diff options
Diffstat (limited to 'src/backend/access/transam/xlog.c')
| -rw-r--r-- | src/backend/access/transam/xlog.c | 53 |
1 files changed, 40 insertions, 13 deletions
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f3e02dd6316..f70a3d5dd0e 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -7,7 +7,7 @@ * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.266 2007/04/03 04:14:26 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.267 2007/04/03 16:34:35 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -5366,6 +5366,8 @@ CreateCheckPoint(bool shutdown, bool force) int nsegsadded = 0; int nsegsremoved = 0; int nsegsrecycled = 0; + TransactionId *inCommitXids; + int nInCommit; /* * Acquire CheckpointLock to ensure only one checkpoint happens at a time. @@ -5392,14 +5394,9 @@ CreateCheckPoint(bool shutdown, bool force) checkPoint.time = time(NULL); /* - * We must hold CheckpointStartLock while determining the checkpoint REDO - * pointer. This ensures that any concurrent transaction commits will be - * either not yet logged, or logged and recorded in pg_clog. See notes in - * RecordTransactionCommit(). + * We must hold WALInsertLock while examining insert state to determine + * the checkpoint REDO pointer. */ - LWLockAcquire(CheckpointStartLock, LW_EXCLUSIVE); - - /* And we need WALInsertLock too */ LWLockAcquire(WALInsertLock, LW_EXCLUSIVE); /* @@ -5431,7 +5428,6 @@ CreateCheckPoint(bool shutdown, bool force) ControlFile->checkPointCopy.redo.xrecoff) { LWLockRelease(WALInsertLock); - LWLockRelease(CheckpointStartLock); LWLockRelease(CheckpointLock); END_CRIT_SECTION(); return; @@ -5476,18 +5472,49 @@ CreateCheckPoint(bool shutdown, bool force) } /* - * Now we can release insert lock and checkpoint start lock, allowing - * other xacts to proceed even while we are flushing disk buffers. + * Now we can release WAL insert lock, allowing other xacts to proceed + * while we are flushing disk buffers. */ LWLockRelease(WALInsertLock); - LWLockRelease(CheckpointStartLock); - if (!shutdown) ereport(DEBUG2, (errmsg("checkpoint starting"))); /* + * Before flushing data, we must wait for any transactions that are + * currently in their commit critical sections. If an xact inserted its + * commit record into XLOG just before the REDO point, then a crash + * restart from the REDO point would not replay that record, which means + * that our flushing had better include the xact's update of pg_clog. So + * we wait till he's out of his commit critical section before proceeding. + * See notes in RecordTransactionCommit(). + * + * Because we've already released WALInsertLock, this test is a bit fuzzy: + * it is possible that we will wait for xacts we didn't really need to + * wait for. But the delay should be short and it seems better to make + * checkpoint take a bit longer than to hold locks longer than necessary. + * (In fact, the whole reason we have this issue is that xact.c does + * commit record XLOG insertion and clog update as two separate steps + * protected by different locks, but again that seems best on grounds + * of minimizing lock contention.) + * + * A transaction that has not yet set inCommit when we look cannot be + * at risk, since he's not inserted his commit record yet; and one that's + * already cleared it is not at risk either, since he's done fixing clog + * and we will correctly flush the update below. So we cannot miss any + * xacts we need to wait for. + */ + nInCommit = GetTransactionsInCommit(&inCommitXids); + if (nInCommit > 0) + { + do { + pg_usleep(10000L); /* wait for 10 msec */ + } while (HaveTransactionsInCommit(inCommitXids, nInCommit)); + } + pfree(inCommitXids); + + /* * Get the other info we need for the checkpoint record. */ LWLockAcquire(XidGenLock, LW_SHARED); |