_XACT)
170 :
171 : /* Location (byte offset within page) of TransactionId of given member */
172 : #define MXOffsetToMemberOffset(xid) \
173 : (MXOffsetToFlagsOffset(xid) + MULTIXACT_FLAGBYTES_PER_GROUP + \
174 : ((xid) % MULTIXACT_MEMBERS_PER_MEMBERGROUP) * sizeof(TransactionId))
175 :
176 : /* Multixact members wraparound thresholds. */
177 : #define MULTIXACT_MEMBER_SAFE_THRESHOLD (MaxMultiXactOffset / 2)
178 : #define MULTIXACT_MEMBER_DANGER_THRESHOLD \
179 : (MaxMultiXactOffset - MaxMultiXactOffset / 4)
180 :
181 : #define PreviousMultiXactId(xid) \
182 : ((xid) == FirstMultiXactId ? MaxMultiXactId : (xid) - 1)
183 :
184 : /*
185 : * Links to shared-memory data structures for MultiXact control
186 : */
187 : static SlruCtlData MultiXactOffsetCtlData;
188 : static SlruCtlData MultiXactMemberCtlData;
189 :
190 : #define MultiXactOffsetCtl (&MultiXactOffsetCtlData)
191 : #define MultiXactMemberCtl (&MultiXactMemberCtlData)
192 :
193 : /*
194 : * MultiXact state shared across all backends. All this state is protected
195 : * by MultiXactGenLock. (We also use MultiXactOffsetControlLock and
196 : * MultiXactMemberControlLock to guard accesses to the two sets of SLRU
197 : * buffers. For concurrency's sake, we avoid holding more than one of these
198 : * locks at a time.)
199 : */
200 : typedef struct MultiXactStateData
201 : {
202 : /* next-to-be-assigned MultiXactId */
203 : MultiXactId nextMXact;
204 :
205 : /* next-to-be-assigned offset */
206 : MultiXactOffset nextOffset;
207 :
208 : /* Have we completed multixact startup? */
209 : bool finishedStartup;
210 :
211 : /*
212 : * Oldest multixact that is still potentially referenced by a relation.
213 : * Anything older than this should not be consulted. These values are
214 : * updated by vacuum.
215 : */
216 : MultiXactId oldestMultiXactId;
217 : Oid oldestMultiXactDB;
218 :
219 : /*
220 : * Oldest multixact offset that is potentially referenced by a multixact
221 : * referenced by a relation. We don't always know this value, so there's
222 : * a flag here to indicate whether or not we currently do.
223 : */
224 : MultiXactOffset oldestOffset;
225 : bool oldestOffsetKnown;
226 :
227 : /* support for anti-wraparound measures */
228 : MultiXactId multiVacLimit;
229 : MultiXactId multiWarnLimit;
230 : MultiXactId multiStopLimit;
231 : MultiXactId multiWrapLimit;
232 :
233 : /* support for members anti-wraparound measures */
234 : MultiXactOffset offsetStopLimit; /* known if oldestOffsetKnown */
235 :
236 : /*
237 : * Per-backend data starts here. We have two arrays stored in the area
238 : * immediately following the MultiXactStateData struct. Each is indexed by
239 : * BackendId.
240 : *
241 : * In both arrays, there's a slot for all normal backends (1..MaxBackends)
242 : * followed by a slot for max_prepared_xacts prepared transactions. Valid
243 : * BackendIds start from 1; element zero of each array is never used.
244 : *
245 : * OldestMemberMXactId[k] is the oldest MultiXactId each backend's current
246 : * transaction(s) could possibly be a member of, or InvalidMultiXactId
247 : * when the backend has no live transaction that could possibly be a
248 : * member of a MultiXact. Each backend sets its entry to the current
249 : * nextMXact counter just before first acquiring a shared lock in a given
250 : * transaction, and clears it at transaction end. (This works because only
251 : * during or after acquiring a shared lock could an XID possibly become a
252 : * member of a MultiXact, and that MultiXact would have to be created
253 : * during or after the lock acquisition.)
254 : *
255 : * OldestVisibleMXactId[k] is the oldest MultiXactId each backend's
256 : * current transaction(s) think is potentially live, or InvalidMultiXactId
257 : * when not in a transaction or not in a transaction that's paid any
258 : * attention to MultiXacts yet. This is computed when first needed in a
259 : * given transaction, and cleared at transaction end. We can compute it
260 : * as the minimum of the valid OldestMemberMXactId[] entries at the time
261 : * we compute it (using nextMXact if none are valid). Each backend is
262 : * required not to attempt to access any SLRU data for MultiXactIds older
263 : * than its own OldestVisibleMXactId[] setting; this is necessary because
264 : * the checkpointer could truncate away such data at any instant.
265 : *
266 : * The oldest valid value among all of the OldestMemberMXactId[] and
267 : * OldestVisibleMXactId[] entries is considered by vacuum as the earliest
268 : * possible value still having any live member transaction. Subtracting
269 : * vacuum_multixact_freeze_min_age from that value we obtain the freezing
270 : * point for multixacts for that table. Any value older than that is
271 : * removed from tuple headers (or "frozen"; see FreezeMultiXactId. Note
272 : * that multis that have member xids that are older than the cutoff point
273 : * for xids must also be frozen, even if the multis themselves are newer
274 : * than the multixid cutoff point). Whenever a full table vacuum happens,
275 : * the freezing point so computed is used as the new pg_class.relminmxid
276 : * value. The minimum of all those values in a database is stored as
277 : * pg_database.datminmxid. In turn, the minimum of all of those values is
278 : * stored in pg_control and used as truncation point for pg_multixact. At
279 : * checkpoint or restartpoint, unneeded segments are removed.
280 : */
281 : MultiXactId perBackendXactIds[FLEXIBLE_ARRAY_MEMBER];
282 : } MultiXactStateData;
283 :
284 : /*
285 : * Last element of OldestMemberMXactId and OldestVisibleMXactId arrays.
286 : * Valid elements are (1..MaxOldestSlot); element 0 is never used.
287 : */
288 : #define MaxOldestSlot (MaxBackends + max_prepared_xacts)
289 :
290 : /* Pointers to the state data in shared memory */
291 : static MultiXactStateData *MultiXactState;
292 : static MultiXactId *OldestMemberMXactId;
293 : static MultiXactId *OldestVisibleMXactId;
294 :
295 :
296 : /*
297 : * Definitions for the backend-local MultiXactId cache.
298 : *
299 : * We use this cache to store known MultiXacts, so we don't need to go to
300 : * SLRU areas every time.
301 : *
302 : * The cache lasts for the duration of a single transaction, the rationale
303 : * for this being that most entries will contain our own TransactionId and
304 : * so they will be uninteresting by the time our next transaction starts.
305 : * (XXX not clear that this is correct --- other members of the MultiXact
306 : * could hang around longer than we did. However, it's not clear what a
307 : * better policy for flushing old cache entries would be.) FIXME actually
308 : * this is plain wrong now that multixact's may contain update Xids.
309 : *
310 : * We allocate the cache entries in a memory context that is deleted at
311 : * transaction end, so we don't need to do retail freeing of entries.
312 : */
313 : typedef struct mXactCacheEnt
314 : {
315 : MultiXactId multi;
316 : int nmembers;
317 : dlist_node node;
318 : MultiXactMember members[FLEXIBLE_ARRAY_MEMBER];
319 : } mXactCacheEnt;
320 :
321 : #define MAX_CACHE_ENTRIES 256
322 : static dlist_head MXactCache = DLIST_STATIC_INIT(MXactCache);
323 : static int MXactCacheMembers = 0;
324 : static MemoryContext MXactContext = NULL;
325 :
326 : #ifdef MULTIXACT_DEBUG
327 : #define debug_elog2(a,b) elog(a,b)
328 : #define debug_elog3(a,b,c) elog(a,b,c)
329 : #define debug_elog4(a,b,c,d) elog(a,b,c,d)
330 : #define debug_elog5(a,b,c,d,e) elog(a,b,c,d,e)
331 : #define debug_elog6(a,b,c,d,e,f) elog(a,b,c,d,e,f)
332 : #else
333 : #define debug_elog2(a,b)
334 : #define debug_elog3(a,b,c)
335 : #define debug_elog4(a,b,c,d)
336 : #define debug_elog5(a,b,c,d,e)
337 : #define debug_elog6(a,b,c,d,e,f)
338 : #endif
339 :
340 : /* internal MultiXactId management */
341 : static void MultiXactIdSetOldestVisible(void);
342 : static void RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset,
343 : int nmembers, MultiXactMember *members);
344 : static MultiXactId GetNewMultiXactId(int nmembers, MultiXactOffset *offset);
345 :
346 : /* MultiXact cache management */
347 : static int mxactMemberComparator(const void *arg1, const void *arg2);
348 : static MultiXactId mXactCacheGetBySet(int nmembers, MultiXactMember *members);
349 : static int mXactCacheGetById(MultiXactId multi, MultiXactMember **members);
350 : static void mXactCachePut(MultiXactId multi, int nmembers,
351 : MultiXactMember *members);
352 :
353 : static char *mxstatus_to_string(MultiXactStatus status);
354 :
355 : /* management of SLRU infrastructure */
356 : static int ZeroMultiXactOffsetPage(int pageno, bool writeXlog);
357 : static int ZeroMultiXactMemberPage(int pageno, bool writeXlog);
358 : static bool MultiXactOffsetPagePrecedes(int page1, int page2);
359 : static bool MultiXactMemberPagePrecedes(int page1, int page2);
360 : static bool MultiXactOffsetPrecedes(MultiXactOffset offset1,
361 : MultiXactOffset offset2);
362 : static void ExtendMultiXactOffset(MultiXactId multi);
363 : static void ExtendMultiXactMember(MultiXactOffset offset, int nmembers);
364 : static bool MultiXactOffsetWouldWrap(MultiXactOffset boundary,
365 : MultiXactOffset start, uint32 distance);
366 : static bool SetOffsetVacuumLimit(bool is_startup);
367 : static bool find_multixact_start(MultiXactId multi, MultiXactOffset *result);
368 : static void WriteMZeroPageXlogRec(int pageno, uint8 info);
369 : static void WriteMTruncateXlogRec(Oid oldestMultiDB,
370 : MultiXactId startTruncOff,
371 : MultiXactId endTruncOff,
372 : MultiXactOffset startTruncMemb,
373 : MultiXactOffset endTruncMemb);
374 :
375 :
376 : /*
377 : * MultiXactIdCreate
378 : * Construct a MultiXactId representing two TransactionIds.
379 : *
380 : * The two XIDs must be different, or be requesting different statuses.
381 : *
382 : * NB - we don't worry about our local MultiXactId cache here, because that
383 : * is handled by the lower-level routines.
384 : */
385 : MultiXactId
386 1896 : MultiXactIdCreate(TransactionId xid1, MultiXactStatus status1,
387 : TransactionId xid2, MultiXactStatus status2)
388 : {
389 : MultiXactId newMulti;
390 : MultiXactMember members[2];
391 :
392 : AssertArg(TransactionIdIsValid(xid1));
393 : AssertArg(TransactionIdIsValid(xid2));
394 :
395 : Assert(!TransactionIdEquals(xid1, xid2) || (status1 != status2));
396 :
397 : /* MultiXactIdSetOldestMember() must have been called already. */
398 : Assert(MultiXactIdIsValid(OldestMemberMXactId[MyBackendId]));
399 :
400 : /*
401 : * Note: unlike MultiXactIdExpand, we don't bother to check that both XIDs
402 : * are still running. In typical usage, xid2 will be our own XID and the
403 : * caller just did a check on xid1, so it'd be wasted effort.
404 : */
405 :
406 1896 : members[0].xid = xid1;
407 1896 : members[0].status = status1;
408 1896 : members[1].xid = xid2;
409 1896 : members[1].status = status2;
410 :
411 1896 : newMulti = MultiXactIdCreateFromMembers(2, members);
412 :
413 : debug_elog3(DEBUG2, "Create: %s",
414 : mxid_to_string(newMulti, 2, members));
415 :
416 1896 : return newMulti;
417 : }
418 :
419 : /*
420 : * MultiXactIdExpand
421 : * Add a TransactionId to a pre-existing MultiXactId.
422 : *
423 : * If the TransactionId is already a member of the passed MultiXactId with the
424 : * same status, just return it as-is.
425 : *
426 : * Note that we do NOT actually modify the membership of a pre-existing
427 : * MultiXactId; instead we create a new one. This is necessary to avoid
428 : * a race condition against code trying to wait for one MultiXactId to finish;
429 : * see notes in heapam.c.
430 : *
431 : * NB - we don't worry about our local MultiXactId cache here, because that
432 : * is handled by the lower-level routines.
433 : *
434 : * Note: It is critical that MultiXactIds that come from an old cluster (i.e.
435 : * one upgraded by pg_upgrade from a cluster older than this feature) are not
436 : * passed in.
437 : */
438 : MultiXactId
439 162 : MultiXactIdExpand(MultiXactId multi, TransactionId xid, MultiXactStatus status)
440 : {
441 : MultiXactId newMulti;
442 : MultiXactMember *members;
443 : MultiXactMember *newMembers;
444 : int nmembers;
445 : int i;
446 : int j;
447 :
448 : AssertArg(MultiXactIdIsValid(multi));
449 : AssertArg(TransactionIdIsValid(xid));
450 :
451 : /* MultiXactIdSetOldestMember() must have been called already. */
452 : Assert(MultiXactIdIsValid(OldestMemberMXactId[MyBackendId]));
453 :
454 : debug_elog5(DEBUG2, "Expand: received multi %u, xid %u status %s",
455 : multi, xid, mxstatus_to_string(status));
456 :
457 : /*
458 : * Note: we don't allow for old multis here. The reason is that the only
459 : * caller of this function does a check that the multixact is no longer
460 : * running.
461 : */
462 162 : nmembers = GetMultiXactIdMembers(multi, &members, false, false);
463 :
464 162 : if (nmembers < 0)
465 : {
466 : MultiXactMember member;
467 :
468 : /*
469 : * The MultiXactId is obsolete. This can only happen if all the
470 : * MultiXactId members stop running between the caller checking and
471 : * passing it to us. It would be better to return that fact to the
472 : * caller, but it would complicate the API and it's unlikely to happen
473 : * too often, so just deal with it by creating a singleton MultiXact.
474 : */
475 0 : member.xid = xid;
476 0 : member.status = status;
477 0 : newMulti = MultiXactIdCreateFromMembers(1, &member);
478 :
479 : debug_elog4(DEBUG2, "Expand: %u has no members, create singleton %u",
480 : multi, newMulti);
481 0 : return newMulti;
482 : }
483 :
484 : /*
485 : * If the TransactionId is already a member of the MultiXactId with the
486 : * same status, just return the existing MultiXactId.
487 : */
488 506 : for (i = 0; i < nmembers; i++)
489 : {
490 434 : if (TransactionIdEquals(members[i].xid, xid) &&
491 90 : (members[i].status == status))
492 : {
493 : debug_elog4(DEBUG2, "Expand: %u is already a member of %u",
494 : xid, multi);
495 0 : pfree(members);
496 0 : return multi;
497 : }
498 : }
499 :
500 : /*
501 : * Determine which of the members of the MultiXactId are still of
502 : * interest. This is any running transaction, and also any transaction
503 : * that grabbed something stronger than just a lock and was committed. (An
504 : * update that aborted is of no interest here; and having more than one
505 : * update Xid in a multixact would cause errors elsewhere.)
506 : *
507 : * Removing dead members is not just an optimization: freezing of tuples
508 : * whose Xmax are multis depends on this behavior.
509 : *
510 : * Note we have the same race condition here as above: j could be 0 at the
511 : * end of the loop.
512 : */
513 162 : newMembers = (MultiXactMember *)
514 162 : palloc(sizeof(MultiXactMember) * (nmembers + 1));
515 :
516 506 : for (i = 0, j = 0; i < nmembers; i++)
517 : {
518 424 : if (TransactionIdIsInProgress(members[i].xid) ||
519 90 : (ISUPDATE_from_mxstatus(members[i].status) &&
520 10 : TransactionIdDidCommit(members[i].xid)))
521 : {
522 264 : newMembers[j].xid = members[i].xid;
523 264 : newMembers[j++].status = members[i].status;
524 : }
525 : }
526 :
527 162 : newMembers[j].xid = xid;
528 162 : newMembers[j++].status = status;
529 162 : newMulti = MultiXactIdCreateFromMembers(j, newMembers);
530 :
531 162 : pfree(members);
532 162 : pfree(newMembers);
533 :
534 : debug_elog3(DEBUG2, "Expand: returning new multi %u", newMulti);
535 :
536 162 : return newMulti;
537 : }
538 :
539 : /*
540 : * MultiXactIdIsRunning
541 : * Returns whether a MultiXactId is "running".
542 : *
543 : * We return true if at least one member of the given MultiXactId is still
544 : * running. Note that a "false" result is certain not to change,
545 : * because it is not legal to add members to an existing MultiXactId.
546 : *
547 : * Caller is expected to have verified that the multixact does not come from
548 : * a pg_upgraded share-locked tuple.
