Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * clog.c
4 : * PostgreSQL transaction-commit-log manager
5 : *
6 : * This module replaces the old "pg_log" access code, which treated pg_log
7 : * essentially like a relation, in that it went through the regular buffer
8 : * manager. The problem with that was that there wasn't any good way to
9 : * recycle storage space for transactions so old that they'll never be
10 : * looked up again. Now we use specialized access code so that the commit
11 : * log can be broken into relatively small, independent segments.
12 : *
13 : * XLOG interactions: this module generates an XLOG record whenever a new
14 : * CLOG page is initialized to zeroes. Other writes of CLOG come from
15 : * recording of transaction commit or abort in xact.c, which generates its
16 : * own XLOG records for these events and will re-perform the status update
17 : * on redo; so we need make no additional XLOG entry here. For synchronous
18 : * transaction commits, the XLOG is guaranteed flushed through the XLOG commit
19 : * record before we are called to log a commit, so the WAL rule "write xlog
20 : * before data" is satisfied automatically. However, for async commits we
21 : * must track the latest LSN affecting each CLOG page, so that we can flush
22 : * XLOG that far and satisfy the WAL rule. We don't have to worry about this
23 : * for aborts (whether sync or async), since the post-crash assumption would
24 : * be that such transactions failed anyway.
25 : *
26 : * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
27 : * Portions Copyright (c) 1994, Regents of the University of California
28 : *
29 : * src/backend/access/transam/clog.c
30 : *
31 : *-------------------------------------------------------------------------
32 : */
33 : #include "postgres.h"
34 :
35 : #include "access/clog.h"
36 : #include "access/slru.h"
37 : #include "access/transam.h"
38 : #include "access/xlog.h"
39 : #include "access/xloginsert.h"
40 : #include "access/xlogutils.h"
41 : #include "miscadmin.h"
42 : #include "pg_trace.h"
43 : #include "pgstat.h"
44 : #include "storage/proc.h"
45 :
46 : /*
47 : * Defines for CLOG page sizes. A page is the same BLCKSZ as is used
48 : * everywhere else in Postgres.
49 : *
50 : * Note: because TransactionIds are 32 bits and wrap around at 0xFFFFFFFF,
51 : * CLOG page numbering also wraps around at 0xFFFFFFFF/CLOG_XACTS_PER_PAGE,
52 : * and CLOG segment numbering at
53 : * 0xFFFFFFFF/CLOG_XACTS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need take no
54 : * explicit notice of that fact in this module, except when comparing segment
55 : * and page numbers in TruncateCLOG (see CLOGPagePrecedes).
56 : */
57 :
58 : /* We need two bits per xact, so four xacts fit in a byte */
59 : #define CLOG_BITS_PER_XACT 2
60 : #define CLOG_XACTS_PER_BYTE 4
61 : #define CLOG_XACTS_PER_PAGE (BLCKSZ * CLOG_XACTS_PER_BYTE)
62 : #define CLOG_XACT_BITMASK ((1 << CLOG_BITS_PER_XACT) - 1)
63 :
64 : #define TransactionIdToPage(xid) ((xid) / (TransactionId) CLOG_XACTS_PER_PAGE)
65 : #define TransactionIdToPgIndex(xid) ((xid) % (TransactionId) CLOG_XACTS_PER_PAGE)
66 : #define TransactionIdToByte(xid) (TransactionIdToPgIndex(xid) / CLOG_XACTS_PER_BYTE)
67 : #define TransactionIdToBIndex(xid) ((xid) % (TransactionId) CLOG_XACTS_PER_BYTE)
68 :
69 : /* We store the latest async LSN for each group of transactions */
70 : #define CLOG_XACTS_PER_LSN_GROUP 32 /* keep this a power of 2 */
71 : #define CLOG_LSNS_PER_PAGE (CLOG_XACTS_PER_PAGE / CLOG_XACTS_PER_LSN_GROUP)
72 :
73 : #define GetLSNIndex(slotno, xid) ((slotno) * CLOG_LSNS_PER_PAGE + \
74 : ((xid) % (TransactionId) CLOG_XACTS_PER_PAGE) / CLOG_XACTS_PER_LSN_GROUP)
75 :
76 : /*
77 : * The number of subtransactions below which we consider to apply clog group
78 : * update optimization. Testing reveals that the number higher than this can
79 : * hurt performance.
80 : */
81 : #define THRESHOLD_SUBTRANS_CLOG_OPT 5
82 :
83 : /*
84 : * Link to shared-memory data structures for CLOG control
85 : */
86 : static SlruCtlData ClogCtlData;
87 :
88 : #define ClogCtl (&ClogCtlData)
89 :
90 :
91 : static int ZeroCLOGPage(int pageno, bool writeXlog);
92 : static bool CLOGPagePrecedes(int page1, int page2);
93 : static void WriteZeroPageXlogRec(int pageno);
94 : static void WriteTruncateXlogRec(int pageno, TransactionId oldestXact,
95 : Oid oldestXactDb);
96 : static void TransactionIdSetPageStatus(TransactionId xid, int nsubxids,
97 : TransactionId *subxids, XidStatus status,
98 : XLogRecPtr lsn, int pageno,
99 : bool all_xact_same_page);
100 : static void TransactionIdSetStatusBit(TransactionId xid, XidStatus status,
101 : XLogRecPtr lsn, int slotno);
102 : static void set_status_by_pages(int nsubxids, TransactionId *subxids,
103 : XidStatus status, XLogRecPtr lsn);
104 : static bool TransactionGroupUpdateXidStatus(TransactionId xid,
105 : XidStatus status, XLogRecPtr lsn, int pageno);
106 : static void TransactionIdSetPageStatusInternal(TransactionId xid, int nsubxids,
107 : TransactionId *subxids, XidStatus status,
108 : XLogRecPtr lsn, int pageno);
109 :
110 :
111 : /*
112 : * TransactionIdSetTreeStatus
113 : *
114 : * Record the final state of transaction entries in the commit log for
115 : * a transaction and its subtransaction tree. Take care to ensure this is
116 : * efficient, and as atomic as possible.
