1 /*-------------------------------------------------------------------------
4 * PostgreSQL transaction-commit-log manager
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.
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.
26 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
27 * Portions Copyright (c) 1994, Regents of the University of California
29 * src/backend/access/transam/clog.c
31 *-------------------------------------------------------------------------
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"
45 * Defines for CLOG page sizes. A page is the same BLCKSZ as is used
46 * everywhere else in Postgres.
48 * Note: because TransactionIds are 32 bits and wrap around at 0xFFFFFFFF,
49 * CLOG page numbering also wraps around at 0xFFFFFFFF/CLOG_XACTS_PER_PAGE,
50 * and CLOG segment numbering at
51 * 0xFFFFFFFF/CLOG_XACTS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need take no
52 * explicit notice of that fact in this module, except when comparing segment
53 * and page numbers in TruncateCLOG (see CLOGPagePrecedes).
56 /* We need two bits per xact, so four xacts fit in a byte */
57 #define CLOG_BITS_PER_XACT 2
58 #define CLOG_XACTS_PER_BYTE 4
59 #define CLOG_XACTS_PER_PAGE (BLCKSZ * CLOG_XACTS_PER_BYTE)
60 #define CLOG_XACT_BITMASK ((1 << CLOG_BITS_PER_XACT) - 1)
62 #define TransactionIdToPage(xid) ((xid) / (TransactionId) CLOG_XACTS_PER_PAGE)
63 #define TransactionIdToPgIndex(xid) ((xid) % (TransactionId) CLOG_XACTS_PER_PAGE)
64 #define TransactionIdToByte(xid) (TransactionIdToPgIndex(xid) / CLOG_XACTS_PER_BYTE)
65 #define TransactionIdToBIndex(xid) ((xid) % (TransactionId) CLOG_XACTS_PER_BYTE)
67 /* We store the latest async LSN for each group of transactions */
68 #define CLOG_XACTS_PER_LSN_GROUP 32 /* keep this a power of 2 */
69 #define CLOG_LSNS_PER_PAGE (CLOG_XACTS_PER_PAGE / CLOG_XACTS_PER_LSN_GROUP)
71 #define GetLSNIndex(slotno, xid) ((slotno) * CLOG_LSNS_PER_PAGE + \
72 ((xid) % (TransactionId) CLOG_XACTS_PER_PAGE) / CLOG_XACTS_PER_LSN_GROUP)
76 * Link to shared-memory data structures for CLOG control
78 static SlruCtlData ClogCtlData;
80 #define ClogCtl (&ClogCtlData)
83 static int ZeroCLOGPage(int pageno, bool writeXlog);
84 static bool CLOGPagePrecedes(int page1, int page2);
85 static void WriteZeroPageXlogRec(int pageno);
86 static void WriteTruncateXlogRec(int pageno, TransactionId oldestXact,
88 static void TransactionIdSetPageStatus(TransactionId xid, int nsubxids,
89 TransactionId *subxids, XidStatus status,
90 XLogRecPtr lsn, int pageno);
91 static void TransactionIdSetStatusBit(TransactionId xid, XidStatus status,
92 XLogRecPtr lsn, int slotno);
93 static void set_status_by_pages(int nsubxids, TransactionId *subxids,
94 XidStatus status, XLogRecPtr lsn);
98 * TransactionIdSetTreeStatus
100 * Record the final state of transaction entries in the commit log for
101 * a transaction and its subtransaction tree. Take care to ensure this is
102 * efficient, and as atomic as possible.
104 * xid is a single xid to set status for. This will typically be
105 * the top level transactionid for a top level commit or abort. It can
106 * also be a subtransaction when we record transaction aborts.
108 * subxids is an array of xids of length nsubxids, representing subtransactions
109 * in the tree of xid. In various cases nsubxids may be zero.
111 * lsn must be the WAL location of the commit record when recording an async
112 * commit. For a synchronous commit it can be InvalidXLogRecPtr, since the
113 * caller guarantees the commit record is already flushed in that case. It
114 * should be InvalidXLogRecPtr for abort cases, too.