549 : */
550 : bool
551 1712 : MultiXactIdIsRunning(MultiXactId multi, bool isLockOnly)
552 : {
553 : MultiXactMember *members;
554 : int nmembers;
555 : int i;
556 :
557 : debug_elog3(DEBUG2, "IsRunning %u?", multi);
558 :
559 : /*
560 : * "false" here means we assume our callers have checked that the given
561 : * multi cannot possibly come from a pg_upgraded database.
562 : */
563 1712 : nmembers = GetMultiXactIdMembers(multi, &members, false, isLockOnly);
564 :
565 1712 : if (nmembers <= 0)
566 : {
567 : debug_elog2(DEBUG2, "IsRunning: no members");
568 1180 : return false;
569 : }
570 :
571 : /*
572 : * Checking for myself is cheap compared to looking in shared memory;
573 : * return true if any live subtransaction of the current top-level
574 : * transaction is a member.
575 : *
576 : * This is not needed for correctness, it's just a fast path.
577 : */
578 1350 : for (i = 0; i < nmembers; i++)
579 : {
580 1034 : if (TransactionIdIsCurrentTransactionId(members[i].xid))
581 : {
582 : debug_elog3(DEBUG2, "IsRunning: I (%d) am running!", i);
583 216 : pfree(members);
584 216 : return true;
585 : }
586 : }
587 :
588 : /*
589 : * This could be made faster by having another entry point in procarray.c,
590 : * walking the PGPROC array only once for all the members. But in most
591 : * cases nmembers should be small enough that it doesn't much matter.
592 : */
593 590 : for (i = 0; i < nmembers; i++)
594 : {
595 492 : if (TransactionIdIsInProgress(members[i].xid))
596 : {
597 : debug_elog4(DEBUG2, "IsRunning: member %d (%u) is running",
598 : i, members[i].xid);
599 218 : pfree(members);
600 218 : return true;
601 : }
602 : }
603 :
604 98 : pfree(members);
605 :
606 : debug_elog3(DEBUG2, "IsRunning: %u is not running", multi);
607 :
608 98 : return false;
609 : }
610 :
611 : /*
612 : * MultiXactIdSetOldestMember
613 : * Save the oldest MultiXactId this transaction could be a member of.
614 : *
615 : * We set the OldestMemberMXactId for a given transaction the first time it's
616 : * going to do some operation that might require a MultiXactId (tuple lock,
617 : * update or delete). We need to do this even if we end up using a
618 : * TransactionId instead of a MultiXactId, because there is a chance that
619 : * another transaction would add our XID to a MultiXactId.
620 : *
621 : * The value to set is the next-to-be-assigned MultiXactId, so this is meant to
622 : * be called just before doing any such possibly-MultiXactId-able operation.
623 : */
624 : void
625 1888378 : MultiXactIdSetOldestMember(void)
626 : {
627 1888378 : if (!MultiXactIdIsValid(OldestMemberMXactId[MyBackendId]))
628 : {
629 : MultiXactId nextMXact;
630 :
631 : /*
632 : * You might think we don't need to acquire a lock here, since
633 : * fetching and storing of TransactionIds is probably atomic, but in
634 : * fact we do: suppose we pick up nextMXact and then lose the CPU for
635 : * a long time. Someone else could advance nextMXact, and then
636 : * another someone else could compute an OldestVisibleMXactId that
637 : * would be after the value we are going to store when we get control
638 : * back. Which would be wrong.
639 : *
640 : * Note that a shared lock is sufficient, because it's enough to stop
641 : * someone from advancing nextMXact; and nobody else could be trying
642 : * to write to our OldestMember entry, only reading (and we assume
643 : * storing it is atomic.)
644 : */
645 133770 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
646 :
647 : /*
648 : * We have to beware of the possibility that nextMXact is in the
649 : * wrapped-around state. We don't fix the counter itself here, but we
650 : * must be sure to store a valid value in our array entry.
651 : */
652 133770 : nextMXact = MultiXactState->nextMXact;
653 133770 : if (nextMXact < FirstMultiXactId)
654 0 : nextMXact = FirstMultiXactId;
655 :
656 133770 : OldestMemberMXactId[MyBackendId] = nextMXact;
657 :
658 133770 : LWLockRelease(MultiXactGenLock);
659 :
660 : debug_elog4(DEBUG2, "MultiXact: setting OldestMember[%d] = %u",
661 : MyBackendId, nextMXact);
662 : }
663 1888378 : }
664 :
665 : /*
666 : * MultiXactIdSetOldestVisible
667 : * Save the oldest MultiXactId this transaction considers possibly live.
668 : *
669 : * We set the OldestVisibleMXactId for a given transaction the first time
670 : * it's going to inspect any MultiXactId. Once we have set this, we are
671 : * guaranteed that the checkpointer won't truncate off SLRU data for
672 : * MultiXactIds at or after our OldestVisibleMXactId.
673 : *
674 : * The value to set is the oldest of nextMXact and all the valid per-backend
675 : * OldestMemberMXactId[] entries. Because of the locking we do, we can be
676 : * certain that no subsequent call to MultiXactIdSetOldestMember can set
677 : * an OldestMemberMXactId[] entry older than what we compute here. Therefore
678 : * there is no live transaction, now or later, that can be a member of any
679 : * MultiXactId older than the OldestVisibleMXactId we compute here.
680 : */
681 : static void
682 1544 : MultiXactIdSetOldestVisible(void)
683 : {
684 1544 : if (!MultiXactIdIsValid(OldestVisibleMXactId[MyBackendId]))
685 : {
686 : MultiXactId oldestMXact;
687 : int i;
688 :
689 376 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
690 :
691 : /*
692 : * We have to beware of the possibility that nextMXact is in the
693 : * wrapped-around state. We don't fix the counter itself here, but we
694 : * must be sure to store a valid value in our array entry.
695 : */
696 376 : oldestMXact = MultiXactState->nextMXact;
697 376 : if (oldestMXact < FirstMultiXactId)
698 0 : oldestMXact = FirstMultiXactId;
699 :
700 45896 : for (i = 1; i <= MaxOldestSlot; i++)
701 : {
702 45520 : MultiXactId thisoldest = OldestMemberMXactId[i];
703 :
704 45992 : if (MultiXactIdIsValid(thisoldest) &&
705 472 : MultiXactIdPrecedes(thisoldest, oldestMXact))
706 228 : oldestMXact = thisoldest;
707 : }
708 :
709 376 : OldestVisibleMXactId[MyBackendId] = oldestMXact;
710 :
711 376 : LWLockRelease(MultiXactGenLock);
712 :
713 : debug_elog4(DEBUG2, "MultiXact: setting OldestVisible[%d] = %u",
714 : MyBackendId, oldestMXact);
715 : }
716 1544 : }
717 :
718 : /*
719 : * ReadNextMultiXactId
720 : * Return the next MultiXactId to be assigned, but don't allocate it
721 : */
722 : MultiXactId
723 89266 : ReadNextMultiXactId(void)
724 : {
725 : MultiXactId mxid;
726 :
727 : /* XXX we could presumably do this without a lock. */
728 89266 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
729 89266 : mxid = MultiXactState->nextMXact;
730 89266 : LWLockRelease(MultiXactGenLock);
731 :
732 89266 : if (mxid < FirstMultiXactId)
733 0 : mxid = FirstMultiXactId;
734 :
735 89266 : return mxid;
736 : }
737 :
738 : /*
739 : * MultiXactIdCreateFromMembers
740 : * Make a new MultiXactId from the specified set of members
741 : *
742 : * Make XLOG, SLRU and cache entries for a new MultiXactId, recording the
743 : * given TransactionIds as members. Returns the newly created MultiXactId.
744 : *
745 : * NB: the passed members[] array will be sorted in-place.
746 : */
747 : MultiXactId
748 2060 : MultiXactIdCreateFromMembers(int nmembers, MultiXactMember *members)
749 : {
750 : MultiXactId multi;
751 : MultiXactOffset offset;
752 : xl_multixact_create xlrec;
753 :
754 : debug_elog3(DEBUG2, "Create: %s",
755 : mxid_to_string(InvalidMultiXactId, nmembers, members));
756 :
757 : /*
758 : * See if the same set of members already exists in our cache; if so, just
759 : * re-use that MultiXactId. (Note: it might seem that looking in our
760 : * cache is insufficient, and we ought to search disk to see if a
761 : * duplicate definition already exists. But since we only ever create
762 : * MultiXacts containing our own XID, in most cases any such MultiXacts
763 : * were in fact created by us, and so will be in our cache. There are
764 : * corner cases where someone else added us to a MultiXact without our
765 : * knowledge, but it's not worth checking for.)
766 : */
767 2060 : multi = mXactCacheGetBySet(nmembers, members);
768 2060 : if (MultiXactIdIsValid(multi))
769 : {
770 : debug_elog2(DEBUG2, "Create: in cache!");
771 1566 : return multi;
772 : }
773 :
774 : /* Verify that there is a single update Xid among the given members. */
775 : {
776 : int i;
777 494 : bool has_update = false;
778 :
779 1580 : for (i = 0; i < nmembers; i++)
780 : {
781 1086 : if (ISUPDATE_from_mxstatus(members[i].status))
782 : {
783 224 : if (has_update)
784 0 : elog(ERROR, "new multixact has more than one updating member");
785 224 : has_update = true;
786 : }
787 : }
788 : }
789 :
790 : /*
791 : * Assign the MXID and offsets range to use, and make sure there is space
792 : * in the OFFSETs and MEMBERs files. NB: this routine does
793 : * START_CRIT_SECTION().
794 : *
795 : * Note: unlike MultiXactIdCreate and MultiXactIdExpand, we do not check
796 : * that we've called MultiXactIdSetOldestMember here. This is because
797 : * this routine is used in some places to create new MultiXactIds of which
798 : * the current backend is not a member, notably during freezing of multis
799 : * in vacuum. During vacuum, in particular, it would be unacceptable to
800 : * keep OldestMulti set, in case it runs for long.
801 : */
802 494 : multi = GetNewMultiXactId(nmembers, &offset);
803 :
804 : /* Make an XLOG entry describing the new MXID. */
805 494 : xlrec.mid = multi;
806 494 : xlrec.moff = offset;
807 494 : xlrec.nmembers = nmembers;
808 :
809 : /*
810 : * XXX Note: there's a lot of padding space in MultiXactMember. We could
811 : * find a more compact representation of this Xlog record -- perhaps all
812 : * the status flags in one XLogRecData, then all the xids in another one?
813 : * Not clear that it's worth the trouble though.
814 : */
815 494 : XLogBeginInsert();
816 494 : XLogRegisterData((char *) (&xlrec), SizeOfMultiXactCreate);
817 494 : XLogRegisterData((char *) members, nmembers * sizeof(MultiXactMember));
818 :
819 494 : (void) XLogInsert(RM_MULTIXACT_ID, XLOG_MULTIXACT_CREATE_ID);
820 :
821 : /* Now enter the information into the OFFSETs and MEMBERs logs */
822 494 : RecordNewMultiXact(multi, offset, nmembers, members);
823 :
824 : /* Done with critical section */
825 494 : END_CRIT_SECTION();
826 :
827 : /* Store the new MultiXactId in the local cache, too */
828 494 : mXactCachePut(multi, nmembers, members);
829 :
830 : debug_elog2(DEBUG2, "Create: all done");
831 :
832 494 : return multi;
833 : }
834 :
835 : /*
836 : * RecordNewMultiXact
837 : * Write info about a new multixact into the offsets and members files
838 : *
839 : * This is broken out of MultiXactIdCreateFromMembers so that xlog replay can
840 : * use it.
841 : */
842 : static void
843 494 : RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset,
844 : int nmembers, MultiXactMember *members)
845 : {
846 : int pageno;
847 : int prev_pageno;
848 : int entryno;
849 : int slotno;
850 : MultiXactOffset *offptr;
851 : int i;
852 :
853 494 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
854 :
855 494 : pageno = MultiXactIdToOffsetPage(multi);
856 494 : entryno = MultiXactIdToOffsetEntry(multi);
857 :
858 : /*
859 : * Note: we pass the MultiXactId to SimpleLruReadPage as the "transaction"
860 : * to complain about if there's any I/O error. This is kinda bogus, but
861 : * since the errors will always give the full pathname, it should be clear
862 : * enough that a MultiXactId is really involved. Perhaps someday we'll
863 : * take the trouble to generalize the slru.c error reporting code.
864 : */
865 494 : slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi);
866 494 : offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
867 494 : offptr += entryno;
868 :
869 494 : *offptr = offset;
870 :
871 494 : MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
872 :
873 : /* Exchange our lock */
874 494 : LWLockRelease(MultiXactOffsetControlLock);
875 :
876 494 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
877 :
878 494 : prev_pageno = -1;
879 :
880 1580 : for (i = 0; i < nmembers; i++, offset++)
881 : {
882 : TransactionId *memberptr;
883 : uint32 *flagsptr;
884 : uint32 flagsval;
885 : int bshift;
886 : int flagsoff;
887 : int memberoff;
888 :
889 : Assert(members[i].status <= MultiXactStatusUpdate);
890 :
891 1086 : pageno = MXOffsetToMemberPage(offset);
892 1086 : memberoff = MXOffsetToMemberOffset(offset);
893 1086 : flagsoff = MXOffsetToFlagsOffset(offset);
894 1086 : bshift = MXOffsetToFlagsBitShift(offset);
895 :
896 1086 : if (pageno != prev_pageno)
897 : {
898 494 : slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi);
899 494 : prev_pageno = pageno;
900 : }
901 :
902 1086 : memberptr = (TransactionId *)
903 1086 : (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
904 :
905 1086 : *memberptr = members[i].xid;
906 :
907 1086 : flagsptr = (uint32 *)
908 1086 : (MultiXactMemberCtl->shared->page_buffer[slotno] + flagsoff);
909 :
910 1086 : flagsval = *flagsptr;
911 1086 : flagsval &= ~(((1 << MXACT_MEMBER_BITS_PER_XACT) - 1) << bshift);
912 1086 : flagsval |= (members[i].status << bshift);
913 1086 : *flagsptr = flagsval;
914 :
915 1086 : MultiXactMemberCtl->shared->page_dirty[slotno] = true;
916 : }
917 :
918 494 : LWLockRelease(MultiXactMemberControlLock);
919 494 : }
920 :
921 : /*
922 : * GetNewMultiXactId
923 : * Get the next MultiXactId.
924 : *
925 : * Also, reserve the needed amount of space in the "members" area. The
926 : * starting offset of the reserved space is returned in *offset.
927 : *
928 : * This may generate XLOG records for expansion of the offsets and/or members
929 : * files. Unfortunately, we have to do that while holding MultiXactGenLock
930 : * to avoid race conditions --- the XLOG record for zeroing a page must appear
931 : * before any backend can possibly try to store data in that page!
932 : *
933 : * We start a critical section before advancing the shared counters. The
934 : * caller must end the critical section after writing SLRU data.
935 : */
936 : static MultiXactId
937 494 : GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
938 : {
939 : MultiXactId result;
940 : MultiXactOffset nextOffset;
941 :
942 : debug_elog3(DEBUG2, "GetNew: for %d xids", nmembers);
943 :
944 : /* safety check, we should never get this far in a HS standby */
945 494 : if (RecoveryInProgress())
946 0 : elog(ERROR, "cannot assign MultiXactIds during recovery");
947 :
948 494 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
949 :
950 : /* Handle wraparound of the nextMXact counter */
951 494 : if (MultiXactState->nextMXact < FirstMultiXactId)
952 0 : MultiXactState->nextMXact = FirstMultiXactId;
953 :
954 : /* Assign the MXID */
955 494 : result = MultiXactState->nextMXact;
956 :
957 : /*----------
958 : * Check to see if it's safe to assign another MultiXactId. This protects
959 : * against catastrophic data loss due to multixact wraparound. The basic
960 : * rules are:
961 : *
962 : * If we're past multiVacLimit or the safe threshold for member storage
963 : * space, or we don't know what the safe threshold for member storage is,
964 : * start trying to force autovacuum cycles.
965 : * If we're past multiWarnLimit, start issuing warnings.
966 : * If we're past multiStopLimit, refuse to create new MultiXactIds.
967 : *
968 : * Note these are pretty much the same protections in GetNewTransactionId.
969 : *----------
970 : */
971 494 : if (!MultiXactIdPrecedes(result, MultiXactState->multiVacLimit))
972 : {
973 : /*
974 : * For safety's sake, we release MultiXactGenLock while sending
975 : * signals, warnings, etc. This is not so much because we care about
976 : * preserving concurrency in this situation, as to avoid any
977 : * possibility of deadlock while doing get_database_name(). First,
978 : * copy all the shared values we'll need in this path.
979 : */
980 0 : MultiXactId multiWarnLimit = MultiXactState->multiWarnLimit;
981 0 : MultiXactId multiStopLimit = MultiXactState->multiStopLimit;
982 0 : MultiXactId multiWrapLimit = MultiXactState->multiWrapLimit;
983 0 : Oid oldest_datoid = MultiXactState->oldestMultiXactDB;
984 :
985 0 : LWLockRelease(MultiXactGenLock);
986 :
987 0 : if (IsUnderPostmaster &&
988 0 : !MultiXactIdPrecedes(result, multiStopLimit))
989 : {
990 0 : char *oldest_datname = get_database_name(oldest_datoid);
991 :
992 : /*
993 : * Immediately kick autovacuum into action as we're already in
994 : * ERROR territory.