117 : *
118 : * xid is a single xid to set status for. This will typically be
119 : * the top level transactionid for a top level commit or abort. It can
120 : * also be a subtransaction when we record transaction aborts.
121 : *
122 : * subxids is an array of xids of length nsubxids, representing subtransactions
123 : * in the tree of xid. In various cases nsubxids may be zero.
124 : *
125 : * lsn must be the WAL location of the commit record when recording an async
126 : * commit. For a synchronous commit it can be InvalidXLogRecPtr, since the
127 : * caller guarantees the commit record is already flushed in that case. It
128 : * should be InvalidXLogRecPtr for abort cases, too.
129 : *
130 : * In the commit case, atomicity is limited by whether all the subxids are in
131 : * the same CLOG page as xid. If they all are, then the lock will be grabbed
132 : * only once, and the status will be set to committed directly. Otherwise
133 : * we must
134 : * 1. set sub-committed all subxids that are not on the same page as the
135 : * main xid
136 : * 2. atomically set committed the main xid and the subxids on the same page
137 : * 3. go over the first bunch again and set them committed
138 : * Note that as far as concurrent checkers are concerned, main transaction
139 : * commit as a whole is still atomic.
140 : *
141 : * Example:
142 : * TransactionId t commits and has subxids t1, t2, t3, t4
143 : * t is on page p1, t1 is also on p1, t2 and t3 are on p2, t4 is on p3
144 : * 1. update pages2-3:
145 : * page2: set t2,t3 as sub-committed
146 : * page3: set t4 as sub-committed
147 : * 2. update page1:
148 : * set t1 as sub-committed,
149 : * then set t as committed,
150 : then set t1 as committed
151 : * 3. update pages2-3:
152 : * page2: set t2,t3 as committed
153 : * page3: set t4 as committed
154 : *
155 : * NB: this is a low-level routine and is NOT the preferred entry point
156 : * for most uses; functions in transam.c are the intended callers.
157 : *
158 : * XXX Think about issuing POSIX_FADV_WILLNEED on pages that we will need,
159 : * but aren't yet in cache, as well as hinting pages not to fall out of
160 : * cache yet.
161 : */
162 : void
163 256178 : TransactionIdSetTreeStatus(TransactionId xid, int nsubxids,
164 : TransactionId *subxids, XidStatus status, XLogRecPtr lsn)
165 : {
166 256178 : int pageno = TransactionIdToPage(xid); /* get page of parent */
167 : int i;
168 :
169 : Assert(status == TRANSACTION_STATUS_COMMITTED ||
170 : status == TRANSACTION_STATUS_ABORTED);
171 :
172 : /*
173 : * See how many subxids, if any, are on the same page as the parent, if
174 : * any.
175 : */
176 260402 : for (i = 0; i < nsubxids; i++)
177 : {
178 4224 : if (TransactionIdToPage(subxids[i]) != pageno)
179 0 : break;
180 : }
181 :
182 : /*
183 : * Do all items fit on a single page?
184 : */
185 256178 : if (i == nsubxids)
186 : {
187 : /*
188 : * Set the parent and all subtransactions in a single call
189 : */
190 256178 : TransactionIdSetPageStatus(xid, nsubxids, subxids, status, lsn,
191 : pageno, true);
192 : }
193 : else
194 : {
195 0 : int nsubxids_on_first_page = i;
196 :
197 : /*
198 : * If this is a commit then we care about doing this correctly (i.e.
199 : * using the subcommitted intermediate status). By here, we know
200 : * we're updating more than one page of clog, so we must mark entries
201 : * that are *not* on the first page so that they show as subcommitted
202 : * before we then return to update the status to fully committed.
203 : *
204 : * To avoid touching the first page twice, skip marking subcommitted
205 : * for the subxids on that first page.
206 : */
207 0 : if (status == TRANSACTION_STATUS_COMMITTED)
208 0 : set_status_by_pages(nsubxids - nsubxids_on_first_page,
209 0 : subxids + nsubxids_on_first_page,
210 : TRANSACTION_STATUS_SUB_COMMITTED, lsn);
211 :
212 : /*
213 : * Now set the parent and subtransactions on same page as the parent,
214 : * if any
215 : */
216 0 : pageno = TransactionIdToPage(xid);
217 0 : TransactionIdSetPageStatus(xid, nsubxids_on_first_page, subxids, status,
218 : lsn, pageno, false);
219 :
220 : /*
221 : * Now work through the rest of the subxids one clog page at a time,
222 : * starting from the second page onwards, like we did above.
223 : */
224 0 : set_status_by_pages(nsubxids - nsubxids_on_first_page,
225 0 : subxids + nsubxids_on_first_page,
226 : status, lsn);
227 : }
228 256178 : }
229 :
230 : /*
231 : * Helper for TransactionIdSetTreeStatus: set the status for a bunch of
232 : * transactions, chunking in the separate CLOG pages involved. We never
233 : * pass the whole transaction tree to this function, only subtransactions
234 : * that are on different pages to the top level transaction id.