116 * In the commit case, atomicity is limited by whether all the subxids are in
117 * the same CLOG page as xid. If they all are, then the lock will be grabbed
118 * only once, and the status will be set to committed directly. Otherwise
120 * 1. set sub-committed all subxids that are not on the same page as the
122 * 2. atomically set committed the main xid and the subxids on the same page
123 * 3. go over the first bunch again and set them committed
124 * Note that as far as concurrent checkers are concerned, main transaction
125 * commit as a whole is still atomic.
128 * TransactionId t commits and has subxids t1, t2, t3, t4
129 * t is on page p1, t1 is also on p1, t2 and t3 are on p2, t4 is on p3
130 * 1. update pages2-3:
131 * page2: set t2,t3 as sub-committed
132 * page3: set t4 as sub-committed
134 * set t1 as sub-committed,
135 * then set t as committed,
136 then set t1 as committed
137 * 3. update pages2-3:
138 * page2: set t2,t3 as committed
139 * page3: set t4 as committed
141 * NB: this is a low-level routine and is NOT the preferred entry point
142 * for most uses; functions in transam.c are the intended callers.
144 * XXX Think about issuing FADVISE_WILLNEED on pages that we will need,
145 * but aren't yet in cache, as well as hinting pages not to fall out of
149 TransactionIdSetTreeStatus(TransactionId xid, int nsubxids,
150 TransactionId *subxids, XidStatus status, XLogRecPtr lsn)
152 int pageno = TransactionIdToPage(xid); /* get page of parent */
155 Assert(status == TRANSACTION_STATUS_COMMITTED ||
156 status == TRANSACTION_STATUS_ABORTED);
159 * See how many subxids, if any, are on the same page as the parent, if
162 for (i = 0; i < nsubxids; i++)
164 if (TransactionIdToPage(subxids[i]) != pageno)
169 * Do all items fit on a single page?
174 * Set the parent and all subtransactions in a single call
176 TransactionIdSetPageStatus(xid, nsubxids, subxids, status, lsn,
181 int nsubxids_on_first_page = i;
184 * If this is a commit then we care about doing this correctly (i.e.
185 * using the subcommitted intermediate status). By here, we know
186 * we're updating more than one page of clog, so we must mark entries
187 * that are *not* on the first page so that they show as subcommitted
188 * before we then return to update the status to fully committed.
190 * To avoid touching the first page twice, skip marking subcommitted
191 * for the subxids on that first page.
193 if (status == TRANSACTION_STATUS_COMMITTED)
194 set_status_by_pages(nsubxids - nsubxids_on_first_page,
195 subxids + nsubxids_on_first_page,
196 TRANSACTION_STATUS_SUB_COMMITTED, lsn);
199 * Now set the parent and subtransactions on same page as the parent,
202 pageno = TransactionIdToPage(xid);
203 TransactionIdSetPageStatus(xid, nsubxids_on_first_page, subxids, status,
207 * Now work through the rest of the subxids one clog page at a time,
208 * starting from the second page onwards, like we did above.
210 set_status_by_pages(nsubxids - nsubxids_on_first_page,
211 subxids + nsubxids_on_first_page,
217 * Helper for TransactionIdSetTreeStatus: set the status for a bunch of
218 * transactions, chunking in the separate CLOG pages involved. We never
219 * pass the whole transaction tree to this function, only subtransactions
220 * that are on different pages to the top level transaction id.
223 set_status_by_pages(int nsubxids, TransactionId *subxids,
224 XidStatus status, XLogRecPtr lsn)
226 int pageno = TransactionIdToPage(subxids[0]);
234 while (TransactionIdToPage(subxids[i]) == pageno && i < nsubxids)
240 TransactionIdSetPageStatus(InvalidTransactionId,
241 num_on_page, subxids + offset,
242 status, lsn, pageno);
244 pageno = TransactionIdToPage(subxids[offset]);
249 * Record the final state of transaction entries in the commit log for
250 * all entries on a single page. Atomic only on this page.