995 : */
996 0 : SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
997 :
998 : /* complain even if that DB has disappeared */
999 0 : if (oldest_datname)
1000 0 : ereport(ERROR,
1001 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1002 : errmsg("database is not accepting commands that generate new MultiXactIds to avoid wraparound data loss in database \"%s\"",
1003 : oldest_datname),
1004 : errhint("Execute a database-wide VACUUM in that database.\n"
1005 : "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
1006 : else
1007 0 : ereport(ERROR,
1008 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1009 : errmsg("database is not accepting commands that generate new MultiXactIds to avoid wraparound data loss in database with OID %u",
1010 : oldest_datoid),
1011 : errhint("Execute a database-wide VACUUM in that database.\n"
1012 : "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
1013 : }
1014 :
1015 : /*
1016 : * To avoid swamping the postmaster with signals, we issue the autovac
1017 : * request only once per 64K multis generated. This still gives
1018 : * plenty of chances before we get into real trouble.
1019 : */
1020 0 : if (IsUnderPostmaster && (result % 65536) == 0)
1021 0 : SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
1022 :
1023 0 : if (!MultiXactIdPrecedes(result, multiWarnLimit))
1024 : {
1025 0 : char *oldest_datname = get_database_name(oldest_datoid);
1026 :
1027 : /* complain even if that DB has disappeared */
1028 0 : if (oldest_datname)
1029 0 : ereport(WARNING,
1030 : (errmsg_plural("database \"%s\" must be vacuumed before %u more MultiXactId is used",
1031 : "database \"%s\" must be vacuumed before %u more MultiXactIds are used",
1032 : multiWrapLimit - result,
1033 : oldest_datname,
1034 : multiWrapLimit - result),
1035 : errhint("Execute a database-wide VACUUM in that database.\n"
1036 : "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
1037 : else
1038 0 : ereport(WARNING,
1039 : (errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
1040 : "database with OID %u must be vacuumed before %u more MultiXactIds are used",
1041 : multiWrapLimit - result,
1042 : oldest_datoid,
1043 : multiWrapLimit - result),
1044 : errhint("Execute a database-wide VACUUM in that database.\n"
1045 : "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
1046 : }
1047 :
1048 : /* Re-acquire lock and start over */
1049 0 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
1050 0 : result = MultiXactState->nextMXact;
1051 0 : if (result < FirstMultiXactId)
1052 0 : result = FirstMultiXactId;
1053 : }
1054 :
1055 : /* Make sure there is room for the MXID in the file. */
1056 494 : ExtendMultiXactOffset(result);
1057 :
1058 : /*
1059 : * Reserve the members space, similarly to above. Also, be careful not to
1060 : * return zero as the starting offset for any multixact. See
1061 : * GetMultiXactIdMembers() for motivation.
1062 : */
1063 494 : nextOffset = MultiXactState->nextOffset;
1064 494 : if (nextOffset == 0)
1065 : {
1066 12 : *offset = 1;
1067 12 : nmembers++; /* allocate member slot 0 too */
1068 : }
1069 : else
1070 482 : *offset = nextOffset;
1071 :
1072 : /*----------
1073 : * Protect against overrun of the members space as well, with the
1074 : * following rules:
1075 : *
1076 : * If we're past offsetStopLimit, refuse to generate more multis.
1077 : * If we're close to offsetStopLimit, emit a warning.
1078 : *
1079 : * Arbitrarily, we start emitting warnings when we're 20 segments or less
1080 : * from offsetStopLimit.
1081 : *
1082 : * Note we haven't updated the shared state yet, so if we fail at this
1083 : * point, the multixact ID we grabbed can still be used by the next guy.
1084 : *
1085 : * Note that there is no point in forcing autovacuum runs here: the
1086 : * multixact freeze settings would have to be reduced for that to have any
1087 : * effect.
1088 : *----------
1089 : */
1090 : #define OFFSET_WARN_SEGMENTS 20
1091 988 : if (MultiXactState->oldestOffsetKnown &&
1092 494 : MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit, nextOffset,
1093 : nmembers))
1094 : {
1095 : /* see comment in the corresponding offsets wraparound case */
1096 0 : SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
1097 :
1098 0 : ereport(ERROR,
1099 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1100 : errmsg("multixact \"members\" limit exceeded"),
1101 : errdetail_plural("This command would create a multixact with %u members, but the remaining space is only enough for %u member.",
1102 : "This command would create a multixact with %u members, but the remaining space is only enough for %u members.",
1103 : MultiXactState->offsetStopLimit - nextOffset - 1,
1104 : nmembers,
1105 : MultiXactState->offsetStopLimit - nextOffset - 1),
1106 : errhint("Execute a database-wide VACUUM in database with OID %u with reduced vacuum_multixact_freeze_min_age and vacuum_multixact_freeze_table_age settings.",
1107 : MultiXactState->oldestMultiXactDB)));
1108 : }
1109 :
1110 : /*
1111 : * Check whether we should kick autovacuum into action, to prevent members
1112 : * wraparound. NB we use a much larger window to trigger autovacuum than
1113 : * just the warning limit. The warning is just a measure of last resort -
1114 : * this is in line with GetNewTransactionId's behaviour.
1115 : */
1116 988 : if (!MultiXactState->oldestOffsetKnown ||
1117 494 : (MultiXactState->nextOffset - MultiXactState->oldestOffset
1118 494 : > MULTIXACT_MEMBER_SAFE_THRESHOLD))
1119 : {
1120 : /*
1121 : * To avoid swamping the postmaster with signals, we issue the autovac
1122 : * request only when crossing a segment boundary. With default
1123 : * compilation settings that's roughly after 50k members. This still
1124 : * gives plenty of chances before we get into real trouble.
1125 : */
1126 0 : if ((MXOffsetToMemberPage(nextOffset) / SLRU_PAGES_PER_SEGMENT) !=
1127 0 : (MXOffsetToMemberPage(nextOffset + nmembers) / SLRU_PAGES_PER_SEGMENT))
1128 0 : SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
1129 : }
1130 :
1131 988 : if (MultiXactState->oldestOffsetKnown &&
1132 494 : MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit,
1133 : nextOffset,
1134 : nmembers + MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT * OFFSET_WARN_SEGMENTS))
1135 0 : ereport(WARNING,
1136 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1137 : errmsg_plural("database with OID %u must be vacuumed before %d more multixact member is used",
1138 : "database with OID %u must be vacuumed before %d more multixact members are used",
1139 : MultiXactState->offsetStopLimit - nextOffset + nmembers,
1140 : MultiXactState->oldestMultiXactDB,
1141 : MultiXactState->offsetStopLimit - nextOffset + nmembers),
1142 : errhint("Execute a database-wide VACUUM in that database with reduced vacuum_multixact_freeze_min_age and vacuum_multixact_freeze_table_age settings.")));
1143 :
1144 494 : ExtendMultiXactMember(nextOffset, nmembers);
1145 :
1146 : /*
1147 : * Critical section from here until caller has written the data into the
1148 : * just-reserved SLRU space; we don't want to error out with a partly
1149 : * written MultiXact structure. (In particular, failing to write our
1150 : * start offset after advancing nextMXact would effectively corrupt the
1151 : * previous MultiXact.)
1152 : */
1153 494 : START_CRIT_SECTION();
1154 :
1155 : /*
1156 : * Advance counters. As in GetNewTransactionId(), this must not happen
1157 : * until after file extension has succeeded!
1158 : *
1159 : * We don't care about MultiXactId wraparound here; it will be handled by
1160 : * the next iteration. But note that nextMXact may be InvalidMultiXactId
1161 : * or the first value on a segment-beginning page after this routine
1162 : * exits, so anyone else looking at the variable must be prepared to deal
1163 : * with either case. Similarly, nextOffset may be zero, but we won't use
1164 : * that as the actual start offset of the next multixact.
1165 : */
1166 494 : (MultiXactState->nextMXact)++;
1167 :
1168 494 : MultiXactState->nextOffset += nmembers;
1169 :
1170 494 : LWLockRelease(MultiXactGenLock);
1171 :
1172 : debug_elog4(DEBUG2, "GetNew: returning %u offset %u", result, *offset);
1173 494 : return result;
1174 : }
1175 :
1176 : /*
1177 : * GetMultiXactIdMembers
1178 : * Return the set of MultiXactMembers that make up a MultiXactId
1179 : *
1180 : * Return value is the number of members found, or -1 if there are none,
1181 : * and *members is set to a newly palloc'ed array of members. It's the
1182 : * caller's responsibility to free it when done with it.
1183 : *
1184 : * from_pgupgrade must be passed as true if and only if only the multixact
1185 : * corresponds to a value from a tuple that was locked in a 9.2-or-older
1186 : * installation and later pg_upgrade'd (that is, the infomask is
1187 : * HEAP_LOCKED_UPGRADED). In this case, we know for certain that no members
1188 : * can still be running, so we return -1 just like for an empty multixact
1189 : * without any further checking. It would be wrong to try to resolve such a
1190 : * multixact: either the multixact is within the current valid multixact
1191 : * range, in which case the returned result would be bogus, or outside that
1192 : * range, in which case an error would be raised.
1193 : *
1194 : * In all other cases, the passed multixact must be within the known valid
1195 : * range, that is, greater to or equal than oldestMultiXactId, and less than
1196 : * nextMXact. Otherwise, an error is raised.
1197 : *
1198 : * onlyLock must be set to true if caller is certain that the given multi
1199 : * is used only to lock tuples; can be false without loss of correctness,
1200 : * but passing a true means we can return quickly without checking for
1201 : * old updates.
1202 : */
1203 : int
1204 5104 : GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members,
1205 : bool from_pgupgrade, bool onlyLock)
1206 : {
1207 : int pageno;
1208 : int prev_pageno;
1209 : int entryno;
1210 : int slotno;
1211 : MultiXactOffset *offptr;
1212 : MultiXactOffset offset;
1213 : int length;
1214 : int truelength;
1215 : int i;
1216 : MultiXactId oldestMXact;
1217 : MultiXactId nextMXact;
1218 : MultiXactId tmpMXact;
1219 : MultiXactOffset nextOffset;
1220 : MultiXactMember *ptr;
1221 :
1222 : debug_elog3(DEBUG2, "GetMembers: asked for %u", multi);
1223 :
1224 5104 : if (!MultiXactIdIsValid(multi) || from_pgupgrade)
1225 0 : return -1;
1226 :
1227 : /* See if the MultiXactId is in the local cache */
1228 5104 : length = mXactCacheGetById(multi, members);
1229 5104 : if (length >= 0)
1230 : {
1231 : debug_elog3(DEBUG2, "GetMembers: found %s in the cache",
1232 : mxid_to_string(multi, length, *members));
1233 3560 : return length;
1234 : }
1235 :
1236 : /* Set our OldestVisibleMXactId[] entry if we didn't already */
1237 1544 : MultiXactIdSetOldestVisible();
1238 :
1239 : /*
1240 : * If we know the multi is used only for locking and not for updates, then
1241 : * we can skip checking if the value is older than our oldest visible
1242 : * multi. It cannot possibly still be running.
1243 : */
1244 2888 : if (onlyLock &&
1245 1344 : MultiXactIdPrecedes(multi, OldestVisibleMXactId[MyBackendId]))
1246 : {
1247 : debug_elog2(DEBUG2, "GetMembers: a locker-only multi is too old");
1248 1182 : *members = NULL;
1249 1182 : return -1;
1250 : }
1251 :
1252 : /*
1253 : * We check known limits on MultiXact before resorting to the SLRU area.
1254 : *
1255 : * An ID older than MultiXactState->oldestMultiXactId cannot possibly be
1256 : * useful; it has already been removed, or will be removed shortly, by
1257 : * truncation. If one is passed, an error is raised.
1258 : *
1259 : * Also, an ID >= nextMXact shouldn't ever be seen here; if it is seen, it
1260 : * implies undetected ID wraparound has occurred. This raises a hard
1261 : * error.
1262 : *
1263 : * Shared lock is enough here since we aren't modifying any global state.
1264 : * Acquire it just long enough to grab the current counter values. We may
1265 : * need both nextMXact and nextOffset; see below.
1266 : */
1267 362 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
1268 :
1269 362 : oldestMXact = MultiXactState->oldestMultiXactId;
1270 362 : nextMXact = MultiXactState->nextMXact;
1271 362 : nextOffset = MultiXactState->nextOffset;
1272 :
1273 362 : LWLockRelease(MultiXactGenLock);
1274 :
1275 362 : if (MultiXactIdPrecedes(multi, oldestMXact))
1276 : {
1277 0 : ereport(ERROR,
1278 : (errcode(ERRCODE_INTERNAL_ERROR),
1279 : errmsg("MultiXactId %u does no longer exist -- apparent wraparound",
1280 : multi)));
1281 : return -1;
1282 : }
1283 :
1284 362 : if (!MultiXactIdPrecedes(multi, nextMXact))
1285 0 : ereport(ERROR,
1286 : (errcode(ERRCODE_INTERNAL_ERROR),
1287 : errmsg("MultiXactId %u has not been created yet -- apparent wraparound",
1288 : multi)));
1289 :
1290 : /*
1291 : * Find out the offset at which we need to start reading MultiXactMembers
1292 : * and the number of members in the multixact. We determine the latter as
1293 : * the difference between this multixact's starting offset and the next
1294 : * one's. However, there are some corner cases to worry about:
1295 : *
1296 : * 1. This multixact may be the latest one created, in which case there is
1297 : * no next one to look at. In this case the nextOffset value we just
1298 : * saved is the correct endpoint.
1299 : *
1300 : * 2. The next multixact may still be in process of being filled in: that
1301 : * is, another process may have done GetNewMultiXactId but not yet written
1302 : * the offset entry for that ID. In that scenario, it is guaranteed that
1303 : * the offset entry for that multixact exists (because GetNewMultiXactId
1304 : * won't release MultiXactGenLock until it does) but contains zero
1305 : * (because we are careful to pre-zero offset pages). Because
1306 : * GetNewMultiXactId will never return zero as the starting offset for a
1307 : * multixact, when we read zero as the next multixact's offset, we know we
1308 : * have this case. We sleep for a bit and try again.
1309 : *
1310 : * 3. Because GetNewMultiXactId increments offset zero to offset one to
1311 : * handle case #2, there is an ambiguity near the point of offset
1312 : * wraparound. If we see next multixact's offset is one, is that our
1313 : * multixact's actual endpoint, or did it end at zero with a subsequent
1314 : * increment? We handle this using the knowledge that if the zero'th
1315 : * member slot wasn't filled, it'll contain zero, and zero isn't a valid
1316 : * transaction ID so it can't be a multixact member. Therefore, if we
1317 : * read a zero from the members array, just ignore it.
1318 : *
1319 : * This is all pretty messy, but the mess occurs only in infrequent corner
1320 : * cases, so it seems better than holding the MultiXactGenLock for a long
1321 : * time on every multixact creation.
1322 : */
1323 : retry:
1324 362 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
1325 :
1326 362 : pageno = MultiXactIdToOffsetPage(multi);
1327 362 : entryno = MultiXactIdToOffsetEntry(multi);
1328 :
1329 362 : slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi);
1330 362 : offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
1331 362 : offptr += entryno;
1332 362 : offset = *offptr;
1333 :
1334 : Assert(offset != 0);
1335 :
1336 : /*
1337 : * Use the same increment rule as GetNewMultiXactId(), that is, don't
1338 : * handle wraparound explicitly until needed.