235 : */
236 : static void
237 0 : set_status_by_pages(int nsubxids, TransactionId *subxids,
238 : XidStatus status, XLogRecPtr lsn)
239 : {
240 0 : int pageno = TransactionIdToPage(subxids[0]);
241 0 : int offset = 0;
242 0 : int i = 0;
243 :
244 : Assert(nsubxids > 0); /* else the pageno fetch above is unsafe */
245 :
246 0 : while (i < nsubxids)
247 : {
248 0 : int num_on_page = 0;
249 : int nextpageno;
250 :
251 : do
252 : {
253 0 : nextpageno = TransactionIdToPage(subxids[i]);
254 0 : if (nextpageno != pageno)
255 0 : break;
256 0 : num_on_page++;
257 0 : i++;
258 0 : } while (i < nsubxids);
259 :
260 0 : TransactionIdSetPageStatus(InvalidTransactionId,
261 0 : num_on_page, subxids + offset,
262 : status, lsn, pageno, false);
263 0 : offset = i;
264 0 : pageno = nextpageno;
265 : }
266 0 : }
267 :
268 : /*
269 : * Record the final state of transaction entries in the commit log for all
270 : * entries on a single page. Atomic only on this page.
271 : */
272 : static void
273 256178 : TransactionIdSetPageStatus(TransactionId xid, int nsubxids,
274 : TransactionId *subxids, XidStatus status,
275 : XLogRecPtr lsn, int pageno,
276 : bool all_xact_same_page)
277 : {
278 : /* Can't use group update when PGPROC overflows. */
279 : StaticAssertStmt(THRESHOLD_SUBTRANS_CLOG_OPT <= PGPROC_MAX_CACHED_SUBXIDS,
280 : "group clog threshold less than PGPROC cached subxids");
281 :
282 : /*
283 : * When there is contention on CLogControlLock, we try to group multiple
284 : * updates; a single leader process will perform transaction status
285 : * updates for multiple backends so that the number of times
286 : * CLogControlLock needs to be acquired is reduced.
287 : *
288 : * For this optimization to be safe, the XID in MyPgXact and the subxids
289 : * in MyProc must be the same as the ones for which we're setting the
290 : * status. Check that this is the case.
291 : *
292 : * For this optimization to be efficient, we shouldn't have too many
293 : * sub-XIDs and all of the XIDs for which we're adjusting clog should be
294 : * on the same page. Check those conditions, too.
295 : */
296 256178 : if (all_xact_same_page && xid == MyPgXact->xid &&
297 251530 : nsubxids <= THRESHOLD_SUBTRANS_CLOG_OPT &&
298 503060 : nsubxids == MyPgXact->nxids &&
299 251530 : memcmp(subxids, MyProc->subxids.xids,
300 : nsubxids * sizeof(TransactionId)) == 0)
301 : {
302 : /*
303 : * We don't try to do group update optimization if a process has
304 : * overflowed the subxids array in its PGPROC, since in that case we
305 : * don't have a complete list of XIDs for it.
306 : */
307 : Assert(THRESHOLD_SUBTRANS_CLOG_OPT <= PGPROC_MAX_CACHED_SUBXIDS);
308 :
309 : /*
310 : * If we can immediately acquire CLogControlLock, we update the status
311 : * of our own XID and release the lock. If not, try use group XID
312 : * update. If that doesn't work out, fall back to waiting for the
313 : * lock to perform an update for this transaction only.
314 : */
315 251530 : if (LWLockConditionalAcquire(CLogControlLock, LW_EXCLUSIVE))
316 : {
317 : /* Got the lock without waiting! Do the update. */
318 251516 : TransactionIdSetPageStatusInternal(xid, nsubxids, subxids, status,
319 : lsn, pageno);
320 251516 : LWLockRelease(CLogControlLock);
321 251516 : return;
322 : }
323 14 : else if (TransactionGroupUpdateXidStatus(xid, status, lsn, pageno))
324 : {
325 : /* Group update mechanism has done the work. */
326 14 : return;
327 : }
328 :
329 : /* Fall through only if update isn't done yet. */
330 : }
331 :
332 : /* Group update not applicable, or couldn't accept this page number. */
333 4648 : LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
334 4648 : TransactionIdSetPageStatusInternal(xid, nsubxids, subxids, status,
335 : lsn, pageno);
336 4648 : LWLockRelease(CLogControlLock);
337 : }
338 :
339 : /*
340 : * Record the final state of transaction entry in the commit log
341 : *
342 : * We don't do any locking here; caller must handle that.
343 : */
344 : static void
345 256178 : TransactionIdSetPageStatusInternal(TransactionId xid, int nsubxids,
346 : TransactionId *subxids, XidStatus status,
347 : XLogRecPtr lsn, int pageno)
348 : {
349 : int slotno;
350 : int i;
351 :
352 : Assert(status == TRANSACTION_STATUS_COMMITTED ||
353 : status == TRANSACTION_STATUS_ABORTED ||
354 : (status == TRANSACTION_STATUS_SUB_COMMITTED && !TransactionIdIsValid(xid)));
355 : Assert(LWLockHeldByMeInMode(CLogControlLock, LW_EXCLUSIVE));
356 :
357 : /*
358 : * If we're doing an async commit (ie, lsn is valid), then we must wait
359 : * for any active write on the page slot to complete. Otherwise our
360 : * update could reach disk in that write, which will not do since we
361 : * mustn't let it reach disk until we've done the appropriate WAL flush.
362 : * But when lsn is invalid, it's OK to scribble on a page while it is
363 : * write-busy, since we don't care if the update reaches disk sooner than
364 : * we think.