252 * Otherwise API is same as TransactionIdSetTreeStatus()
255 TransactionIdSetPageStatus(TransactionId xid, int nsubxids,
256 TransactionId *subxids, XidStatus status,
257 XLogRecPtr lsn, int pageno)
262 Assert(status == TRANSACTION_STATUS_COMMITTED ||
263 status == TRANSACTION_STATUS_ABORTED ||
264 (status == TRANSACTION_STATUS_SUB_COMMITTED && !TransactionIdIsValid(xid)));
266 LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
269 * If we're doing an async commit (ie, lsn is valid), then we must wait
270 * for any active write on the page slot to complete. Otherwise our
271 * update could reach disk in that write, which will not do since we
272 * mustn't let it reach disk until we've done the appropriate WAL flush.
273 * But when lsn is invalid, it's OK to scribble on a page while it is
274 * write-busy, since we don't care if the update reaches disk sooner than
277 slotno = SimpleLruReadPage(ClogCtl, pageno, XLogRecPtrIsInvalid(lsn), xid);
280 * Set the main transaction id, if any.
282 * If we update more than one xid on this page while it is being written
283 * out, we might find that some of the bits go to disk and others don't.
284 * If we are updating commits on the page with the top-level xid that
285 * could break atomicity, so we subcommit the subxids first before we mark
286 * the top-level commit.
288 if (TransactionIdIsValid(xid))
290 /* Subtransactions first, if needed ... */
291 if (status == TRANSACTION_STATUS_COMMITTED)
293 for (i = 0; i < nsubxids; i++)
295 Assert(ClogCtl->shared->page_number[slotno] == TransactionIdToPage(subxids[i]));
296 TransactionIdSetStatusBit(subxids[i],
297 TRANSACTION_STATUS_SUB_COMMITTED,
302 /* ... then the main transaction */
303 TransactionIdSetStatusBit(xid, status, lsn, slotno);
306 /* Set the subtransactions */
307 for (i = 0; i < nsubxids; i++)
309 Assert(ClogCtl->shared->page_number[slotno] == TransactionIdToPage(subxids[i]));
310 TransactionIdSetStatusBit(subxids[i], status, lsn, slotno);
313 ClogCtl->shared->page_dirty[slotno] = true;
315 LWLockRelease(CLogControlLock);
319 * Sets the commit status of a single transaction.
321 * Must be called with CLogControlLock held
324 TransactionIdSetStatusBit(TransactionId xid, XidStatus status, XLogRecPtr lsn, int slotno)
326 int byteno = TransactionIdToByte(xid);
327 int bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
332 byteptr = ClogCtl->shared->page_buffer[slotno] + byteno;
333 curval = (*byteptr >> bshift) & CLOG_XACT_BITMASK;
336 * When replaying transactions during recovery we still need to perform
337 * the two phases of subcommit and then commit. However, some transactions
338 * are already correctly marked, so we just treat those as a no-op which
339 * allows us to keep the following Assert as restrictive as possible.
341 if (InRecovery && status == TRANSACTION_STATUS_SUB_COMMITTED &&
342 curval == TRANSACTION_STATUS_COMMITTED)
346 * Current state change should be from 0 or subcommitted to target state
347 * or we should already be there when replaying changes during recovery.
349 Assert(curval == 0 ||
350 (curval == TRANSACTION_STATUS_SUB_COMMITTED &&
351 status != TRANSACTION_STATUS_IN_PROGRESS) ||
354 /* note this assumes exclusive access to the clog page */
356 byteval &= ~(((1 << CLOG_BITS_PER_XACT) - 1) << bshift);
357 byteval |= (status << bshift);
361 * Update the group LSN if the transaction completion LSN is higher.
363 * Note: lsn will be invalid when supplied during InRecovery processing,
364 * so we don't need to do anything special to avoid LSN updates during
365 * recovery. After recovery completes the next clog change will set the
368 if (!XLogRecPtrIsInvalid(lsn))
370 int lsnindex = GetLSNIndex(slotno, xid);
372 if (ClogCtl->shared->group_lsn[lsnindex] < lsn)
373 ClogCtl->shared->group_lsn[lsnindex] = lsn;
378 * Interrogate the state of a transaction in the commit log.
380 * Aside from the actual commit status, this function returns (into *lsn)
381 * an LSN that is late enough to be able to guarantee that if we flush up to
382 * that LSN then we will have flushed the transaction's commit record to disk.