1339 : */
1340 362 : tmpMXact = multi + 1;
1341 :
1342 362 : if (nextMXact == tmpMXact)
1343 : {
1344 : /* Corner case 1: there is no next multixact */
1345 344 : length = nextOffset - offset;
1346 : }
1347 : else
1348 : {
1349 : MultiXactOffset nextMXOffset;
1350 :
1351 : /* handle wraparound if needed */
1352 18 : if (tmpMXact < FirstMultiXactId)
1353 0 : tmpMXact = FirstMultiXactId;
1354 :
1355 18 : prev_pageno = pageno;
1356 :
1357 18 : pageno = MultiXactIdToOffsetPage(tmpMXact);
1358 18 : entryno = MultiXactIdToOffsetEntry(tmpMXact);
1359 :
1360 18 : if (pageno != prev_pageno)
1361 0 : slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, tmpMXact);
1362 :
1363 18 : offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
1364 18 : offptr += entryno;
1365 18 : nextMXOffset = *offptr;
1366 :
1367 18 : if (nextMXOffset == 0)
1368 : {
1369 : /* Corner case 2: next multixact is still being filled in */
1370 0 : LWLockRelease(MultiXactOffsetControlLock);
1371 0 : CHECK_FOR_INTERRUPTS();
1372 0 : pg_usleep(1000L);
1373 0 : goto retry;
1374 : }
1375 :
1376 18 : length = nextMXOffset - offset;
1377 : }
1378 :
1379 362 : LWLockRelease(MultiXactOffsetControlLock);
1380 :
1381 362 : ptr = (MultiXactMember *) palloc(length * sizeof(MultiXactMember));
1382 362 : *members = ptr;
1383 :
1384 : /* Now get the members themselves. */
1385 362 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
1386 :
1387 362 : truelength = 0;
1388 362 : prev_pageno = -1;
1389 1260 : for (i = 0; i < length; i++, offset++)
1390 : {
1391 : TransactionId *xactptr;
1392 : uint32 *flagsptr;
1393 : int flagsoff;
1394 : int bshift;
1395 : int memberoff;
1396 :
1397 898 : pageno = MXOffsetToMemberPage(offset);
1398 898 : memberoff = MXOffsetToMemberOffset(offset);
1399 :
1400 898 : if (pageno != prev_pageno)
1401 : {
1402 362 : slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi);
1403 362 : prev_pageno = pageno;
1404 : }
1405 :
1406 898 : xactptr = (TransactionId *)
1407 898 : (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
1408 :
1409 898 : if (!TransactionIdIsValid(*xactptr))
1410 : {
1411 : /* Corner case 3: we must be looking at unused slot zero */
1412 : Assert(offset == 0);
1413 0 : continue;
1414 : }
1415 :
1416 898 : flagsoff = MXOffsetToFlagsOffset(offset);
1417 898 : bshift = MXOffsetToFlagsBitShift(offset);
1418 898 : flagsptr = (uint32 *) (MultiXactMemberCtl->shared->page_buffer[slotno] + flagsoff);
1419 :
1420 898 : ptr[truelength].xid = *xactptr;
1421 898 : ptr[truelength].status = (*flagsptr >> bshift) & MXACT_MEMBER_XACT_BITMASK;
1422 898 : truelength++;
1423 : }
1424 :
1425 362 : LWLockRelease(MultiXactMemberControlLock);
1426 :
1427 : /*
1428 : * Copy the result into the local cache.
1429 : */
1430 362 : mXactCachePut(multi, truelength, ptr);
1431 :
1432 : debug_elog3(DEBUG2, "GetMembers: no cache for %s",
1433 : mxid_to_string(multi, truelength, ptr));
1434 362 : return truelength;
1435 : }
1436 :
1437 : /*
1438 : * mxactMemberComparator
1439 : * qsort comparison function for MultiXactMember
1440 : *
1441 : * We can't use wraparound comparison for XIDs because that does not respect
1442 : * the triangle inequality! Any old sort order will do.
1443 : */
1444 : static int
1445 3310 : mxactMemberComparator(const void *arg1, const void *arg2)
1446 : {
1447 3310 : MultiXactMember member1 = *(const MultiXactMember *) arg1;
1448 3310 : MultiXactMember member2 = *(const MultiXactMember *) arg2;
1449 :
1450 3310 : if (member1.xid > member2.xid)
1451 52 : return 1;
1452 3258 : if (member1.xid < member2.xid)
1453 3034 : return -1;
1454 224 : if (member1.status > member2.status)
1455 0 : return 1;
1456 224 : if (member1.status < member2.status)
1457 224 : return -1;
1458 0 : return 0;
1459 : }
1460 :
1461 : /*
1462 : * mXactCacheGetBySet
1463 : * returns a MultiXactId from the cache based on the set of
1464 : * TransactionIds that compose it, or InvalidMultiXactId if
1465 : * none matches.
1466 : *
1467 : * This is helpful, for example, if two transactions want to lock a huge
1468 : * table. By using the cache, the second will use the same MultiXactId
1469 : * for the majority of tuples, thus keeping MultiXactId usage low (saving
1470 : * both I/O and wraparound issues).
1471 : *
1472 : * NB: the passed members array will be sorted in-place.
1473 : */
1474 : static MultiXactId
1475 2060 : mXactCacheGetBySet(int nmembers, MultiXactMember *members)
1476 : {
1477 : dlist_iter iter;
1478 :
1479 : debug_elog3(DEBUG2, "CacheGet: looking for %s",
1480 : mxid_to_string(InvalidMultiXactId, nmembers, members));
1481 :
1482 : /* sort the array so comparison is easy */
1483 2060 : qsort(members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
1484 :
1485 2330 : dlist_foreach(iter, &MXactCache)
1486 : {
1487 1836 : mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
1488 :
1489 1836 : if (entry->nmembers != nmembers)
1490 146 : continue;
1491 :
1492 : /*
1493 : * We assume the cache entries are sorted, and that the unused bits in
1494 : * "status" are zeroed.
1495 : */
1496 1690 : if (memcmp(members, entry->members, nmembers * sizeof(MultiXactMember)) == 0)
1497 : {
1498 : debug_elog3(DEBUG2, "CacheGet: found %u", entry->multi);
1499 1566 : dlist_move_head(&MXactCache, iter.cur);
1500 1566 : return entry->multi;
1501 : }
1502 : }
1503 :
1504 : debug_elog2(DEBUG2, "CacheGet: not found :-(");
1505 494 : return InvalidMultiXactId;
1506 : }
1507 :
1508 : /*
1509 : * mXactCacheGetById
1510 : * returns the composing MultiXactMember set from the cache for a
1511 : * given MultiXactId, if present.
1512 : *
1513 : * If successful, *xids is set to the address of a palloc'd copy of the
1514 : * MultiXactMember set. Return value is number of members, or -1 on failure.
1515 : */
1516 : static int
1517 5104 : mXactCacheGetById(MultiXactId multi, MultiXactMember **members)
1518 : {
1519 : dlist_iter iter;
1520 :
1521 : debug_elog3(DEBUG2, "CacheGet: looking for %u", multi);
1522 :
1523 5456 : dlist_foreach(iter, &MXactCache)
1524 : {
1525 3912 : mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
1526 :
1527 3912 : if (entry->multi == multi)
1528 : {
1529 : MultiXactMember *ptr;
1530 : Size size;
1531 :
1532 3560 : size = sizeof(MultiXactMember) * entry->nmembers;
1533 3560 : ptr = (MultiXactMember *) palloc(size);
1534 3560 : *members = ptr;
1535 :
1536 3560 : memcpy(ptr, entry->members, size);
1537 :
1538 : debug_elog3(DEBUG2, "CacheGet: found %s",
1539 : mxid_to_string(multi,
1540 : entry->nmembers,
1541 : entry->members));
1542 :
1543 : /*
1544 : * Note we modify the list while not using a modifiable iterator.
1545 : * This is acceptable only because we exit the iteration
1546 : * immediately afterwards.
1547 : */
1548 3560 : dlist_move_head(&MXactCache, iter.cur);
1549 :
1550 3560 : return entry->nmembers;
1551 : }
1552 : }
1553 :
1554 : debug_elog2(DEBUG2, "CacheGet: not found");
1555 1544 : return -1;
1556 : }
1557 :
1558 : /*
1559 : * mXactCachePut
1560 : * Add a new MultiXactId and its composing set into the local cache.
1561 : */
1562 : static void
1563 856 : mXactCachePut(MultiXactId multi, int nmembers, MultiXactMember *members)
1564 : {
1565 : mXactCacheEnt *entry;
1566 :
1567 : debug_elog3(DEBUG2, "CachePut: storing %s",
1568 : mxid_to_string(multi, nmembers, members));
1569 :
1570 856 : if (MXactContext == NULL)
1571 : {
1572 : /* The cache only lives as long as the current transaction */
1573 : debug_elog2(DEBUG2, "CachePut: initializing memory context");
1574 630 : MXactContext = AllocSetContextCreate(TopTransactionContext,
1575 : "MultiXact cache context",
1576 : ALLOCSET_SMALL_SIZES);
1577 : }
1578 :
1579 856 : entry = (mXactCacheEnt *)
1580 856 : MemoryContextAlloc(MXactContext,
1581 : offsetof(mXactCacheEnt, members) +
1582 : nmembers * sizeof(MultiXactMember));
1583 :
1584 856 : entry->multi = multi;
1585 856 : entry->nmembers = nmembers;
1586 856 : memcpy(entry->members, members, nmembers * sizeof(MultiXactMember));
1587 :
1588 : /* mXactCacheGetBySet assumes the entries are sorted, so sort them */
1589 856 : qsort(entry->members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
1590 :
1591 856 : dlist_push_head(&MXactCache, &entry->node);
1592 856 : if (MXactCacheMembers++ >= MAX_CACHE_ENTRIES)
1593 : {
1594 : dlist_node *node;
1595 : mXactCacheEnt *entry;
1596 :
1597 0 : node = dlist_tail_node(&MXactCache);
1598 0 : dlist_delete(node);
1599 0 : MXactCacheMembers--;
1600 :
1601 0 : entry = dlist_container(mXactCacheEnt, node, node);
1602 : debug_elog3(DEBUG2, "CachePut: pruning cached multi %u",
1603 : entry->multi);
1604 :
1605 0 : pfree(entry);
1606 : }
1607 856 : }
1608 :
1609 : static char *
1610 0 : mxstatus_to_string(MultiXactStatus status)
1611 : {
1612 0 : switch (status)
1613 : {
1614 : case MultiXactStatusForKeyShare:
1615 0 : return "keysh";
1616 : case MultiXactStatusForShare:
1617 0 : return "sh";
1618 : case MultiXactStatusForNoKeyUpdate:
1619 0 : return "fornokeyupd";
1620 : case MultiXactStatusForUpdate:
1621 0 : return "forupd";
1622 : case MultiXactStatusNoKeyUpdate:
1623 0 : return "nokeyupd";
1624 : case MultiXactStatusUpdate:
1625 0 : return "upd";
1626 : default:
1627 0 : elog(ERROR, "unrecognized multixact status %d", status);
1628 : return "";
1629 : }
1630 : }
1631 :
1632 : char *
1633 0 : mxid_to_string(MultiXactId multi, int nmembers, MultiXactMember *members)
1634 : {
1635 : static char *str = NULL;
1636 : StringInfoData buf;
1637 : int i;
1638 :
1639 0 : if (str != NULL)
1640 0 : pfree(str);
1641 :
1642 0 : initStringInfo(&buf);
1643 :
1644 0 : appendStringInfo(&buf, "%u %d[%u (%s)", multi, nmembers, members[0].xid,
1645 : mxstatus_to_string(members[0].status));
1646 :
1647 0 : for (i = 1; i < nmembers; i++)
1648 0 : appendStringInfo(&buf, ", %u (%s)", members[i].xid,
1649 0 : mxstatus_to_string(members[i].status));
1650 :
1651 0 : appendStringInfoChar(&buf, ']');
1652 0 : str = MemoryContextStrdup(TopMemoryContext, buf.data);
1653 0 : pfree(buf.data);
1654 0 : return str;
1655 : }
1656 :
1657 : /*
1658 : * AtEOXact_MultiXact
1659 : * Handle transaction end for MultiXact
1660 : *
1661 : * This is called at top transaction commit or abort (we don't care which).
1662 : */
1663 : void
1664 458666 : AtEOXact_MultiXact(void)
1665 : {
1666 : /*
1667 : * Reset our OldestMemberMXactId and OldestVisibleMXactId values, both of
1668 : * which should only be valid while within a transaction.
1669 : *
1670 : * We assume that storing a MultiXactId is atomic and so we need not take
1671 : * MultiXactGenLock to do this.
1672 : */
1673 458666 : OldestMemberMXactId[MyBackendId] = InvalidMultiXactId;
1674 458666 : OldestVisibleMXactId[MyBackendId] = InvalidMultiXactId;
1675 :
1676 : /*
1677 : * Discard the local MultiXactId cache. Since MXactContext was created as
1678 : * a child of TopTransactionContext, we needn't delete it explicitly.
1679 : */
1680 458666 : MXactContext = NULL;
1681 458666 : dlist_init(&MXactCache);
1682 458666 : MXactCacheMembers = 0;
1683 458666 : }
1684 :
1685 : /*
1686 : * AtPrepare_MultiXact
1687 : * Save multixact state at 2PC transaction prepare
1688 : *
1689 : * In this phase, we only store our OldestMemberMXactId value in the two-phase
1690 : * state file.
1691 : */
1692 : void
1693 54 : AtPrepare_MultiXact(void)
1694 : {
1695 54 : MultiXactId myOldestMember = OldestMemberMXactId[MyBackendId];
1696 :
1697 54 : if (MultiXactIdIsValid(myOldestMember))
1698 20 : RegisterTwoPhaseRecord(TWOPHASE_RM_MULTIXACT_ID, 0,
1699 : &myOldestMember, sizeof(MultiXactId));
1700 54 : }
1701 :
1702 : /*
1703 : * PostPrepare_MultiXact
1704 : * Clean up after successful PREPARE TRANSACTION
1705 : */
1706 : void
1707 54 : PostPrepare_MultiXact(TransactionId xid)
1708 : {
1709 : MultiXactId myOldestMember;
1710 :
1711 : /*
1712 : * Transfer our OldestMemberMXactId value to the slot reserved for the
1713 : * prepared transaction.
1714 : */
1715 54 : myOldestMember = OldestMemberMXactId[MyBackendId];
1716 54 : if (MultiXactIdIsValid(myOldestMember))
1717 : {
1718 20 : BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid, false);
1719 :
1720 : /*
1721 : * Even though storing MultiXactId is atomic, acquire lock to make
1722 : * sure others see both changes, not just the reset of the slot of the
1723 : * current backend. Using a volatile pointer might suffice, but this
1724 : * isn't a hot spot.
1725 : */
1726 20 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
1727 :
1728 20 : OldestMemberMXactId[dummyBackendId] = myOldestMember;
1729 20 : OldestMemberMXactId[MyBackendId] = InvalidMultiXactId;
1730 :
1731 20 : LWLockRelease(MultiXactGenLock);
1732 : }
1733 :
1734 : /*
1735 : * We don't need to transfer OldestVisibleMXactId value, because the
1736 : * transaction is not going to be looking at any more multixacts once it's
1737 : * prepared.
1738 : *
1739 : * We assume that storing a MultiXactId is atomic and so we need not take
1740 : * MultiXactGenLock to do this.
1741 : */
1742 54 : OldestVisibleMXactId[MyBackendId] = InvalidMultiXactId;
1743 :
1744 : /*
1745 : * Discard the local MultiXactId cache like in AtEOX_MultiXact
1746 : */
1747 54 : MXactContext = NULL;
1748 54 : dlist_init(&MXactCache);
1749 54 : MXactCacheMembers = 0;
1750 54 : }
1751 :
1752 : /*
1753 : * multixact_twophase_recover
1754 : * Recover the state of a prepared transaction at startup
1755 : */
1756 : void
1757 8 : multixact_twophase_recover(TransactionId xid, uint16 info,
1758 : void *recdata, uint32 len)
1759 : {
1760 8 : BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid, false);
1761 : MultiXactId oldestMember;
1762 :
1763 : /*
1764 : * Get the oldest member XID from the state file record, and set it in the
1765 : * OldestMemberMXactId slot reserved for this prepared transaction.
1766 : */
1767 : Assert(len == sizeof(MultiXactId));
1768 8 : oldestMember = *((MultiXactId *) recdata);
1769 :
1770 8 : OldestMemberMXactId[dummyBackendId] = oldestMember;
1771 8 : }
1772 :
1773 : /*
1774 : * multixact_twophase_postcommit
1775 : * Similar to AtEOX_MultiXact but for COMMIT PREPARED
1776 : */
1777 : void
1778 20 : multixact_twophase_postcommit(TransactionId xid, uint16 info,
1779 : void *recdata, uint32 len)
1780 : {
1781 20 : BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid, true);
1782 :
1783 : Assert(len == sizeof(MultiXactId));
1784 :
1785 20 : OldestMemberMXactId[dummyBackendId] = InvalidMultiXactId;
1786 20 : }
1787 :
1788 : /*
1789 : * multixact_twophase_postabort
1790 : * This is actually just the same as the COMMIT case.
1791 : */
1792 : void
1793 10 : multixact_twophase_postabort(TransactionId xid, uint16 info,
1794 : void *recdata, uint32 len)
1795 : {
1796 10 : multixact_twophase_postcommit(xid, info, recdata, len);
1797 10 : }
1798 :
1799 : /*
1800 : * Initialization of shared memory for MultiXact. We use two SLRU areas,
1801 : * thus double memory. Also, reserve space for the shared MultiXactState
1802 : * struct and the per-backend MultiXactId arrays (two of those, too).