365 : */
366 256178 : slotno = SimpleLruReadPage(ClogCtl, pageno, XLogRecPtrIsInvalid(lsn), xid);
367 :
368 : /*
369 : * Set the main transaction id, if any.
370 : *
371 : * If we update more than one xid on this page while it is being written
372 : * out, we might find that some of the bits go to disk and others don't.
373 : * If we are updating commits on the page with the top-level xid that
374 : * could break atomicity, so we subcommit the subxids first before we mark
375 : * the top-level commit.
376 : */
377 256178 : if (TransactionIdIsValid(xid))
378 : {
379 : /* Subtransactions first, if needed ... */
380 256178 : if (status == TRANSACTION_STATUS_COMMITTED)
381 : {
382 254230 : for (i = 0; i < nsubxids; i++)
383 : {
384 : Assert(ClogCtl->shared->page_number[slotno] == TransactionIdToPage(subxids[i]));
385 3634 : TransactionIdSetStatusBit(subxids[i],
386 : TRANSACTION_STATUS_SUB_COMMITTED,
387 : lsn, slotno);
388 : }
389 : }
390 :
391 : /* ... then the main transaction */
392 256178 : TransactionIdSetStatusBit(xid, status, lsn, slotno);
393 : }
394 :
395 : /* Set the subtransactions */
396 260402 : for (i = 0; i < nsubxids; i++)
397 : {
398 : Assert(ClogCtl->shared->page_number[slotno] == TransactionIdToPage(subxids[i]));
399 4224 : TransactionIdSetStatusBit(subxids[i], status, lsn, slotno);
400 : }
401 :
402 256178 : ClogCtl->shared->page_dirty[slotno] = true;
403 256178 : }
404 :
405 : /*
406 : * When we cannot immediately acquire CLogControlLock in exclusive mode at
407 : * commit time, add ourselves to a list of processes that need their XIDs
408 : * status update. The first process to add itself to the list will acquire
409 : * CLogControlLock in exclusive mode and set transaction status as required
410 : * on behalf of all group members. This avoids a great deal of contention
411 : * around CLogControlLock when many processes are trying to commit at once,
412 : * since the lock need not be repeatedly handed off from one committing
413 : * process to the next.
414 : *
415 : * Returns true when transaction status has been updated in clog; returns
416 : * false if we decided against applying the optimization because the page
417 : * number we need to update differs from those processes already waiting.
418 : */
419 : static bool
420 14 : TransactionGroupUpdateXidStatus(TransactionId xid, XidStatus status,
421 : XLogRecPtr lsn, int pageno)
422 : {
423 14 : volatile PROC_HDR *procglobal = ProcGlobal;
424 14 : PGPROC *proc = MyProc;
425 : uint32 nextidx;
426 : uint32 wakeidx;
427 :
428 : /* We should definitely have an XID whose status needs to be updated. */
429 : Assert(TransactionIdIsValid(xid));
430 :
431 : /*
432 : * Add ourselves to the list of processes needing a group XID status
433 : * update.
434 : */
435 14 : proc->clogGroupMember = true;
436 14 : proc->clogGroupMemberXid = xid;
437 14 : proc->clogGroupMemberXidStatus = status;
438 14 : proc->clogGroupMemberPage = pageno;
439 14 : proc->clogGroupMemberLsn = lsn;
440 :
441 14 : nextidx = pg_atomic_read_u32(&procglobal->clogGroupFirst);
442 :
443 : while (true)
444 : {
445 : /*
446 : * Add the proc to list, if the clog page where we need to update the
447 : * current transaction status is same as group leader's clog page.
448 : *
449 : * There is a race condition here, which is that after doing the below
450 : * check and before adding this proc's clog update to a group, the
451 : * group leader might have already finished the group update for this
452 : * page and becomes group leader of another group. This will lead to a
453 : * situation where a single group can have different clog page
454 : * updates. This isn't likely and will still work, just maybe a bit
455 : * less efficiently.
456 : */
457 14 : if (nextidx != INVALID_PGPROCNO &&
458 0 : ProcGlobal->allProcs[nextidx].clogGroupMemberPage != proc->clogGroupMemberPage)
459 : {
460 0 : proc->clogGroupMember = false;
461 0 : return false;
462 : }
463 :
464 14 : pg_atomic_write_u32(&proc->clogGroupNext, nextidx);
465 :
466 14 : if (pg_atomic_compare_exchange_u32(&procglobal->clogGroupFirst,
467 : &nextidx,
468 14 : (uint32) proc->pgprocno))
469 14 : break;
470 : }
471 :
472 : /*
473 : * If the list was not empty, the leader will update the status of our
474 : * XID. It is impossible to have followers without a leader because the
475 : * first process that has added itself to the list will always have
476 : * nextidx as INVALID_PGPROCNO.
477 : */
478 14 : if (nextidx != INVALID_PGPROCNO)
479 : {
480 0 : int extraWaits = 0;
481 :
482 : /* Sleep until the leader updates our XID status. */
483 0 : pgstat_report_wait_start(WAIT_EVENT_CLOG_GROUP_UPDATE);
484 : for (;;)
485 : {
486 : /* acts as a read barrier */
487 0 : PGSemaphoreLock(proc->sem);
488 0 : if (!proc->clogGroupMember)
489 0 : break;
490 0 : extraWaits++;
491 : }
492 0 : pgstat_report_wait_end();
493 :
494 : Assert(pg_atomic_read_u32(&proc->clogGroupNext) == INVALID_PGPROCNO);
495 :
496 : /* Fix semaphore count for any absorbed wakeups */
497 0 : while (extraWaits-- > 0)
498 0 : PGSemaphoreUnlock(proc->sem);
499 0 : return true;
500 : }
501 :
502 : /* We are the leader. Acquire the lock on behalf of everyone. */
503 14 : LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
504 :
505 : /*
506 : * Now that we've got the lock, clear the list of processes waiting for
507 : * group XID status update, saving a pointer to the head of the list.