383 * The result is not necessarily the exact LSN of the transaction's commit
384 * record! For example, for long-past transactions (those whose clog pages
385 * already migrated to disk), we'll return InvalidXLogRecPtr. Also, because
386 * we group transactions on the same clog page to conserve storage, we might
387 * return the LSN of a later transaction that falls into the same group.
389 * NB: this is a low-level routine and is NOT the preferred entry point
390 * for most uses; TransactionLogFetch() in transam.c is the intended caller.
393 TransactionIdGetStatus(TransactionId xid, XLogRecPtr *lsn)
395 int pageno = TransactionIdToPage(xid);
396 int byteno = TransactionIdToByte(xid);
397 int bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
403 /* lock is acquired by SimpleLruReadPage_ReadOnly */
405 slotno = SimpleLruReadPage_ReadOnly(ClogCtl, pageno, xid);
406 byteptr = ClogCtl->shared->page_buffer[slotno] + byteno;
408 status = (*byteptr >> bshift) & CLOG_XACT_BITMASK;
410 lsnindex = GetLSNIndex(slotno, xid);
411 *lsn = ClogCtl->shared->group_lsn[lsnindex];
413 LWLockRelease(CLogControlLock);
419 * Number of shared CLOG buffers.
421 * On larger multi-processor systems, it is possible to have many CLOG page
422 * requests in flight at one time which could lead to disk access for CLOG
423 * page if the required page is not found in memory. Testing revealed that we
424 * can get the best performance by having 128 CLOG buffers, more than that it
425 * doesn't improve performance.
427 * Unconditionally keeping the number of CLOG buffers to 128 did not seem like
428 * a good idea, because it would increase the minimum amount of shared memory
429 * required to start, which could be a problem for people running very small
430 * configurations. The following formula seems to represent a reasonable
431 * compromise: people with very low values for shared_buffers will get fewer
432 * CLOG buffers as well, and everyone else will get 128.
435 CLOGShmemBuffers(void)
437 return Min(128, Max(4, NBuffers / 512));
441 * Initialization of shared memory for CLOG
446 return SimpleLruShmemSize(CLOGShmemBuffers(), CLOG_LSNS_PER_PAGE);
452 ClogCtl->PagePrecedes = CLOGPagePrecedes;
453 SimpleLruInit(ClogCtl, "clog", CLOGShmemBuffers(), CLOG_LSNS_PER_PAGE,
454 CLogControlLock, "pg_xact", LWTRANCHE_CLOG_BUFFERS);
458 * This func must be called ONCE on system install. It creates
459 * the initial CLOG segment. (The CLOG directory is assumed to
460 * have been created by initdb, and CLOGShmemInit must have been
468 LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
470 /* Create and zero the first page of the commit log */
471 slotno = ZeroCLOGPage(0, false);
473 /* Make sure it's written out */
474 SimpleLruWritePage(ClogCtl, slotno);
475 Assert(!ClogCtl->shared->page_dirty[slotno]);
477 LWLockRelease(CLogControlLock);
481 * Initialize (or reinitialize) a page of CLOG to zeroes.
482 * If writeXlog is TRUE, also emit an XLOG record saying we did this.
484 * The page is not actually written, just set up in shared memory.
485 * The slot number of the new page is returned.
487 * Control lock must be held at entry, and will be held at exit.
490 ZeroCLOGPage(int pageno, bool writeXlog)
494 slotno = SimpleLruZeroPage(ClogCtl, pageno);
497 WriteZeroPageXlogRec(pageno);
503 * This must be called ONCE during postmaster or standalone-backend startup,
504 * after StartupXLOG has initialized ShmemVariableCache->nextXid.
509 TransactionId xid = ShmemVariableCache->nextXid;
510 int pageno = TransactionIdToPage(xid);
512 LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
515 * Initialize our idea of the latest page number.
517 ClogCtl->shared->latest_page_number = pageno;
519 LWLockRelease(CLogControlLock);
523 * This must be called ONCE at the end of startup/recovery.
528 TransactionId xid = ShmemVariableCache->nextXid;
529 int pageno = TransactionIdToPage(xid);
531 LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
534 * Re-Initialize our idea of the latest page number.