1803 : */
1804 : Size
1805 1894 : MultiXactShmemSize(void)
1806 : {
1807 : Size size;
1808 :
1809 : /* We need 2*MaxOldestSlot + 1 perBackendXactIds[] entries */
1810 : #define SHARED_MULTIXACT_STATE_SIZE \
1811 : add_size(offsetof(MultiXactStateData, perBackendXactIds) + sizeof(MultiXactId), \
1812 : mul_size(sizeof(MultiXactId) * 2, MaxOldestSlot))
1813 :
1814 1894 : size = SHARED_MULTIXACT_STATE_SIZE;
1815 1894 : size = add_size(size, SimpleLruShmemSize(NUM_MXACTOFFSET_BUFFERS, 0));
1816 1894 : size = add_size(size, SimpleLruShmemSize(NUM_MXACTMEMBER_BUFFERS, 0));
1817 :
1818 1894 : return size;
1819 : }
1820 :
1821 : void
1822 1890 : MultiXactShmemInit(void)
1823 : {
1824 : bool found;
1825 :
1826 : debug_elog2(DEBUG2, "Shared Memory Init for MultiXact");
1827 :
1828 1890 : MultiXactOffsetCtl->PagePrecedes = MultiXactOffsetPagePrecedes;
1829 1890 : MultiXactMemberCtl->PagePrecedes = MultiXactMemberPagePrecedes;
1830 :
1831 1890 : SimpleLruInit(MultiXactOffsetCtl,
1832 : "multixact_offset", NUM_MXACTOFFSET_BUFFERS, 0,
1833 1890 : MultiXactOffsetControlLock, "pg_multixact/offsets",
1834 : LWTRANCHE_MXACTOFFSET_BUFFERS);
1835 1890 : SimpleLruInit(MultiXactMemberCtl,
1836 : "multixact_member", NUM_MXACTMEMBER_BUFFERS, 0,
1837 1890 : MultiXactMemberControlLock, "pg_multixact/members",
1838 : LWTRANCHE_MXACTMEMBER_BUFFERS);
1839 :
1840 : /* Initialize our shared state struct */
1841 1890 : MultiXactState = ShmemInitStruct("Shared MultiXact State",
1842 1890 : SHARED_MULTIXACT_STATE_SIZE,
1843 : &found);
1844 1890 : if (!IsUnderPostmaster)
1845 : {
1846 : Assert(!found);
1847 :
1848 : /* Make sure we zero out the per-backend state */
1849 1890 : MemSet(MultiXactState, 0, SHARED_MULTIXACT_STATE_SIZE);
1850 : }
1851 : else
1852 : Assert(found);
1853 :
1854 : /*
1855 : * Set up array pointers. Note that perBackendXactIds[0] is wasted space
1856 : * since we only use indexes 1..MaxOldestSlot in each array.
1857 : */
1858 1890 : OldestMemberMXactId = MultiXactState->perBackendXactIds;
1859 1890 : OldestVisibleMXactId = OldestMemberMXactId + MaxOldestSlot;
1860 1890 : }
1861 :
1862 : /*
1863 : * This func must be called ONCE on system install. It creates the initial
1864 : * MultiXact segments. (The MultiXacts directories are assumed to have been
1865 : * created by initdb, and MultiXactShmemInit must have been called already.)
1866 : */
1867 : void
1868 322 : BootStrapMultiXact(void)
1869 : {
1870 : int slotno;
1871 :
1872 322 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
1873 :
1874 : /* Create and zero the first page of the offsets log */
1875 322 : slotno = ZeroMultiXactOffsetPage(0, false);
1876 :
1877 : /* Make sure it's written out */
1878 322 : SimpleLruWritePage(MultiXactOffsetCtl, slotno);
1879 : Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
1880 :
1881 322 : LWLockRelease(MultiXactOffsetControlLock);
1882 :
1883 322 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
1884 :
1885 : /* Create and zero the first page of the members log */
1886 322 : slotno = ZeroMultiXactMemberPage(0, false);
1887 :
1888 : /* Make sure it's written out */
1889 322 : SimpleLruWritePage(MultiXactMemberCtl, slotno);
1890 : Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
1891 :
1892 322 : LWLockRelease(MultiXactMemberControlLock);
1893 322 : }
1894 :
1895 : /*
1896 : * Initialize (or reinitialize) a page of MultiXactOffset to zeroes.
1897 : * If writeXlog is true, also emit an XLOG record saying we did this.
1898 : *
1899 : * The page is not actually written, just set up in shared memory.
1900 : * The slot number of the new page is returned.
1901 : *
1902 : * Control lock must be held at entry, and will be held at exit.
1903 : */
1904 : static int
1905 334 : ZeroMultiXactOffsetPage(int pageno, bool writeXlog)
1906 : {
1907 : int slotno;
1908 :
1909 334 : slotno = SimpleLruZeroPage(MultiXactOffsetCtl, pageno);
1910 :
1911 334 : if (writeXlog)
1912 12 : WriteMZeroPageXlogRec(pageno, XLOG_MULTIXACT_ZERO_OFF_PAGE);
1913 :
1914 334 : return slotno;
1915 : }
1916 :
1917 : /*
1918 : * Ditto, for MultiXactMember
1919 : */
1920 : static int
1921 334 : ZeroMultiXactMemberPage(int pageno, bool writeXlog)
1922 : {
1923 : int slotno;
1924 :
1925 334 : slotno = SimpleLruZeroPage(MultiXactMemberCtl, pageno);
1926 :
1927 334 : if (writeXlog)
1928 12 : WriteMZeroPageXlogRec(pageno, XLOG_MULTIXACT_ZERO_MEM_PAGE);
1929 :
1930 334 : return slotno;
1931 : }
1932 :
1933 : /*
1934 : * MaybeExtendOffsetSlru
1935 : * Extend the offsets SLRU area, if necessary
1936 : *
1937 : * After a binary upgrade from <= 9.2, the pg_multixact/offsets SLRU area might
1938 : * contain files that are shorter than necessary; this would occur if the old
1939 : * installation had used multixacts beyond the first page (files cannot be
1940 : * copied, because the on-disk representation is different). pg_upgrade would
1941 : * update pg_control to set the next offset value to be at that position, so
1942 : * that tuples marked as locked by such MultiXacts would be seen as visible
1943 : * without having to consult multixact. However, trying to create and use a
1944 : * new MultiXactId would result in an error because the page on which the new
1945 : * value would reside does not exist. This routine is in charge of creating
1946 : * such pages.
1947 : */
1948 : static void
1949 8 : MaybeExtendOffsetSlru(void)
1950 : {
1951 : int pageno;
1952 :
1953 8 : pageno = MultiXactIdToOffsetPage(MultiXactState->nextMXact);
1954 :
1955 8 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
1956 :
1957 8 : if (!SimpleLruDoesPhysicalPageExist(MultiXactOffsetCtl, pageno))
1958 : {
1959 : int slotno;
1960 :
1961 : /*
1962 : * Fortunately for us, SimpleLruWritePage is already prepared to deal
1963 : * with creating a new segment file even if the page we're writing is
1964 : * not the first in it, so this is enough.
1965 : */
1966 0 : slotno = ZeroMultiXactOffsetPage(pageno, false);
1967 0 : SimpleLruWritePage(MultiXactOffsetCtl, slotno);
1968 : }
1969 :
1970 8 : LWLockRelease(MultiXactOffsetControlLock);
1971 8 : }
1972 :
1973 : /*
1974 : * This must be called ONCE during postmaster or standalone-backend startup.
1975 : *
1976 : * StartupXLOG has already established nextMXact/nextOffset by calling
1977 : * MultiXactSetNextMXact and/or MultiXactAdvanceNextMXact, and the oldestMulti
1978 : * info from pg_control and/or MultiXactAdvanceOldest, but we haven't yet
1979 : * replayed WAL.
1980 : */
1981 : void
1982 1192 : StartupMultiXact(void)
1983 : {
1984 1192 : MultiXactId multi = MultiXactState->nextMXact;
1985 1192 : MultiXactOffset offset = MultiXactState->nextOffset;
1986 : int pageno;
1987 :
1988 : /*
1989 : * Initialize offset's idea of the latest page number.
1990 : */
1991 1192 : pageno = MultiXactIdToOffsetPage(multi);
1992 1192 : MultiXactOffsetCtl->shared->latest_page_number = pageno;
1993 :
1994 : /*
1995 : * Initialize member's idea of the latest page number.
1996 : */
1997 1192 : pageno = MXOffsetToMemberPage(offset);
1998 1192 : MultiXactMemberCtl->shared->latest_page_number = pageno;
1999 1192 : }
2000 :
2001 : /*
2002 : * This must be called ONCE at the end of startup/recovery.
2003 : */
2004 : void
2005 1170 : TrimMultiXact(void)
2006 : {
2007 : MultiXactId nextMXact;
2008 : MultiXactOffset offset;
2009 : MultiXactId oldestMXact;
2010 : Oid oldestMXactDB;
2011 : int pageno;
2012 : int entryno;
2013 : int flagsoff;
2014 :
2015 1170 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2016 1170 : nextMXact = MultiXactState->nextMXact;
2017 1170 : offset = MultiXactState->nextOffset;
2018 1170 : oldestMXact = MultiXactState->oldestMultiXactId;
2019 1170 : oldestMXactDB = MultiXactState->oldestMultiXactDB;
2020 1170 : LWLockRelease(MultiXactGenLock);
2021 :
2022 : /* Clean up offsets state */
2023 1170 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
2024 :
2025 : /*
2026 : * (Re-)Initialize our idea of the latest page number for offsets.
2027 : */
2028 1170 : pageno = MultiXactIdToOffsetPage(nextMXact);
2029 1170 : MultiXactOffsetCtl->shared->latest_page_number = pageno;
2030 :
2031 : /*
2032 : * Zero out the remainder of the current offsets page. See notes in
2033 : * TrimCLOG() for background. Unlike CLOG, some WAL record covers every
2034 : * pg_multixact SLRU mutation. Since, also unlike CLOG, we ignore the WAL
2035 : * rule "write xlog before data," nextMXact successors may carry obsolete,
2036 : * nonzero offset values. Zero those so case 2 of GetMultiXactIdMembers()
2037 : * operates normally.
2038 : */
2039 1170 : entryno = MultiXactIdToOffsetEntry(nextMXact);
2040 1170 : if (entryno != 0)
2041 : {
2042 : int slotno;
2043 : MultiXactOffset *offptr;
2044 :
2045 1170 : slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, nextMXact);
2046 1170 : offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
2047 1170 : offptr += entryno;
2048 :
2049 1170 : MemSet(offptr, 0, BLCKSZ - (entryno * sizeof(MultiXactOffset)));
2050 :
2051 1170 : MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
2052 : }
2053 :
2054 1170 : LWLockRelease(MultiXactOffsetControlLock);
2055 :
2056 : /* And the same for members */
2057 1170 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
2058 :
2059 : /*
2060 : * (Re-)Initialize our idea of the latest page number for members.
2061 : */
2062 1170 : pageno = MXOffsetToMemberPage(offset);
2063 1170 : MultiXactMemberCtl->shared->latest_page_number = pageno;
2064 :
2065 : /*
2066 : * Zero out the remainder of the current members page. See notes in
2067 : * TrimCLOG() for motivation.
2068 : */
2069 1170 : flagsoff = MXOffsetToFlagsOffset(offset);
2070 1170 : if (flagsoff != 0)
2071 : {
2072 : int slotno;
2073 : TransactionId *xidptr;
2074 : int memberoff;
2075 :
2076 8 : memberoff = MXOffsetToMemberOffset(offset);
2077 8 : slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, offset);
2078 8 : xidptr = (TransactionId *)
2079 8 : (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
2080 :
2081 8 : MemSet(xidptr, 0, BLCKSZ - memberoff);
2082 :
2083 : /*
2084 : * Note: we don't need to zero out the flag bits in the remaining
2085 : * members of the current group, because they are always reset before
2086 : * writing.
2087 : */
2088 :
2089 8 : MultiXactMemberCtl->shared->page_dirty[slotno] = true;
2090 : }
2091 :
2092 1170 : LWLockRelease(MultiXactMemberControlLock);
2093 :
2094 : /* signal that we're officially up */
2095 1170 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2096 1170 : MultiXactState->finishedStartup = true;
2097 1170 : LWLockRelease(MultiXactGenLock);
2098 :
2099 : /* Now compute how far away the next members wraparound is. */
2100 1170 : SetMultiXactIdLimit(oldestMXact, oldestMXactDB, true);
2101 1170 : }
2102 :
2103 : /*
2104 : * This must be called ONCE during postmaster or standalone-backend shutdown
2105 : */
2106 : void
2107 1024 : ShutdownMultiXact(void)
2108 : {
2109 : /* Flush dirty MultiXact pages to disk */
2110 : TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_START(false);
2111 1024 : SimpleLruFlush(MultiXactOffsetCtl, false);
2112 1024 : SimpleLruFlush(MultiXactMemberCtl, false);
2113 : TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_DONE(false);
2114 1024 : }
2115 :
2116 : /*
2117 : * Get the MultiXact data to save in a checkpoint record
2118 : */
2119 : void
2120 2816 : MultiXactGetCheckptMulti(bool is_shutdown,
2121 : MultiXactId *nextMulti,
2122 : MultiXactOffset *nextMultiOffset,
2123 : MultiXactId *oldestMulti,
2124 : Oid *oldestMultiDB)
2125 : {
2126 2816 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2127 2816 : *nextMulti = MultiXactState->nextMXact;
2128 2816 : *nextMultiOffset = MultiXactState->nextOffset;
2129 2816 : *oldestMulti = MultiXactState->oldestMultiXactId;
2130 2816 : *oldestMultiDB = MultiXactState->oldestMultiXactDB;
2131 2816 : LWLockRelease(MultiXactGenLock);
2132 :
2133 : debug_elog6(DEBUG2,
2134 : "MultiXact: checkpoint is nextMulti %u, nextOffset %u, oldestMulti %u in DB %u",
2135 : *nextMulti, *nextMultiOffset, *oldestMulti, *oldestMultiDB);
2136 2816 : }
2137 :
2138 : /*
2139 : * Perform a checkpoint --- either during shutdown, or on-the-fly
2140 : */
2141 : void
2142 2832 : CheckPointMultiXact(void)
2143 : {
2144 : TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_START(true);
2145 :
2146 : /* Flush dirty MultiXact pages to disk */
2147 2832 : SimpleLruFlush(MultiXactOffsetCtl, true);
2148 2832 : SimpleLruFlush(MultiXactMemberCtl, true);
2149 :
2150 : TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_DONE(true);
2151 2832 : }
2152 :
2153 : /*
2154 : * Set the next-to-be-assigned MultiXactId and offset
2155 : *
2156 : * This is used when we can determine the correct next ID/offset exactly
2157 : * from a checkpoint record. Although this is only called during bootstrap
2158 : * and XLog replay, we take the lock in case any hot-standby backends are
2159 : * examining the values.
2160 : */
2161 : void
2162 1546 : MultiXactSetNextMXact(MultiXactId nextMulti,
2163 : MultiXactOffset nextMultiOffset)
2164 : {
2165 : debug_elog4(DEBUG2, "MultiXact: setting next multi to %u offset %u",
2166 : nextMulti, nextMultiOffset);
2167 1546 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2168 1546 : MultiXactState->nextMXact = nextMulti;
2169 1546 : MultiXactState->nextOffset = nextMultiOffset;
2170 1546 : LWLockRelease(MultiXactGenLock);
2171 :
2172 : /*
2173 : * During a binary upgrade, make sure that the offsets SLRU is large
2174 : * enough to contain the next value that would be created.
2175 : *
2176 : * We need to do this pretty early during the first startup in binary
2177 : * upgrade mode: before StartupMultiXact() in fact, because this routine
2178 : * is called even before that by StartupXLOG(). And we can't do it
2179 : * earlier than at this point, because during that first call of this
2180 : * routine we determine the MultiXactState->nextMXact value that
2181 : * MaybeExtendOffsetSlru needs.
2182 : */
2183 1546 : if (IsBinaryUpgrade)
2184 8 : MaybeExtendOffsetSlru();
2185 1546 : }
2186 :
2187 : /*
2188 : * Determine the last safe MultiXactId to allocate given the currently oldest
2189 : * datminmxid (ie, the oldest MultiXactId that might exist in any database
2190 : * of our cluster), and the OID of the (or a) database with that value.
2191 : *
2192 : * is_startup is true when we are just starting the cluster, false when we
2193 : * are updating state in a running cluster. This only affects log messages.
2194 : */
2195 : void
2196 3380 : SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid,
2197 : bool is_startup)
2198 : {
2199 : MultiXactId multiVacLimit;
2200 : MultiXactId multiWarnLimit;
2201 : MultiXactId multiStopLimit;
2202 : MultiXactId multiWrapLimit;
2203 : MultiXactId curMulti;
2204 : bool needs_offset_vacuum;
2205 :
2206 : Assert(MultiXactIdIsValid(oldest_datminmxid));
2207 :
2208 : /*
2209 : * We pretend that a wrap will happen halfway through the multixact ID
2210 : * space, but that's not really true, because multixacts wrap differently
2211 : * from transaction IDs. Note that, separately from any concern about
2212 : * multixact IDs wrapping, we must ensure that multixact members do not
2213 : * wrap. Limits for that are set in SetOffsetVacuumLimit, not here.
2214 : */
2215 3380 : multiWrapLimit = oldest_datminmxid + (MaxMultiXactId >> 1);
2216 3380 : if (multiWrapLimit < FirstMultiXactId)
2217 0 : multiWrapLimit += FirstMultiXactId;
2218 :
2219 : /*
2220 : * We'll refuse to continue assigning MultiXactIds once we get within 100
2221 : * multi of data loss.
2222 : *
2223 : * Note: This differs from the magic number used in
2224 : * SetTransactionIdLimit() since vacuum itself will never generate new
2225 : * multis. XXX actually it does, if it needs to freeze old multis.