508 : * Trying to pop elements one at a time could lead to an ABA problem.
509 : */
510 14 : nextidx = pg_atomic_exchange_u32(&procglobal->clogGroupFirst,
511 : INVALID_PGPROCNO);
512 :
513 : /* Remember head of list so we can perform wakeups after dropping lock. */
514 14 : wakeidx = nextidx;
515 :
516 : /* Walk the list and update the status of all XIDs. */
517 42 : while (nextidx != INVALID_PGPROCNO)
518 : {
519 14 : PGPROC *proc = &ProcGlobal->allProcs[nextidx];
520 14 : PGXACT *pgxact = &ProcGlobal->allPgXact[nextidx];
521 :
522 : /*
523 : * Overflowed transactions should not use group XID status update
524 : * mechanism.
525 : */
526 : Assert(!pgxact->overflowed);
527 :
528 28 : TransactionIdSetPageStatusInternal(proc->clogGroupMemberXid,
529 14 : pgxact->nxids,
530 14 : proc->subxids.xids,
531 : proc->clogGroupMemberXidStatus,
532 : proc->clogGroupMemberLsn,
533 : proc->clogGroupMemberPage);
534 :
535 : /* Move to next proc in list. */
536 14 : nextidx = pg_atomic_read_u32(&proc->clogGroupNext);
537 : }
538 :
539 : /* We're done with the lock now. */
540 14 : LWLockRelease(CLogControlLock);
541 :
542 : /*
543 : * Now that we've released the lock, go back and wake everybody up. We
544 : * don't do this under the lock so as to keep lock hold times to a
545 : * minimum.
546 : */
547 42 : while (wakeidx != INVALID_PGPROCNO)
548 : {
549 14 : PGPROC *proc = &ProcGlobal->allProcs[wakeidx];
550 :
551 14 : wakeidx = pg_atomic_read_u32(&proc->clogGroupNext);
552 14 : pg_atomic_write_u32(&proc->clogGroupNext, INVALID_PGPROCNO);
553 :
554 : /* ensure all previous writes are visible before follower continues. */
555 14 : pg_write_barrier();
556 :
557 14 : proc->clogGroupMember = false;
558 :
559 14 : if (proc != MyProc)
560 0 : PGSemaphoreUnlock(proc->sem);
561 : }
562 :
563 14 : return true;
564 : }
565 :
566 : /*
567 : * Sets the commit status of a single transaction.
568 : *
569 : * Must be called with CLogControlLock held
570 : */
571 : static void
572 264036 : TransactionIdSetStatusBit(TransactionId xid, XidStatus status, XLogRecPtr lsn, int slotno)
573 : {
574 264036 : int byteno = TransactionIdToByte(xid);
575 264036 : int bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
576 : char *byteptr;
577 : char byteval;
578 : char curval;
579 :
580 264036 : byteptr = ClogCtl->shared->page_buffer[slotno] + byteno;
581 264036 : curval = (*byteptr >> bshift) & CLOG_XACT_BITMASK;
582 :
583 : /*
584 : * When replaying transactions during recovery we still need to perform
585 : * the two phases of subcommit and then commit. However, some transactions
586 : * are already correctly marked, so we just treat those as a no-op which
587 : * allows us to keep the following Assert as restrictive as possible.
588 : */
589 264036 : if (InRecovery && status == TRANSACTION_STATUS_SUB_COMMITTED &&
590 : curval == TRANSACTION_STATUS_COMMITTED)
591 0 : return;
592 :
593 : /*
594 : * Current state change should be from 0 or subcommitted to target state
595 : * or we should already be there when replaying changes during recovery.
596 : */
597 : Assert(curval == 0 ||
598 : (curval == TRANSACTION_STATUS_SUB_COMMITTED &&
599 : status != TRANSACTION_STATUS_IN_PROGRESS) ||
600 : curval == status);
601 :
602 : /* note this assumes exclusive access to the clog page */
603 264036 : byteval = *byteptr;
604 264036 : byteval &= ~(((1 << CLOG_BITS_PER_XACT) - 1) << bshift);
605 264036 : byteval |= (status << bshift);
606 264036 : *byteptr = byteval;
607 :
608 : /*
609 : * Update the group LSN if the transaction completion LSN is higher.
610 : *
611 : * Note: lsn will be invalid when supplied during InRecovery processing,
612 : * so we don't need to do anything special to avoid LSN updates during
613 : * recovery. After recovery completes the next clog change will set the
614 : * LSN correctly.
615 : */
616 264036 : if (!XLogRecPtrIsInvalid(lsn))
617 : {
618 12618 : int lsnindex = GetLSNIndex(slotno, xid);
619 :
620 12618 : if (ClogCtl->shared->group_lsn[lsnindex] < lsn)
621 11526 : ClogCtl->shared->group_lsn[lsnindex] = lsn;
622 : }
623 : }
624 :
625 : /*
626 : * Interrogate the state of a transaction in the commit log.
627 : *
628 : * Aside from the actual commit status, this function returns (into *lsn)
629 : * an LSN that is late enough to be able to guarantee that if we flush up to
630 : * that LSN then we will have flushed the transaction's commit record to disk.