536 ClogCtl->shared->latest_page_number = pageno;
539 * Zero out the remainder of the current clog page. Under normal
540 * circumstances it should be zeroes already, but it seems at least
541 * theoretically possible that XLOG replay will have settled on a nextXID
542 * value that is less than the last XID actually used and marked by the
543 * previous database lifecycle (since subtransaction commit writes clog
544 * but makes no WAL entry). Let's just be safe. (We need not worry about
545 * pages beyond the current one, since those will be zeroed when first
546 * used. For the same reason, there is no need to do anything when
547 * nextXid is exactly at a page boundary; and it's likely that the
548 * "current" page doesn't exist yet in that case.)
550 if (TransactionIdToPgIndex(xid) != 0)
552 int byteno = TransactionIdToByte(xid);
553 int bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
557 slotno = SimpleLruReadPage(ClogCtl, pageno, false, xid);
558 byteptr = ClogCtl->shared->page_buffer[slotno] + byteno;
560 /* Zero so-far-unused positions in the current byte */
561 *byteptr &= (1 << bshift) - 1;
562 /* Zero the rest of the page */
563 MemSet(byteptr + 1, 0, BLCKSZ - byteno - 1);
565 ClogCtl->shared->page_dirty[slotno] = true;
568 LWLockRelease(CLogControlLock);
572 * This must be called ONCE during postmaster or standalone-backend shutdown
577 /* Flush dirty CLOG pages to disk */
578 TRACE_POSTGRESQL_CLOG_CHECKPOINT_START(false);
579 SimpleLruFlush(ClogCtl, false);
582 * fsync pg_xact to ensure that any files flushed previously are durably
585 fsync_fname("pg_xact", true);
587 TRACE_POSTGRESQL_CLOG_CHECKPOINT_DONE(false);
591 * Perform a checkpoint --- either during shutdown, or on-the-fly
596 /* Flush dirty CLOG pages to disk */
597 TRACE_POSTGRESQL_CLOG_CHECKPOINT_START(true);
598 SimpleLruFlush(ClogCtl, true);
601 * fsync pg_xact to ensure that any files flushed previously are durably
604 fsync_fname("pg_xact", true);
606 TRACE_POSTGRESQL_CLOG_CHECKPOINT_DONE(true);
611 * Make sure that CLOG has room for a newly-allocated XID.
613 * NB: this is called while holding XidGenLock. We want it to be very fast
614 * most of the time; even when it's not so fast, no actual I/O need happen
615 * unless we're forced to write out a dirty clog or xlog page to make room
619 ExtendCLOG(TransactionId newestXact)
624 * No work except at first XID of a page. But beware: just after
625 * wraparound, the first XID of page zero is FirstNormalTransactionId.
627 if (TransactionIdToPgIndex(newestXact) != 0 &&
628 !TransactionIdEquals(newestXact, FirstNormalTransactionId))
631 pageno = TransactionIdToPage(newestXact);
633 LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
635 /* Zero the page and make an XLOG entry about it */
636 ZeroCLOGPage(pageno, true);
638 LWLockRelease(CLogControlLock);
643 * Remove all CLOG segments before the one holding the passed transaction ID
645 * Before removing any CLOG data, we must flush XLOG to disk, to ensure
646 * that any recently-emitted HEAP_FREEZE records have reached disk; otherwise
647 * a crash and restart might leave us with some unfrozen tuples referencing
648 * removed CLOG data. We choose to emit a special TRUNCATE XLOG record too.
649 * Replaying the deletion from XLOG is not critical, since the files could
650 * just as well be removed later, but doing so prevents a long-running hot
651 * standby server from acquiring an unreasonably bloated CLOG directory.
653 * Since CLOG segments hold a large number of transactions, the opportunity to
654 * actually remove a segment is fairly rare, and so it seems best not to do
655 * the XLOG flush unless we have confirmed that there is a removable segment.
658 TruncateCLOG(TransactionId oldestXact, Oid oldestxid_datoid)
663 * The cutoff point is the start of the segment containing oldestXact. We
664 * pass the *page* containing oldestXact to SimpleLruTruncate.