2226 : */
2227 3380 : multiStopLimit = multiWrapLimit - 100;
2228 3380 : if (multiStopLimit < FirstMultiXactId)
2229 0 : multiStopLimit -= FirstMultiXactId;
2230 :
2231 : /*
2232 : * We'll start complaining loudly when we get within 10M multis of the
2233 : * stop point. This is kind of arbitrary, but if you let your gas gauge
2234 : * get down to 1% of full, would you be looking for the next gas station?
2235 : * We need to be fairly liberal about this number because there are lots
2236 : * of scenarios where most transactions are done by automatic clients that
2237 : * won't pay attention to warnings. (No, we're not gonna make this
2238 : * configurable. If you know enough to configure it, you know enough to
2239 : * not get in this kind of trouble in the first place.)
2240 : */
2241 3380 : multiWarnLimit = multiStopLimit - 10000000;
2242 3380 : if (multiWarnLimit < FirstMultiXactId)
2243 0 : multiWarnLimit -= FirstMultiXactId;
2244 :
2245 : /*
2246 : * We'll start trying to force autovacuums when oldest_datminmxid gets to
2247 : * be more than autovacuum_multixact_freeze_max_age mxids old.
2248 : *
2249 : * Note: autovacuum_multixact_freeze_max_age is a PGC_POSTMASTER parameter
2250 : * so that we don't have to worry about dealing with on-the-fly changes in
2251 : * its value. See SetTransactionIdLimit.
2252 : */
2253 3380 : multiVacLimit = oldest_datminmxid + autovacuum_multixact_freeze_max_age;
2254 3380 : if (multiVacLimit < FirstMultiXactId)
2255 0 : multiVacLimit += FirstMultiXactId;
2256 :
2257 : /* Grab lock for just long enough to set the new limit values */
2258 3380 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2259 3380 : MultiXactState->oldestMultiXactId = oldest_datminmxid;
2260 3380 : MultiXactState->oldestMultiXactDB = oldest_datoid;
2261 3380 : MultiXactState->multiVacLimit = multiVacLimit;
2262 3380 : MultiXactState->multiWarnLimit = multiWarnLimit;
2263 3380 : MultiXactState->multiStopLimit = multiStopLimit;
2264 3380 : MultiXactState->multiWrapLimit = multiWrapLimit;
2265 3380 : curMulti = MultiXactState->nextMXact;
2266 3380 : LWLockRelease(MultiXactGenLock);
2267 :
2268 : /* Log the info */
2269 3380 : ereport(DEBUG1,
2270 : (errmsg("MultiXactId wrap limit is %u, limited by database with OID %u",
2271 : multiWrapLimit, oldest_datoid)));
2272 :
2273 : /*
2274 : * Computing the actual limits is only possible once the data directory is
2275 : * in a consistent state. There's no need to compute the limits while
2276 : * still replaying WAL - no decisions about new multis are made even
2277 : * though multixact creations might be replayed. So we'll only do further
2278 : * checks after TrimMultiXact() has been called.
2279 : */
2280 3380 : if (!MultiXactState->finishedStartup)
2281 1514 : return;
2282 :
2283 : Assert(!InRecovery);
2284 :
2285 : /* Set limits for offset vacuum. */
2286 1866 : needs_offset_vacuum = SetOffsetVacuumLimit(is_startup);
2287 :
2288 : /*
2289 : * If past the autovacuum force point, immediately signal an autovac
2290 : * request. The reason for this is that autovac only processes one
2291 : * database per invocation. Once it's finished cleaning up the oldest
2292 : * database, it'll call here, and we'll signal the postmaster to start
2293 : * another iteration immediately if there are still any old databases.
2294 : */
2295 1866 : if ((MultiXactIdPrecedes(multiVacLimit, curMulti) ||
2296 0 : needs_offset_vacuum) && IsUnderPostmaster)
2297 0 : SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
2298 :
2299 : /* Give an immediate warning if past the wrap warn point */
2300 1866 : if (MultiXactIdPrecedes(multiWarnLimit, curMulti))
2301 : {
2302 : char *oldest_datname;
2303 :
2304 : /*
2305 : * We can be called when not inside a transaction, for example during
2306 : * StartupXLOG(). In such a case we cannot do database access, so we
2307 : * must just report the oldest DB's OID.
2308 : *
2309 : * Note: it's also possible that get_database_name fails and returns
2310 : * NULL, for example because the database just got dropped. We'll
2311 : * still warn, even though the warning might now be unnecessary.
2312 : */
2313 0 : if (IsTransactionState())
2314 0 : oldest_datname = get_database_name(oldest_datoid);
2315 : else
2316 0 : oldest_datname = NULL;
2317 :
2318 0 : if (oldest_datname)
2319 0 : ereport(WARNING,
2320 : (errmsg_plural("database \"%s\" must be vacuumed before %u more MultiXactId is used",
2321 : "database \"%s\" must be vacuumed before %u more MultiXactIds are used",
2322 : multiWrapLimit - curMulti,
2323 : oldest_datname,
2324 : multiWrapLimit - curMulti),
2325 : errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
2326 : "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
2327 : else
2328 0 : ereport(WARNING,
2329 : (errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
2330 : "database with OID %u must be vacuumed before %u more MultiXactIds are used",
2331 : multiWrapLimit - curMulti,
2332 : oldest_datoid,
2333 : multiWrapLimit - curMulti),
2334 : errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
2335 : "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
2336 : }
2337 : }
2338 :
2339 : /*
2340 : * Ensure the next-to-be-assigned MultiXactId is at least minMulti,
2341 : * and similarly nextOffset is at least minMultiOffset.
2342 : *
2343 : * This is used when we can determine minimum safe values from an XLog
2344 : * record (either an on-line checkpoint or an mxact creation log entry).
2345 : * Although this is only called during XLog replay, we take the lock in case
2346 : * any hot-standby backends are examining the values.
2347 : */
2348 : void
2349 128 : MultiXactAdvanceNextMXact(MultiXactId minMulti,
2350 : MultiXactOffset minMultiOffset)
2351 : {
2352 128 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2353 128 : if (MultiXactIdPrecedes(MultiXactState->nextMXact, minMulti))
2354 : {
2355 : debug_elog3(DEBUG2, "MultiXact: setting next multi to %u", minMulti);
2356 0 : MultiXactState->nextMXact = minMulti;
2357 : }
2358 128 : if (MultiXactOffsetPrecedes(MultiXactState->nextOffset, minMultiOffset))
2359 : {
2360 : debug_elog3(DEBUG2, "MultiXact: setting next offset to %u",
2361 : minMultiOffset);
2362 0 : MultiXactState->nextOffset = minMultiOffset;
2363 : }
2364 128 : LWLockRelease(MultiXactGenLock);
2365 128 : }
2366 :
2367 : /*
2368 : * Update our oldestMultiXactId value, but only if it's more recent than what
2369 : * we had.
2370 : *
2371 : * This may only be called during WAL replay.
2372 : */
2373 : void
2374 160 : MultiXactAdvanceOldest(MultiXactId oldestMulti, Oid oldestMultiDB)
2375 : {
2376 : Assert(InRecovery);
2377 :
2378 160 : if (MultiXactIdPrecedes(MultiXactState->oldestMultiXactId, oldestMulti))
2379 0 : SetMultiXactIdLimit(oldestMulti, oldestMultiDB, false);
2380 160 : }
2381 :
2382 : /*
2383 : * Make sure that MultiXactOffset has room for a newly-allocated MultiXactId.
2384 : *
2385 : * NB: this is called while holding MultiXactGenLock. We want it to be very
2386 : * fast most of the time; even when it's not so fast, no actual I/O need
2387 : * happen unless we're forced to write out a dirty log or xlog page to make
2388 : * room in shared memory.
2389 : */
2390 : static void
2391 494 : ExtendMultiXactOffset(MultiXactId multi)
2392 : {
2393 : int pageno;
2394 :
2395 : /*
2396 : * No work except at first MultiXactId of a page. But beware: just after
2397 : * wraparound, the first MultiXactId of page zero is FirstMultiXactId.
2398 : */
2399 494 : if (MultiXactIdToOffsetEntry(multi) != 0 &&
2400 : multi != FirstMultiXactId)
2401 482 : return;
2402 :
2403 12 : pageno = MultiXactIdToOffsetPage(multi);
2404 :
2405 12 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
2406 :
2407 : /* Zero the page and make an XLOG entry about it */
2408 12 : ZeroMultiXactOffsetPage(pageno, true);
2409 :
2410 12 : LWLockRelease(MultiXactOffsetControlLock);
2411 : }
2412 :
2413 : /*
2414 : * Make sure that MultiXactMember has room for the members of a newly-
2415 : * allocated MultiXactId.
2416 : *
2417 : * Like the above routine, this is called while holding MultiXactGenLock;
2418 : * same comments apply.
2419 : */
2420 : static void
2421 494 : ExtendMultiXactMember(MultiXactOffset offset, int nmembers)
2422 : {
2423 : /*
2424 : * It's possible that the members span more than one page of the members
2425 : * file, so we loop to ensure we consider each page. The coding is not
2426 : * optimal if the members span several pages, but that seems unusual
2427 : * enough to not worry much about.
2428 : */
2429 1482 : while (nmembers > 0)
2430 : {
2431 : int flagsoff;
2432 : int flagsbit;
2433 : uint32 difference;
2434 :
2435 : /*
2436 : * Only zero when at first entry of a page.
2437 : */
2438 494 : flagsoff = MXOffsetToFlagsOffset(offset);
2439 494 : flagsbit = MXOffsetToFlagsBitShift(offset);
2440 494 : if (flagsoff == 0 && flagsbit == 0)
2441 : {
2442 : int pageno;
2443 :
2444 12 : pageno = MXOffsetToMemberPage(offset);
2445 :
2446 12 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
2447 :
2448 : /* Zero the page and make an XLOG entry about it */
2449 12 : ZeroMultiXactMemberPage(pageno, true);
2450 :
2451 12 : LWLockRelease(MultiXactMemberControlLock);
2452 : }
2453 :
2454 : /*
2455 : * Compute the number of items till end of current page. Careful: if
2456 : * addition of unsigned ints wraps around, we're at the last page of
2457 : * the last segment; since that page holds a different number of items
2458 : * than other pages, we need to do it differently.
2459 : */
2460 494 : if (offset + MAX_MEMBERS_IN_LAST_MEMBERS_PAGE < offset)
2461 : {
2462 : /*
2463 : * This is the last page of the last segment; we can compute the
2464 : * number of items left to allocate in it without modulo
2465 : * arithmetic.
2466 : */
2467 0 : difference = MaxMultiXactOffset - offset + 1;
2468 : }
2469 : else
2470 494 : difference = MULTIXACT_MEMBERS_PER_PAGE - offset % MULTIXACT_MEMBERS_PER_PAGE;
2471 :
2472 : /*
2473 : * Advance to next page, taking care to properly handle the wraparound
2474 : * case. OK if nmembers goes negative.
2475 : */
2476 494 : nmembers -= difference;
2477 494 : offset += difference;
2478 : }
2479 494 : }
2480 :
2481 : /*
2482 : * GetOldestMultiXactId
2483 : *
2484 : * Return the oldest MultiXactId that's still possibly still seen as live by
2485 : * any running transaction. Older ones might still exist on disk, but they no
2486 : * longer have any running member transaction.
2487 : *
2488 : * It's not safe to truncate MultiXact SLRU segments on the value returned by
2489 : * this function; however, it can be used by a full-table vacuum to set the
2490 : * point at which it will be possible to truncate SLRU for that table.
2491 : */
2492 : MultiXactId
2493 105454 : GetOldestMultiXactId(void)
2494 : {
2495 : MultiXactId oldestMXact;
2496 : MultiXactId nextMXact;
2497 : int i;
2498 :
2499 : /*
2500 : * This is the oldest valid value among all the OldestMemberMXactId[] and
2501 : * OldestVisibleMXactId[] entries, or nextMXact if none are valid.
2502 : */
2503 105454 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2504 :
2505 : /*
2506 : * We have to beware of the possibility that nextMXact is in the
2507 : * wrapped-around state. We don't fix the counter itself here, but we
2508 : * must be sure to use a valid value in our calculation.
2509 : */
2510 105454 : nextMXact = MultiXactState->nextMXact;
2511 105454 : if (nextMXact < FirstMultiXactId)
2512 0 : nextMXact = FirstMultiXactId;
2513 :
2514 105454 : oldestMXact = nextMXact;
2515 12908990 : for (i = 1; i <= MaxOldestSlot; i++)
2516 : {
2517 : MultiXactId thisoldest;
2518 :
2519 12803536 : thisoldest = OldestMemberMXactId[i];
2520 12816342 : if (MultiXactIdIsValid(thisoldest) &&
2521 12806 : MultiXactIdPrecedes(thisoldest, oldestMXact))
2522 30 : oldestMXact = thisoldest;
2523 12803536 : thisoldest = OldestVisibleMXactId[i];
2524 12803548 : if (MultiXactIdIsValid(thisoldest) &&
2525 12 : MultiXactIdPrecedes(thisoldest, oldestMXact))
2526 4 : oldestMXact = thisoldest;
2527 : }
2528 :
2529 105454 : LWLockRelease(MultiXactGenLock);
2530 :
2531 105454 : return oldestMXact;
2532 : }
2533 :
2534 : /*
2535 : * Determine how aggressively we need to vacuum in order to prevent member
2536 : * wraparound.
2537 : *
2538 : * To do so determine what's the oldest member offset and install the limit
2539 : * info in MultiXactState, where it can be used to prevent overrun of old data
2540 : * in the members SLRU area.
2541 : *
2542 : * The return value is true if emergency autovacuum is required and false
2543 : * otherwise.
2544 : */
2545 : static bool
2546 1866 : SetOffsetVacuumLimit(bool is_startup)
2547 : {
2548 : MultiXactId oldestMultiXactId;
2549 : MultiXactId nextMXact;
2550 1866 : MultiXactOffset oldestOffset = 0; /* placate compiler */
2551 : MultiXactOffset prevOldestOffset;
2552 : MultiXactOffset nextOffset;
2553 1866 : bool oldestOffsetKnown = false;
2554 : bool prevOldestOffsetKnown;
2555 1866 : MultiXactOffset offsetStopLimit = 0;
2556 : MultiXactOffset prevOffsetStopLimit;
2557 :
2558 : /*
2559 : * NB: Have to prevent concurrent truncation, we might otherwise try to
2560 : * lookup an oldestMulti that's concurrently getting truncated away.
2561 : */
2562 1866 : LWLockAcquire(MultiXactTruncationLock, LW_SHARED);
2563 :
2564 : /* Read relevant fields from shared memory. */
2565 1866 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2566 1866 : oldestMultiXactId = MultiXactState->oldestMultiXactId;
2567 1866 : nextMXact = MultiXactState->nextMXact;
2568 1866 : nextOffset = MultiXactState->nextOffset;
2569 1866 : prevOldestOffsetKnown = MultiXactState->oldestOffsetKnown;
2570 1866 : prevOldestOffset = MultiXactState->oldestOffset;
2571 1866 : prevOffsetStopLimit = MultiXactState->offsetStopLimit;
2572 : Assert(MultiXactState->finishedStartup);
2573 1866 : LWLockRelease(MultiXactGenLock);
2574 :
2575 : /*
2576 : * Determine the offset of the oldest multixact. Normally, we can read
2577 : * the offset from the multixact itself, but there's an important special
2578 : * case: if there are no multixacts in existence at all, oldestMXact
2579 : * obviously can't point to one. It will instead point to the multixact
2580 : * ID that will be assigned the next time one is needed.
2581 : */
2582 1866 : if (oldestMultiXactId == nextMXact)
2583 : {
2584 : /*
2585 : * When the next multixact gets created, it will be stored at the next
2586 : * offset.
2587 : */
2588 1856 : oldestOffset = nextOffset;
2589 1856 : oldestOffsetKnown = true;
2590 : }
2591 : else
2592 : {
2593 : /*
2594 : * Figure out where the oldest existing multixact's offsets are
2595 : * stored. Due to bugs in early release of PostgreSQL 9.3.X and 9.4.X,
2596 : * the supposedly-earliest multixact might not really exist. We are
2597 : * careful not to fail in that case.
2598 : */
2599 10 : oldestOffsetKnown =
2600 : find_multixact_start(oldestMultiXactId, &oldestOffset);
2601 :
2602 10 : if (oldestOffsetKnown)
2603 10 : ereport(DEBUG1,
2604 : (errmsg("oldest MultiXactId member is at offset %u",
2605 : oldestOffset)));
2606 : else
2607 0 : ereport(LOG,
2608 : (errmsg("MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact %u does not exist on disk",
2609 : oldestMultiXactId)));
2610 : }
2611 :
2612 1866 : LWLockRelease(MultiXactTruncationLock);
2613 :
2614 : /*
2615 : * If we can, compute limits (and install them MultiXactState) to prevent
2616 : * overrun of old data in the members SLRU area. We can only do so if the
2617 : * oldest offset is known though.