631 : * The result is not necessarily the exact LSN of the transaction's commit
632 : * record! For example, for long-past transactions (those whose clog pages
633 : * already migrated to disk), we'll return InvalidXLogRecPtr. Also, because
634 : * we group transactions on the same clog page to conserve storage, we might
635 : * return the LSN of a later transaction that falls into the same group.
636 : *
637 : * NB: this is a low-level routine and is NOT the preferred entry point
638 : * for most uses; TransactionLogFetch() in transam.c is the intended caller.
639 : */
640 : XidStatus
641 1067816 : TransactionIdGetStatus(TransactionId xid, XLogRecPtr *lsn)
642 : {
643 1067816 : int pageno = TransactionIdToPage(xid);
644 1067816 : int byteno = TransactionIdToByte(xid);
645 1067816 : int bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
646 : int slotno;
647 : int lsnindex;
648 : char *byteptr;
649 : XidStatus status;
650 :
651 : /* lock is acquired by SimpleLruReadPage_ReadOnly */
652 :
653 1067816 : slotno = SimpleLruReadPage_ReadOnly(ClogCtl, pageno, xid);
654 1067816 : byteptr = ClogCtl->shared->page_buffer[slotno] + byteno;
655 :
656 1067816 : status = (*byteptr >> bshift) & CLOG_XACT_BITMASK;
657 :
658 1067816 : lsnindex = GetLSNIndex(slotno, xid);
659 1067816 : *lsn = ClogCtl->shared->group_lsn[lsnindex];
660 :
661 1067816 : LWLockRelease(CLogControlLock);
662 :
663 1067816 : return status;
664 : }
665 :
666 : /*
667 : * Number of shared CLOG buffers.
668 : *
669 : * On larger multi-processor systems, it is possible to have many CLOG page
670 : * requests in flight at one time which could lead to disk access for CLOG
671 : * page if the required page is not found in memory. Testing revealed that we
672 : * can get the best performance by having 128 CLOG buffers, more than that it
673 : * doesn't improve performance.
674 : *
675 : * Unconditionally keeping the number of CLOG buffers to 128 did not seem like
676 : * a good idea, because it would increase the minimum amount of shared memory
677 : * required to start, which could be a problem for people running very small
678 : * configurations. The following formula seems to represent a reasonable
679 : * compromise: people with very low values for shared_buffers will get fewer
680 : * CLOG buffers as well, and everyone else will get 128.
681 : */
682 : Size
683 3784 : CLOGShmemBuffers(void)
684 : {
685 3784 : return Min(128, Max(4, NBuffers / 512));
686 : }
687 :
688 : /*
689 : * Initialization of shared memory for CLOG
690 : */
691 : Size
692 1894 : CLOGShmemSize(void)
693 : {
694 1894 : return SimpleLruShmemSize(CLOGShmemBuffers(), CLOG_LSNS_PER_PAGE);
695 : }
696 :
697 : void
698 1890 : CLOGShmemInit(void)
699 : {
700 1890 : ClogCtl->PagePrecedes = CLOGPagePrecedes;
701 1890 : SimpleLruInit(ClogCtl, "clog", CLOGShmemBuffers(), CLOG_LSNS_PER_PAGE,
702 1890 : CLogControlLock, "pg_xact", LWTRANCHE_CLOG_BUFFERS);
703 1890 : }
704 :
705 : /*
706 : * This func must be called ONCE on system install. It creates
707 : * the initial CLOG segment. (The CLOG directory is assumed to
708 : * have been created by initdb, and CLOGShmemInit must have been
709 : * called already.)
710 : */
711 : void
712 322 : BootStrapCLOG(void)
713 : {
714 : int slotno;
715 :
716 322 : LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
717 :
718 : /* Create and zero the first page of the commit log */
719 322 : slotno = ZeroCLOGPage(0, false);
720 :
721 : /* Make sure it's written out */
722 322 : SimpleLruWritePage(ClogCtl, slotno);
723 : Assert(!ClogCtl->shared->page_dirty[slotno]);
724 :
725 322 : LWLockRelease(CLogControlLock);
726 322 : }
727 :
728 : /*
729 : * Initialize (or reinitialize) a page of CLOG to zeroes.
730 : * If writeXlog is true, also emit an XLOG record saying we did this.
731 : *
732 : * The page is not actually written, just set up in shared memory.
733 : * The slot number of the new page is returned.
734 : *
735 : * Control lock must be held at entry, and will be held at exit.
736 : */
737 : static int
738 644 : ZeroCLOGPage(int pageno, bool writeXlog)
739 : {
740 : int slotno;
741 :
742 644 : slotno = SimpleLruZeroPage(ClogCtl, pageno);
743 :
744 644 : if (writeXlog)
745 322 : WriteZeroPageXlogRec(pageno);
746 :
747 644 : return slotno;
748 : }
749 :
750 : /*
751 : * This must be called ONCE during postmaster or standalone-backend startup,
752 : * after StartupXLOG has initialized ShmemVariableCache->nextFullXid.
753 : */
754 : void
755 1192 : StartupCLOG(void)
756 : {
757 1192 : TransactionId xid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
758 1192 : int pageno = TransactionIdToPage(xid);
759 :
760 1192 : LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
761 :
762 : /*
763 : * Initialize our idea of the latest page number.
764 : */
765 1192 : ClogCtl->shared->latest_page_number = pageno;
766 :
767 1192 : LWLockRelease(CLogControlLock);
768 1192 : }
769 :
770 : /*
771 : * This must be called ONCE at the end of startup/recovery.