666 cutoffPage = TransactionIdToPage(oldestXact);
668 /* Check to see if there's any files that could be removed */
669 if (!SlruScanDirectory(ClogCtl, SlruScanDirCbReportPresence, &cutoffPage))
670 return; /* nothing to remove */
673 * Advance oldestClogXid before truncating clog, so concurrent xact status
674 * lookups can ensure they don't attempt to access truncated-away clog.
676 * It's only necessary to do this if we will actually truncate away clog
679 AdvanceOldestClogXid(oldestXact);
681 /* vac_truncate_clog already advanced oldestXid */
682 Assert(TransactionIdPrecedesOrEquals(oldestXact,
683 ShmemVariableCache->oldestXid));
686 * Write XLOG record and flush XLOG to disk. We record the oldest xid
687 * we're keeping information about here so we can ensure that it's always
688 * ahead of clog truncation in case we crash, and so a standby finds out
689 * the new valid xid before the next checkpoint.
691 WriteTruncateXlogRec(cutoffPage, oldestXact, oldestxid_datoid);
693 /* Now we can remove the old CLOG segment(s) */
694 SimpleLruTruncate(ClogCtl, cutoffPage);
699 * Decide which of two CLOG page numbers is "older" for truncation purposes.
701 * We need to use comparison of TransactionIds here in order to do the right
702 * thing with wraparound XID arithmetic. However, if we are asked about
703 * page number zero, we don't want to hand InvalidTransactionId to
704 * TransactionIdPrecedes: it'll get weird about permanent xact IDs. So,
705 * offset both xids by FirstNormalTransactionId to avoid that.
708 CLOGPagePrecedes(int page1, int page2)
713 xid1 = ((TransactionId) page1) * CLOG_XACTS_PER_PAGE;
714 xid1 += FirstNormalTransactionId;
715 xid2 = ((TransactionId) page2) * CLOG_XACTS_PER_PAGE;
716 xid2 += FirstNormalTransactionId;
718 return TransactionIdPrecedes(xid1, xid2);
723 * Write a ZEROPAGE xlog record
726 WriteZeroPageXlogRec(int pageno)
729 XLogRegisterData((char *) (&pageno), sizeof(int));
730 (void) XLogInsert(RM_CLOG_ID, CLOG_ZEROPAGE);
734 * Write a TRUNCATE xlog record
736 * We must flush the xlog record to disk before returning --- see notes
740 WriteTruncateXlogRec(int pageno, TransactionId oldestXact, Oid oldestXactDb)
743 xl_clog_truncate xlrec;
745 xlrec.pageno = pageno;
746 xlrec.oldestXact = oldestXact;
747 xlrec.oldestXactDb = oldestXactDb;
750 XLogRegisterData((char *) (&xlrec), sizeof(xl_clog_truncate));
751 recptr = XLogInsert(RM_CLOG_ID, CLOG_TRUNCATE);
756 * CLOG resource manager's routines
759 clog_redo(XLogReaderState *record)
761 uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
763 /* Backup blocks are not used in clog records */
764 Assert(!XLogRecHasAnyBlockRefs(record));
766 if (info == CLOG_ZEROPAGE)
771 memcpy(&pageno, XLogRecGetData(record), sizeof(int));
773 LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
775 slotno = ZeroCLOGPage(pageno, false);
776 SimpleLruWritePage(ClogCtl, slotno);
777 Assert(!ClogCtl->shared->page_dirty[slotno]);
779 LWLockRelease(CLogControlLock);
781 else if (info == CLOG_TRUNCATE)
783 xl_clog_truncate xlrec;
785 memcpy(&xlrec, XLogRecGetData(record), sizeof(xl_clog_truncate));
788 * During XLOG replay, latest_page_number isn't set up yet; insert a
789 * suitable value to bypass the sanity test in SimpleLruTruncate.
791 ClogCtl->shared->latest_page_number = xlrec.pageno;
793 AdvanceOldestClogXid(xlrec.oldestXact);
795 SimpleLruTruncate(ClogCtl, xlrec.pageno);
798 elog(PANIC, "clog_redo: unknown op code %u", info);