2618 : */
2619 1866 : if (oldestOffsetKnown)
2620 : {
2621 : /* move back to start of the corresponding segment */
2622 1866 : offsetStopLimit = oldestOffset - (oldestOffset %
2623 : (MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT));
2624 :
2625 : /* always leave one segment before the wraparound point */
2626 1866 : offsetStopLimit -= (MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT);
2627 :
2628 1866 : if (!prevOldestOffsetKnown && !is_startup)
2629 0 : ereport(LOG,
2630 : (errmsg("MultiXact member wraparound protections are now enabled")));
2631 :
2632 1866 : ereport(DEBUG1,
2633 : (errmsg("MultiXact member stop limit is now %u based on MultiXact %u",
2634 : offsetStopLimit, oldestMultiXactId)));
2635 : }
2636 0 : else if (prevOldestOffsetKnown)
2637 : {
2638 : /*
2639 : * If we failed to get the oldest offset this time, but we have a
2640 : * value from a previous pass through this function, use the old
2641 : * values rather than automatically forcing an emergency autovacuum
2642 : * cycle again.
2643 : */
2644 0 : oldestOffset = prevOldestOffset;
2645 0 : oldestOffsetKnown = true;
2646 0 : offsetStopLimit = prevOffsetStopLimit;
2647 : }
2648 :
2649 : /* Install the computed values */
2650 1866 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2651 1866 : MultiXactState->oldestOffset = oldestOffset;
2652 1866 : MultiXactState->oldestOffsetKnown = oldestOffsetKnown;
2653 1866 : MultiXactState->offsetStopLimit = offsetStopLimit;
2654 1866 : LWLockRelease(MultiXactGenLock);
2655 :
2656 : /*
2657 : * Do we need an emergency autovacuum? If we're not sure, assume yes.
2658 : */
2659 3732 : return !oldestOffsetKnown ||
2660 1866 : (nextOffset - oldestOffset > MULTIXACT_MEMBER_SAFE_THRESHOLD);
2661 : }
2662 :
2663 : /*
2664 : * Return whether adding "distance" to "start" would move past "boundary".
2665 : *
2666 : * We use this to determine whether the addition is "wrapping around" the
2667 : * boundary point, hence the name. The reason we don't want to use the regular
2668 : * 2^31-modulo arithmetic here is that we want to be able to use the whole of
2669 : * the 2^32-1 space here, allowing for more multixacts that would fit
2670 : * otherwise.
2671 : */
2672 : static bool
2673 988 : MultiXactOffsetWouldWrap(MultiXactOffset boundary, MultiXactOffset start,
2674 : uint32 distance)
2675 : {
2676 : MultiXactOffset finish;
2677 :
2678 : /*
2679 : * Note that offset number 0 is not used (see GetMultiXactIdMembers), so
2680 : * if the addition wraps around the UINT_MAX boundary, skip that value.
2681 : */
2682 988 : finish = start + distance;
2683 988 : if (finish < start)
2684 0 : finish++;
2685 :
2686 : /*-----------------------------------------------------------------------
2687 : * When the boundary is numerically greater than the starting point, any
2688 : * value numerically between the two is not wrapped:
2689 : *
2690 : * <----S----B---->
2691 : * [---) = F wrapped past B (and UINT_MAX)
2692 : * [---) = F not wrapped
2693 : * [----] = F wrapped past B
2694 : *
2695 : * When the boundary is numerically less than the starting point (i.e. the
2696 : * UINT_MAX wraparound occurs somewhere in between) then all values in
2697 : * between are wrapped:
2698 : *
2699 : * <----B----S---->
2700 : * [---) = F not wrapped past B (but wrapped past UINT_MAX)
2701 : * [---) = F wrapped past B (and UINT_MAX)
2702 : * [----] = F not wrapped
2703 : *-----------------------------------------------------------------------
2704 : */
2705 988 : if (start < boundary)
2706 988 : return finish >= boundary || finish < start;
2707 : else
2708 0 : return finish >= boundary && finish < start;
2709 : }
2710 :
2711 : /*
2712 : * Find the starting offset of the given MultiXactId.
2713 : *
2714 : * Returns false if the file containing the multi does not exist on disk.
2715 : * Otherwise, returns true and sets *result to the starting member offset.
2716 : *
2717 : * This function does not prevent concurrent truncation, so if that's
2718 : * required, the caller has to protect against that.
2719 : */
2720 : static bool
2721 10 : find_multixact_start(MultiXactId multi, MultiXactOffset *result)
2722 : {
2723 : MultiXactOffset offset;
2724 : int pageno;
2725 : int entryno;
2726 : int slotno;
2727 : MultiXactOffset *offptr;
2728 :
2729 : Assert(MultiXactState->finishedStartup);
2730 :
2731 10 : pageno = MultiXactIdToOffsetPage(multi);
2732 10 : entryno = MultiXactIdToOffsetEntry(multi);
2733 :
2734 : /*
2735 : * Flush out dirty data, so PhysicalPageExists can work correctly.
2736 : * SimpleLruFlush() is a pretty big hammer for that. Alternatively we
2737 : * could add an in-memory version of page exists, but find_multixact_start
2738 : * is called infrequently, and it doesn't seem bad to flush buffers to
2739 : * disk before truncation.
2740 : */
2741 10 : SimpleLruFlush(MultiXactOffsetCtl, true);
2742 10 : SimpleLruFlush(MultiXactMemberCtl, true);
2743 :
2744 10 : if (!SimpleLruDoesPhysicalPageExist(MultiXactOffsetCtl, pageno))
2745 0 : return false;
2746 :
2747 : /* lock is acquired by SimpleLruReadPage_ReadOnly */
2748 10 : slotno = SimpleLruReadPage_ReadOnly(MultiXactOffsetCtl, pageno, multi);
2749 10 : offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
2750 10 : offptr += entryno;
2751 10 : offset = *offptr;
2752 10 : LWLockRelease(MultiXactOffsetControlLock);
2753 :
2754 10 : *result = offset;
2755 10 : return true;
2756 : }
2757 :
2758 : /*
2759 : * Determine how many multixacts, and how many multixact members, currently
2760 : * exist. Return false if unable to determine.
2761 : */
2762 : static bool
2763 40502 : ReadMultiXactCounts(uint32 *multixacts, MultiXactOffset *members)
2764 : {
2765 : MultiXactOffset nextOffset;
2766 : MultiXactOffset oldestOffset;
2767 : MultiXactId oldestMultiXactId;
2768 : MultiXactId nextMultiXactId;
2769 : bool oldestOffsetKnown;
2770 :
2771 40502 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2772 40502 : nextOffset = MultiXactState->nextOffset;
2773 40502 : oldestMultiXactId = MultiXactState->oldestMultiXactId;
2774 40502 : nextMultiXactId = MultiXactState->nextMXact;
2775 40502 : oldestOffset = MultiXactState->oldestOffset;
2776 40502 : oldestOffsetKnown = MultiXactState->oldestOffsetKnown;
2777 40502 : LWLockRelease(MultiXactGenLock);
2778 :
2779 40502 : if (!oldestOffsetKnown)
2780 0 : return false;
2781 :
2782 40502 : *members = nextOffset - oldestOffset;
2783 40502 : *multixacts = nextMultiXactId - oldestMultiXactId;
2784 40502 : return true;
2785 : }
2786 :
2787 : /*
2788 : * Multixact members can be removed once the multixacts that refer to them
2789 : * are older than every datminmxid. autovacuum_multixact_freeze_max_age and
2790 : * vacuum_multixact_freeze_table_age work together to make sure we never have
2791 : * too many multixacts; we hope that, at least under normal circumstances,
2792 : * this will also be sufficient to keep us from using too many offsets.
2793 : * However, if the average multixact has many members, we might exhaust the
2794 : * members space while still using few enough members that these limits fail
2795 : * to trigger full table scans for relminmxid advancement. At that point,
2796 : * we'd have no choice but to start failing multixact-creating operations
2797 : * with an error.
2798 : *
2799 : * To prevent that, if more than a threshold portion of the members space is
2800 : * used, we effectively reduce autovacuum_multixact_freeze_max_age and
2801 : * to a value just less than the number of multixacts in use. We hope that
2802 : * this will quickly trigger autovacuuming on the table or tables with the
2803 : * oldest relminmxid, thus allowing datminmxid values to advance and removing
2804 : * some members.
2805 : *
2806 : * As the fraction of the member space currently in use grows, we become
2807 : * more aggressive in clamping this value. That not only causes autovacuum
2808 : * to ramp up, but also makes any manual vacuums the user issues more
2809 : * aggressive. This happens because vacuum_set_xid_limits() clamps the
2810 : * freeze table and the minimum freeze age based on the effective
2811 : * autovacuum_multixact_freeze_max_age this function returns. In the worst
2812 : * case, we'll claim the freeze_max_age to zero, and every vacuum of any
2813 : * table will try to freeze every multixact.
2814 : *
2815 : * It's possible that these thresholds should be user-tunable, but for now
2816 : * we keep it simple.
2817 : */
2818 : int
2819 40502 : MultiXactMemberFreezeThreshold(void)
2820 : {
2821 : MultiXactOffset members;
2822 : uint32 multixacts;
2823 : uint32 victim_multixacts;
2824 : double fraction;
2825 :
2826 : /* If we can't determine member space utilization, assume the worst. */
2827 40502 : if (!ReadMultiXactCounts(&multixacts, &members))
2828 0 : return 0;
2829 :
2830 : /* If member space utilization is low, no special action is required. */
2831 40502 : if (members <= MULTIXACT_MEMBER_SAFE_THRESHOLD)
2832 40502 : return autovacuum_multixact_freeze_max_age;
2833 :
2834 : /*
2835 : * Compute a target for relminmxid advancement. The number of multixacts
2836 : * we try to eliminate from the system is based on how far we are past
2837 : * MULTIXACT_MEMBER_SAFE_THRESHOLD.
2838 : */
2839 0 : fraction = (double) (members - MULTIXACT_MEMBER_SAFE_THRESHOLD) /
2840 : (MULTIXACT_MEMBER_DANGER_THRESHOLD - MULTIXACT_MEMBER_SAFE_THRESHOLD);
2841 0 : victim_multixacts = multixacts * fraction;
2842 :
2843 : /* fraction could be > 1.0, but lowest possible freeze age is zero */
2844 0 : if (victim_multixacts > multixacts)
2845 0 : return 0;
2846 0 : return multixacts - victim_multixacts;
2847 : }
2848 :
2849 : typedef struct mxtruncinfo
2850 : {
2851 : int earliestExistingPage;
2852 : } mxtruncinfo;
2853 :
2854 : /*
2855 : * SlruScanDirectory callback
2856 : * This callback determines the earliest existing page number.
2857 : */
2858 : static bool
2859 0 : SlruScanDirCbFindEarliest(SlruCtl ctl, char *filename, int segpage, void *data)
2860 : {
2861 0 : mxtruncinfo *trunc = (mxtruncinfo *) data;
2862 :
2863 0 : if (trunc->earliestExistingPage == -1 ||
2864 0 : ctl->PagePrecedes(segpage, trunc->earliestExistingPage))
2865 : {
2866 0 : trunc->earliestExistingPage = segpage;
2867 : }
2868 :
2869 0 : return false; /* keep going */
2870 : }
2871 :
2872 :
2873 : /*
2874 : * Delete members segments [oldest, newOldest)
2875 : *
2876 : * The members SLRU can, in contrast to the offsets one, be filled to almost
2877 : * the full range at once. This means SimpleLruTruncate() can't trivially be
2878 : * used - instead the to-be-deleted range is computed using the offsets
2879 : * SLRU. C.f. TruncateMultiXact().
2880 : */
2881 : static void
2882 0 : PerformMembersTruncation(MultiXactOffset oldestOffset, MultiXactOffset newOldestOffset)
2883 : {
2884 0 : const int maxsegment = MXOffsetToMemberSegment(MaxMultiXactOffset);
2885 0 : int startsegment = MXOffsetToMemberSegment(oldestOffset);
2886 0 : int endsegment = MXOffsetToMemberSegment(newOldestOffset);
2887 0 : int segment = startsegment;
2888 :
2889 : /*
2890 : * Delete all the segments but the last one. The last segment can still
2891 : * contain, possibly partially, valid data.
2892 : */
2893 0 : while (segment != endsegment)
2894 : {
2895 0 : elog(DEBUG2, "truncating multixact members segment %x", segment);
2896 0 : SlruDeleteSegment(MultiXactMemberCtl, segment);
2897 :
2898 : /* move to next segment, handling wraparound correctly */
2899 0 : if (segment == maxsegment)
2900 0 : segment = 0;
2901 : else
2902 0 : segment += 1;
2903 : }
2904 0 : }
2905 :
2906 : /*
2907 : * Delete offsets segments [oldest, newOldest)
2908 : */
2909 : static void
2910 0 : PerformOffsetsTruncation(MultiXactId oldestMulti, MultiXactId newOldestMulti)
2911 : {
2912 : /*
2913 : * We step back one multixact to avoid passing a cutoff page that hasn't
2914 : * been created yet in the rare case that oldestMulti would be the first
2915 : * item on a page and oldestMulti == nextMulti. In that case, if we
2916 : * didn't subtract one, we'd trigger SimpleLruTruncate's wraparound
2917 : * detection.
2918 : */
2919 0 : SimpleLruTruncate(MultiXactOffsetCtl,
2920 0 : MultiXactIdToOffsetPage(PreviousMultiXactId(newOldestMulti)));
2921 0 : }
2922 :
2923 : /*
2924 : * Remove all MultiXactOffset and MultiXactMember segments before the oldest
2925 : * ones still of interest.
2926 : *
2927 : * This is only called on a primary as part of vacuum (via
2928 : * vac_truncate_clog()). During recovery truncation is done by replaying
2929 : * truncation WAL records logged here.
2930 : *
2931 : * newOldestMulti is the oldest currently required multixact, newOldestMultiDB
2932 : * is one of the databases preventing newOldestMulti from increasing.
2933 : */
2934 : void
2935 696 : TruncateMultiXact(MultiXactId newOldestMulti, Oid newOldestMultiDB)
2936 : {
2937 : MultiXactId oldestMulti;
2938 : MultiXactId nextMulti;
2939 : MultiXactOffset newOldestOffset;
2940 : MultiXactOffset oldestOffset;
2941 : MultiXactOffset nextOffset;
2942 : mxtruncinfo trunc;
2943 : MultiXactId earliest;
2944 :
2945 : Assert(!RecoveryInProgress());
2946 : Assert(MultiXactState->finishedStartup);
2947 :
2948 : /*
2949 : * We can only allow one truncation to happen at once. Otherwise parts of
2950 : * members might vanish while we're doing lookups or similar. There's no
2951 : * need to have an interlock with creating new multis or such, since those
2952 : * are constrained by the limits (which only grow, never shrink).
2953 : */
2954 696 : LWLockAcquire(MultiXactTruncationLock, LW_EXCLUSIVE);
2955 :
2956 696 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2957 696 : nextMulti = MultiXactState->nextMXact;
2958 696 : nextOffset = MultiXactState->nextOffset;
2959 696 : oldestMulti = MultiXactState->oldestMultiXactId;
2960 696 : LWLockRelease(MultiXactGenLock);
2961 : Assert(MultiXactIdIsValid(oldestMulti));
2962 :
2963 : /*
2964 : * Make sure to only attempt truncation if there's values to truncate
2965 : * away. In normal processing values shouldn't go backwards, but there's
2966 : * some corner cases (due to bugs) where that's possible.
2967 : */
2968 696 : if (MultiXactIdPrecedesOrEquals(newOldestMulti, oldestMulti))
2969 : {
2970 696 : LWLockRelease(MultiXactTruncationLock);
2971 696 : return;
2972 : }
2973 :
2974 : /*
2975 : * Note we can't just plow ahead with the truncation; it's possible that
2976 : * there are no segments to truncate, which is a problem because we are
2977 : * going to attempt to read the offsets page to determine where to
2978 : * truncate the members SLRU. So we first scan the directory to determine
2979 : * the earliest offsets page number that we can read without error.
2980 : *
2981 : * NB: It's also possible that the page that oldestMulti is on has already
2982 : * been truncated away, and we crashed before updating oldestMulti.
2983 : */
2984 0 : trunc.earliestExistingPage = -1;
2985 0 : SlruScanDirectory(MultiXactOffsetCtl, SlruScanDirCbFindEarliest, &trunc);
2986 0 : earliest = trunc.earliestExistingPage * MULTIXACT_OFFSETS_PER_PAGE;
2987 0 : if (earliest < FirstMultiXactId)
2988 0 : earliest = FirstMultiXactId;
2989 :
2990 : /* If there's nothing to remove, we can bail out early. */
2991 0 : if (MultiXactIdPrecedes(oldestMulti, earliest))
2992 : {
2993 0 : LWLockRelease(MultiXactTruncationLock);
2994 0 : return;
2995 : }
2996 :
2997 : /*
2998 : * First, compute the safe truncation point for MultiXactMember. This is
2999 : * the starting offset of the oldest multixact.
3000 : *
3001 : * Hopefully, find_multixact_start will always work here, because we've
3002 : * already checked that it doesn't precede the earliest MultiXact on disk.