772 : */
773 : void
774 1170 : TrimCLOG(void)
775 : {
776 1170 : TransactionId xid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
777 1170 : int pageno = TransactionIdToPage(xid);
778 :
779 1170 : LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
780 :
781 : /*
782 : * Re-Initialize our idea of the latest page number.
783 : */
784 1170 : ClogCtl->shared->latest_page_number = pageno;
785 :
786 : /*
787 : * Zero out the remainder of the current clog page. Under normal
788 : * circumstances it should be zeroes already, but it seems at least
789 : * theoretically possible that XLOG replay will have settled on a nextXID
790 : * value that is less than the last XID actually used and marked by the
791 : * previous database lifecycle (since subtransaction commit writes clog
792 : * but makes no WAL entry). Let's just be safe. (We need not worry about
793 : * pages beyond the current one, since those will be zeroed when first
794 : * used. For the same reason, there is no need to do anything when
795 : * nextFullXid is exactly at a page boundary; and it's likely that the
796 : * "current" page doesn't exist yet in that case.)
797 : */
798 1170 : if (TransactionIdToPgIndex(xid) != 0)
799 : {
800 1170 : int byteno = TransactionIdToByte(xid);
801 1170 : int bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
802 : int slotno;
803 : char *byteptr;
804 :
805 1170 : slotno = SimpleLruReadPage(ClogCtl, pageno, false, xid);
806 1170 : byteptr = ClogCtl->shared->page_buffer[slotno] + byteno;
807 :
808 : /* Zero so-far-unused positions in the current byte */
809 1170 : *byteptr &= (1 << bshift) - 1;
810 : /* Zero the rest of the page */
811 1170 : MemSet(byteptr + 1, 0, BLCKSZ - byteno - 1);
812 :
813 1170 : ClogCtl->shared->page_dirty[slotno] = true;
814 : }
815 :
816 1170 : LWLockRelease(CLogControlLock);
817 1170 : }
818 :
819 : /*
820 : * This must be called ONCE during postmaster or standalone-backend shutdown
821 : */
822 : void
823 1024 : ShutdownCLOG(void)
824 : {
825 : /* Flush dirty CLOG pages to disk */
826 : TRACE_POSTGRESQL_CLOG_CHECKPOINT_START(false);
827 1024 : SimpleLruFlush(ClogCtl, false);
828 :
829 : /*
830 : * fsync pg_xact to ensure that any files flushed previously are durably
831 : * on disk.
832 : */
833 1024 : fsync_fname("pg_xact", true);
834 :
835 : TRACE_POSTGRESQL_CLOG_CHECKPOINT_DONE(false);
836 1024 : }
837 :
838 : /*
839 : * Perform a checkpoint --- either during shutdown, or on-the-fly
840 : */
841 : void
842 2832 : CheckPointCLOG(void)
843 : {
844 : /* Flush dirty CLOG pages to disk */
845 : TRACE_POSTGRESQL_CLOG_CHECKPOINT_START(true);
846 2832 : SimpleLruFlush(ClogCtl, true);
847 :
848 : /*
849 : * fsync pg_xact to ensure that any files flushed previously are durably
850 : * on disk.
851 : */
852 2832 : fsync_fname("pg_xact", true);
853 :
854 : TRACE_POSTGRESQL_CLOG_CHECKPOINT_DONE(true);
855 2832 : }
856 :
857 :
858 : /*
859 : * Make sure that CLOG has room for a newly-allocated XID.
860 : *
861 : * NB: this is called while holding XidGenLock. We want it to be very fast
862 : * most of the time; even when it's not so fast, no actual I/O need happen
863 : * unless we're forced to write out a dirty clog or xlog page to make room
864 : * in shared memory.
865 : */
866 : void
867 255284 : ExtendCLOG(TransactionId newestXact)
868 : {
869 : int pageno;
870 :
871 : /*
872 : * No work except at first XID of a page. But beware: just after
873 : * wraparound, the first XID of page zero is FirstNormalTransactionId.
874 : */
875 255284 : if (TransactionIdToPgIndex(newestXact) != 0 &&
876 : !TransactionIdEquals(newestXact, FirstNormalTransactionId))
877 254962 : return;
878 :
879 322 : pageno = TransactionIdToPage(newestXact);
880 :
881 322 : LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
882 :
883 : /* Zero the page and make an XLOG entry about it */
884 322 : ZeroCLOGPage(pageno, true);
885 :
886 322 : LWLockRelease(CLogControlLock);
887 : }
888 :
889 :
890 : /*
891 : * Remove all CLOG segments before the one holding the passed transaction ID
892 : *
893 : * Before removing any CLOG data, we must flush XLOG to disk, to ensure
894 : * that any recently-emitted FREEZE_PAGE records have reached disk; otherwise
895 : * a crash and restart might leave us with some unfrozen tuples referencing
896 : * removed CLOG data. We choose to emit a special TRUNCATE XLOG record too.
897 : * Replaying the deletion from XLOG is not critical, since the files could
898 : * just as well be removed later, but doing so prevents a long-running hot
899 : * standby server from acquiring an unreasonably bloated CLOG directory.
900 : *
901 : * Since CLOG segments hold a large number of transactions, the opportunity to
902 : * actually remove a segment is fairly rare, and so it seems best not to do
903 : * the XLOG flush unless we have confirmed that there is a removable segment.
904 : */
905 : void
906 700 : TruncateCLOG(TransactionId oldestXact, Oid oldestxid_datoid)
907 : {
908 : int cutoffPage;
909 :
910 : /*
911 : * The cutoff point is the start of the segment containing oldestXact. We
912 : * pass the *page* containing oldestXact to SimpleLruTruncate.