3003 : * But if it fails, don't truncate anything, and log a message.
3004 : */
3005 0 : if (oldestMulti == nextMulti)
3006 : {
3007 : /* there are NO MultiXacts */
3008 0 : oldestOffset = nextOffset;
3009 : }
3010 0 : else if (!find_multixact_start(oldestMulti, &oldestOffset))
3011 : {
3012 0 : ereport(LOG,
3013 : (errmsg("oldest MultiXact %u not found, earliest MultiXact %u, skipping truncation",
3014 : oldestMulti, earliest)));
3015 0 : LWLockRelease(MultiXactTruncationLock);
3016 0 : return;
3017 : }
3018 :
3019 : /*
3020 : * Secondly compute up to where to truncate. Lookup the corresponding
3021 : * member offset for newOldestMulti for that.
3022 : */
3023 0 : if (newOldestMulti == nextMulti)
3024 : {
3025 : /* there are NO MultiXacts */
3026 0 : newOldestOffset = nextOffset;
3027 : }
3028 0 : else if (!find_multixact_start(newOldestMulti, &newOldestOffset))
3029 : {
3030 0 : ereport(LOG,
3031 : (errmsg("cannot truncate up to MultiXact %u because it does not exist on disk, skipping truncation",
3032 : newOldestMulti)));
3033 0 : LWLockRelease(MultiXactTruncationLock);
3034 0 : return;
3035 : }
3036 :
3037 0 : elog(DEBUG1, "performing multixact truncation: "
3038 : "offsets [%u, %u), offsets segments [%x, %x), "
3039 : "members [%u, %u), members segments [%x, %x)",
3040 : oldestMulti, newOldestMulti,
3041 : MultiXactIdToOffsetSegment(oldestMulti),
3042 : MultiXactIdToOffsetSegment(newOldestMulti),
3043 : oldestOffset, newOldestOffset,
3044 : MXOffsetToMemberSegment(oldestOffset),
3045 : MXOffsetToMemberSegment(newOldestOffset));
3046 :
3047 : /*
3048 : * Do truncation, and the WAL logging of the truncation, in a critical
3049 : * section. That way offsets/members cannot get out of sync anymore, i.e.
3050 : * once consistent the newOldestMulti will always exist in members, even
3051 : * if we crashed in the wrong moment.
3052 : */
3053 0 : START_CRIT_SECTION();
3054 :
3055 : /*
3056 : * Prevent checkpoints from being scheduled concurrently. This is critical
3057 : * because otherwise a truncation record might not be replayed after a
3058 : * crash/basebackup, even though the state of the data directory would
3059 : * require it.
3060 : */
3061 : Assert(!MyPgXact->delayChkpt);
3062 0 : MyPgXact->delayChkpt = true;
3063 :
3064 : /* WAL log truncation */
3065 0 : WriteMTruncateXlogRec(newOldestMultiDB,
3066 : oldestMulti, newOldestMulti,
3067 : oldestOffset, newOldestOffset);
3068 :
3069 : /*
3070 : * Update in-memory limits before performing the truncation, while inside
3071 : * the critical section: Have to do it before truncation, to prevent
3072 : * concurrent lookups of those values. Has to be inside the critical
3073 : * section as otherwise a future call to this function would error out,
3074 : * while looking up the oldest member in offsets, if our caller crashes
3075 : * before updating the limits.
3076 : */
3077 0 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
3078 0 : MultiXactState->oldestMultiXactId = newOldestMulti;
3079 0 : MultiXactState->oldestMultiXactDB = newOldestMultiDB;
3080 0 : LWLockRelease(MultiXactGenLock);
3081 :
3082 : /* First truncate members */
3083 0 : PerformMembersTruncation(oldestOffset, newOldestOffset);
3084 :
3085 : /* Then offsets */
3086 0 : PerformOffsetsTruncation(oldestMulti, newOldestMulti);
3087 :
3088 0 : MyPgXact->delayChkpt = false;
3089 :
3090 0 : END_CRIT_SECTION();
3091 0 : LWLockRelease(MultiXactTruncationLock);
3092 : }
3093 :
3094 : /*
3095 : * Decide which of two MultiXactOffset page numbers is "older" for truncation
3096 : * purposes.
3097 : *
3098 : * We need to use comparison of MultiXactId here in order to do the right
3099 : * thing with wraparound. However, if we are asked about page number zero, we
3100 : * don't want to hand InvalidMultiXactId to MultiXactIdPrecedes: it'll get
3101 : * weird. So, offset both multis by FirstMultiXactId to avoid that.
3102 : * (Actually, the current implementation doesn't do anything weird with
3103 : * InvalidMultiXactId, but there's no harm in leaving this code like this.)
3104 : */
3105 : static bool
3106 0 : MultiXactOffsetPagePrecedes(int page1, int page2)
3107 : {
3108 : MultiXactId multi1;
3109 : MultiXactId multi2;
3110 :
3111 0 : multi1 = ((MultiXactId) page1) * MULTIXACT_OFFSETS_PER_PAGE;
3112 0 : multi1 += FirstMultiXactId;
3113 0 : multi2 = ((MultiXactId) page2) * MULTIXACT_OFFSETS_PER_PAGE;
3114 0 : multi2 += FirstMultiXactId;
3115 :
3116 0 : return MultiXactIdPrecedes(multi1, multi2);
3117 : }
3118 :
3119 : /*
3120 : * Decide which of two MultiXactMember page numbers is "older" for truncation
3121 : * purposes. There is no "invalid offset number" so use the numbers verbatim.
3122 : */
3123 : static bool
3124 0 : MultiXactMemberPagePrecedes(int page1, int page2)
3125 : {
3126 : MultiXactOffset offset1;
3127 : MultiXactOffset offset2;
3128 :
3129 0 : offset1 = ((MultiXactOffset) page1) * MULTIXACT_MEMBERS_PER_PAGE;
3130 0 : offset2 = ((MultiXactOffset) page2) * MULTIXACT_MEMBERS_PER_PAGE;
3131 :
3132 0 : return MultiXactOffsetPrecedes(offset1, offset2);
3133 : }
3134 :
3135 : /*
3136 : * Decide which of two MultiXactIds is earlier.
3137 : *
3138 : * XXX do we need to do something special for InvalidMultiXactId?
3139 : * (Doesn't look like it.)
3140 : */
3141 : bool
3142 974558 : MultiXactIdPrecedes(MultiXactId multi1, MultiXactId multi2)
3143 : {
3144 974558 : int32 diff = (int32) (multi1 - multi2);
3145 :
3146 974558 : return (diff < 0);
3147 : }
3148 :
3149 : /*
3150 : * MultiXactIdPrecedesOrEquals -- is multi1 logically <= multi2?
3151 : *
3152 : * XXX do we need to do something special for InvalidMultiXactId?
3153 : * (Doesn't look like it.)
3154 : */
3155 : bool
3156 40504 : MultiXactIdPrecedesOrEquals(MultiXactId multi1, MultiXactId multi2)
3157 : {
3158 40504 : int32 diff = (int32) (multi1 - multi2);
3159 :
3160 40504 : return (diff <= 0);
3161 : }
3162 :
3163 :
3164 : /*
3165 : * Decide which of two offsets is earlier.
3166 : */
3167 : static bool
3168 128 : MultiXactOffsetPrecedes(MultiXactOffset offset1, MultiXactOffset offset2)
3169 : {
3170 128 : int32 diff = (int32) (offset1 - offset2);
3171 :
3172 128 : return (diff < 0);
3173 : }
3174 :
3175 : /*
3176 : * Write an xlog record reflecting the zeroing of either a MEMBERs or
3177 : * OFFSETs page (info shows which)
3178 : */
3179 : static void
3180 24 : WriteMZeroPageXlogRec(int pageno, uint8 info)
3181 : {
3182 24 : XLogBeginInsert();
3183 24 : XLogRegisterData((char *) (&pageno), sizeof(int));
3184 24 : (void) XLogInsert(RM_MULTIXACT_ID, info);
3185 24 : }
3186 :
3187 : /*
3188 : * Write a TRUNCATE xlog record
3189 : *
3190 : * We must flush the xlog record to disk before returning --- see notes in
3191 : * TruncateCLOG().
3192 : */
3193 : static void
3194 0 : WriteMTruncateXlogRec(Oid oldestMultiDB,
3195 : MultiXactId startTruncOff, MultiXactId endTruncOff,
3196 : MultiXactOffset startTruncMemb, MultiXactOffset endTruncMemb)
3197 : {
3198 : XLogRecPtr recptr;
3199 : xl_multixact_truncate xlrec;
3200 :
3201 0 : xlrec.oldestMultiDB = oldestMultiDB;
3202 :
3203 0 : xlrec.startTruncOff = startTruncOff;
3204 0 : xlrec.endTruncOff = endTruncOff;
3205 :
3206 0 : xlrec.startTruncMemb = startTruncMemb;
3207 0 : xlrec.endTruncMemb = endTruncMemb;
3208 :
3209 0 : XLogBeginInsert();
3210 0 : XLogRegisterData((char *) (&xlrec), SizeOfMultiXactTruncate);
3211 0 : recptr = XLogInsert(RM_MULTIXACT_ID, XLOG_MULTIXACT_TRUNCATE_ID);
3212 0 : XLogFlush(recptr);
3213 0 : }
3214 :
3215 : /*
3216 : * MULTIXACT resource manager's routines
3217 : */
3218 : void
3219 0 : multixact_redo(XLogReaderState *record)
3220 : {
3221 0 : uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
3222 :
3223 : /* Backup blocks are not used in multixact records */
3224 : Assert(!XLogRecHasAnyBlockRefs(record));
3225 :
3226 0 : if (info == XLOG_MULTIXACT_ZERO_OFF_PAGE)
3227 : {
3228 : int pageno;
3229 : int slotno;
3230 :
3231 0 : memcpy(&pageno, XLogRecGetData(record), sizeof(int));
3232 :
3233 0 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
3234 :
3235 0 : slotno = ZeroMultiXactOffsetPage(pageno, false);
3236 0 : SimpleLruWritePage(MultiXactOffsetCtl, slotno);
3237 : Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
3238 :
3239 0 : LWLockRelease(MultiXactOffsetControlLock);
3240 : }
3241 0 : else if (info == XLOG_MULTIXACT_ZERO_MEM_PAGE)
3242 : {
3243 : int pageno;
3244 : int slotno;
3245 :
3246 0 : memcpy(&pageno, XLogRecGetData(record), sizeof(int));
3247 :
3248 0 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
3249 :
3250 0 : slotno = ZeroMultiXactMemberPage(pageno, false);
3251 0 : SimpleLruWritePage(MultiXactMemberCtl, slotno);
3252 : Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
3253 :
3254 0 : LWLockRelease(MultiXactMemberControlLock);
3255 : }
3256 0 : else if (info == XLOG_MULTIXACT_CREATE_ID)
3257 : {
3258 0 : xl_multixact_create *xlrec =
3259 : (xl_multixact_create *) XLogRecGetData(record);
3260 : TransactionId max_xid;
3261 : int i;
3262 :
3263 : /* Store the data back into the SLRU files */
3264 0 : RecordNewMultiXact(xlrec->mid, xlrec->moff, xlrec->nmembers,
3265 0 : xlrec->members);
3266 :
3267 : /* Make sure nextMXact/nextOffset are beyond what this record has */
3268 0 : MultiXactAdvanceNextMXact(xlrec->mid + 1,
3269 0 : xlrec->moff + xlrec->nmembers);
3270 :
3271 : /*
3272 : * Make sure nextFullXid is beyond any XID mentioned in the record.
3273 : * This should be unnecessary, since any XID found here ought to have
3274 : * other evidence in the XLOG, but let's be safe.
3275 : */
3276 0 : max_xid = XLogRecGetXid(record);
3277 0 : for (i = 0; i < xlrec->nmembers; i++)
3278 : {
3279 0 : if (TransactionIdPrecedes(max_xid, xlrec->members[i].xid))
3280 0 : max_xid = xlrec->members[i].xid;
3281 : }
3282 :
3283 0 : AdvanceNextFullTransactionIdPastXid(max_xid);
3284 : }
3285 0 : else if (info == XLOG_MULTIXACT_TRUNCATE_ID)
3286 : {
3287 : xl_multixact_truncate xlrec;
3288 : int pageno;
3289 :
3290 0 : memcpy(&xlrec, XLogRecGetData(record),
3291 : SizeOfMultiXactTruncate);
3292 :
3293 0 : elog(DEBUG1, "replaying multixact truncation: "
3294 : "offsets [%u, %u), offsets segments [%x, %x), "
3295 : "members [%u, %u), members segments [%x, %x)",
3296 : xlrec.startTruncOff, xlrec.endTruncOff,
3297 : MultiXactIdToOffsetSegment(xlrec.startTruncOff),
3298 : MultiXactIdToOffsetSegment(xlrec.endTruncOff),
3299 : xlrec.startTruncMemb, xlrec.endTruncMemb,
3300 : MXOffsetToMemberSegment(xlrec.startTruncMemb),
3301 : MXOffsetToMemberSegment(xlrec.endTruncMemb));
3302 :
3303 : /* should not be required, but more than cheap enough */
3304 0 : LWLockAcquire(MultiXactTruncationLock, LW_EXCLUSIVE);
3305 :
3306 : /*
3307 : * Advance the horizon values, so they're current at the end of
3308 : * recovery.
3309 : */
3310 0 : SetMultiXactIdLimit(xlrec.endTruncOff, xlrec.oldestMultiDB, false);
3311 :
3312 0 : PerformMembersTruncation(xlrec.startTruncMemb, xlrec.endTruncMemb);
3313 :
3314 : /*
3315 : * During XLOG replay, latest_page_number isn't necessarily set up
3316 : * yet; insert a suitable value to bypass the sanity test in
3317 : * SimpleLruTruncate.
3318 : */
3319 0 : pageno = MultiXactIdToOffsetPage(xlrec.endTruncOff);
3320 0 : MultiXactOffsetCtl->shared->latest_page_number = pageno;
3321 0 : PerformOffsetsTruncation(xlrec.startTruncOff, xlrec.endTruncOff);
3322 :
3323 0 : LWLockRelease(MultiXactTruncationLock);
3324 : }
3325 : else
3326 0 : elog(PANIC, "multixact_redo: unknown op code %u", info);
3327 0 : }
3328 :
3329 : Datum
3330 0 : pg_get_multixact_members(PG_FUNCTION_ARGS)
3331 : {
3332 : typedef struct
3333 : {
3334 : MultiXactMember *members;
3335 : int nmembers;
3336 : int iter;
3337 : } mxact;
3338 0 : MultiXactId mxid = PG_GETARG_UINT32(0);
3339 : mxact *multi;
3340 : FuncCallContext *funccxt;
3341 :
3342 0 : if (mxid < FirstMultiXactId)
3343 0 : ereport(ERROR,
3344 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
3345 : errmsg("invalid MultiXactId: %u", mxid)));
3346 :
3347 0 : if (SRF_IS_FIRSTCALL())
3348 : {
3349 : MemoryContext oldcxt;
3350 : TupleDesc tupdesc;
3351 :
3352 0 : funccxt = SRF_FIRSTCALL_INIT();
3353 0 : oldcxt = MemoryContextSwitchTo(funccxt->multi_call_memory_ctx);
3354 :
3355 0 : multi = palloc(sizeof(mxact));
3356 : /* no need to allow for old values here */
3357 0 : multi->nmembers = GetMultiXactIdMembers(mxid, &multi->members, false,
3358 : false);
3359 0 : multi->iter = 0;
3360 :
3361 0 : tupdesc = CreateTemplateTupleDesc(2);
3362 0 : TupleDescInitEntry(tupdesc, (AttrNumber) 1, "xid",
3363 : XIDOID, -1, 0);
3364 0 : TupleDescInitEntry(tupdesc, (AttrNumber) 2, "mode",
3365 : TEXTOID, -1, 0);
3366 :
3367 0 : funccxt->attinmeta = TupleDescGetAttInMetadata(tupdesc);
3368 0 : funccxt->user_fctx = multi;
3369 :
3370 0 : MemoryContextSwitchTo(oldcxt);
3371 : }
3372 :
3373 0 : funccxt = SRF_PERCALL_SETUP();
3374 0 : multi = (mxact *) funccxt->user_fctx;
3375 :
3376 0 : while (multi->iter < multi->nmembers)
3377 : {
3378 : HeapTuple tuple;
3379 : char *values[2];
3380 :
3381 0 : values[0] = psprintf("%u", multi->members[multi->iter].xid);
3382 0 : values[1] = mxstatus_to_string(multi->members[multi->iter].status);
3383 :
3384 0 : tuple = BuildTupleFromCStrings(funccxt->attinmeta, values);
3385 :
3386 0 : multi->iter++;
3387 0 : pfree(values[0]);
3388 0 : SRF_RETURN_NEXT(funccxt, HeapTupleGetDatum(tuple));
3389 : }
3390 :
3391 0 : if (multi->nmembers > 0)
3392 0 : pfree(multi->members);
3393 0 : pfree(multi);
3394 :
3395 0 : SRF_RETURN_DONE(funccxt);
3396 : }
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