913 : */
914 700 : cutoffPage = TransactionIdToPage(oldestXact);
915 :
916 : /* Check to see if there's any files that could be removed */
917 700 : if (!SlruScanDirectory(ClogCtl, SlruScanDirCbReportPresence, &cutoffPage))
918 700 : return; /* nothing to remove */
919 :
920 : /*
921 : * Advance oldestClogXid before truncating clog, so concurrent xact status
922 : * lookups can ensure they don't attempt to access truncated-away clog.
923 : *
924 : * It's only necessary to do this if we will actually truncate away clog
925 : * pages.
926 : */
927 0 : AdvanceOldestClogXid(oldestXact);
928 :
929 : /*
930 : * Write XLOG record and flush XLOG to disk. We record the oldest xid
931 : * we're keeping information about here so we can ensure that it's always
932 : * ahead of clog truncation in case we crash, and so a standby finds out
933 : * the new valid xid before the next checkpoint.
934 : */
935 0 : WriteTruncateXlogRec(cutoffPage, oldestXact, oldestxid_datoid);
936 :
937 : /* Now we can remove the old CLOG segment(s) */
938 0 : SimpleLruTruncate(ClogCtl, cutoffPage);
939 : }
940 :
941 :
942 : /*
943 : * Decide which of two CLOG page numbers is "older" for truncation purposes.
944 : *
945 : * We need to use comparison of TransactionIds here in order to do the right
946 : * thing with wraparound XID arithmetic. However, if we are asked about
947 : * page number zero, we don't want to hand InvalidTransactionId to
948 : * TransactionIdPrecedes: it'll get weird about permanent xact IDs. So,
949 : * offset both xids by FirstNormalTransactionId to avoid that.
950 : */
951 : static bool
952 700 : CLOGPagePrecedes(int page1, int page2)
953 : {
954 : TransactionId xid1;
955 : TransactionId xid2;
956 :
957 700 : xid1 = ((TransactionId) page1) * CLOG_XACTS_PER_PAGE;
958 700 : xid1 += FirstNormalTransactionId;
959 700 : xid2 = ((TransactionId) page2) * CLOG_XACTS_PER_PAGE;
960 700 : xid2 += FirstNormalTransactionId;
961 :
962 700 : return TransactionIdPrecedes(xid1, xid2);
963 : }
964 :
965 :
966 : /*
967 : * Write a ZEROPAGE xlog record
968 : */
969 : static void
970 322 : WriteZeroPageXlogRec(int pageno)
971 : {
972 322 : XLogBeginInsert();
973 322 : XLogRegisterData((char *) (&pageno), sizeof(int));
974 322 : (void) XLogInsert(RM_CLOG_ID, CLOG_ZEROPAGE);
975 322 : }
976 :
977 : /*
978 : * Write a TRUNCATE xlog record
979 : *
980 : * We must flush the xlog record to disk before returning --- see notes
981 : * in TruncateCLOG().
982 : */
983 : static void
984 0 : WriteTruncateXlogRec(int pageno, TransactionId oldestXact, Oid oldestXactDb)
985 : {
986 : XLogRecPtr recptr;
987 : xl_clog_truncate xlrec;
988 :
989 0 : xlrec.pageno = pageno;
990 0 : xlrec.oldestXact = oldestXact;
991 0 : xlrec.oldestXactDb = oldestXactDb;
992 :
993 0 : XLogBeginInsert();
994 0 : XLogRegisterData((char *) (&xlrec), sizeof(xl_clog_truncate));
995 0 : recptr = XLogInsert(RM_CLOG_ID, CLOG_TRUNCATE);
996 0 : XLogFlush(recptr);
997 0 : }
998 :
999 : /*
1000 : * CLOG resource manager's routines
1001 : */
1002 : void
1003 0 : clog_redo(XLogReaderState *record)
1004 : {
1005 0 : uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
1006 :
1007 : /* Backup blocks are not used in clog records */
1008 : Assert(!XLogRecHasAnyBlockRefs(record));
1009 :
1010 0 : if (info == CLOG_ZEROPAGE)
1011 : {
1012 : int pageno;
1013 : int slotno;
1014 :
1015 0 : memcpy(&pageno, XLogRecGetData(record), sizeof(int));
1016 :
1017 0 : LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
1018 :
1019 0 : slotno = ZeroCLOGPage(pageno, false);
1020 0 : SimpleLruWritePage(ClogCtl, slotno);
1021 : Assert(!ClogCtl->shared->page_dirty[slotno]);
1022 :
1023 0 : LWLockRelease(CLogControlLock);
1024 : }
1025 0 : else if (info == CLOG_TRUNCATE)
1026 : {
1027 : xl_clog_truncate xlrec;
1028 :
1029 0 : memcpy(&xlrec, XLogRecGetData(record), sizeof(xl_clog_truncate));
1030 :
1031 : /*
1032 : * During XLOG replay, latest_page_number isn't set up yet; insert a
1033 : * suitable value to bypass the sanity test in SimpleLruTruncate.
1034 : */
1035 0 : ClogCtl->shared->latest_page_number = xlrec.pageno;
1036 :
1037 0 : AdvanceOldestClogXid(xlrec.oldestXact);
1038 :
1039 0 : SimpleLruTruncate(ClogCtl, xlrec.pageno);
1040 : }
1041 : else
1042 0 : elog(PANIC, "clog_redo: unknown op code %u", info);
1043 0 : }
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