diff options
Diffstat (limited to 'src/backend/access/transam/clog.c')
| -rw-r--r-- | src/backend/access/transam/clog.c | 74 |
1 files changed, 61 insertions, 13 deletions
diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c index f57bdefa3a0..5817239a374 100644 --- a/src/backend/access/transam/clog.c +++ b/src/backend/access/transam/clog.c @@ -24,7 +24,7 @@ * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/backend/access/transam/clog.c,v 1.40 2006/10/04 00:29:49 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/access/transam/clog.c,v 1.41 2006/11/05 22:42:07 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -69,6 +69,7 @@ static SlruCtlData ClogCtlData; static int ZeroCLOGPage(int pageno, bool writeXlog); static bool CLOGPagePrecedes(int page1, int page2); static void WriteZeroPageXlogRec(int pageno); +static void WriteTruncateXlogRec(int pageno); /* @@ -309,16 +310,17 @@ ExtendCLOG(TransactionId newestXact) /* * Remove all CLOG segments before the one holding the passed transaction ID * - * When this is called, we know that the database logically contains no - * reference to transaction IDs older than oldestXact. However, we must - * not truncate the CLOG until we have performed a checkpoint, to ensure - * that no such references remain on disk either; else a crash just after - * the truncation might leave us with a problem. Since CLOG segments hold - * a large number of transactions, the opportunity to actually remove a - * segment is fairly rare, and so it seems best not to do the checkpoint - * unless we have confirmed that there is a removable segment. Therefore - * we issue the checkpoint command here, not in higher-level code as might - * seem cleaner. + * Before removing any CLOG data, we must flush XLOG to disk, to ensure + * that any recently-emitted HEAP_FREEZE records have reached disk; otherwise + * a crash and restart might leave us with some unfrozen tuples referencing + * removed CLOG data. We choose to emit a special TRUNCATE XLOG record too. + * Replaying the deletion from XLOG is not critical, since the files could + * just as well be removed later, but doing so prevents a long-running hot + * standby server from acquiring an unreasonably bloated CLOG directory. + * + * Since CLOG segments hold a large number of transactions, the opportunity to + * actually remove a segment is fairly rare, and so it seems best not to do + * the XLOG flush unless we have confirmed that there is a removable segment. */ void TruncateCLOG(TransactionId oldestXact) @@ -335,8 +337,8 @@ TruncateCLOG(TransactionId oldestXact) if (!SlruScanDirectory(ClogCtl, cutoffPage, false)) return; /* nothing to remove */ - /* Perform a CHECKPOINT */ - RequestCheckpoint(true, false); + /* Write XLOG record and flush XLOG to disk */ + WriteTruncateXlogRec(cutoffPage); /* Now we can remove the old CLOG segment(s) */ SimpleLruTruncate(ClogCtl, cutoffPage); @@ -387,6 +389,29 @@ WriteZeroPageXlogRec(int pageno) } /* + * Write a TRUNCATE xlog record + * + * We must flush the xlog record to disk before returning --- see notes + * in TruncateCLOG(). + * + * Note: xlog record is marked as outside transaction control, since we + * want it to be redone whether the invoking transaction commits or not. + */ +static void +WriteTruncateXlogRec(int pageno) +{ + XLogRecData rdata; + XLogRecPtr recptr; + + rdata.data = (char *) (&pageno); + rdata.len = sizeof(int); + rdata.buffer = InvalidBuffer; + rdata.next = NULL; + recptr = XLogInsert(RM_CLOG_ID, CLOG_TRUNCATE | XLOG_NO_TRAN, &rdata); + XLogFlush(recptr); +} + +/* * CLOG resource manager's routines */ void @@ -409,6 +434,22 @@ clog_redo(XLogRecPtr lsn, XLogRecord *record) LWLockRelease(CLogControlLock); } + else if (info == CLOG_TRUNCATE) + { + int pageno; + + memcpy(&pageno, XLogRecGetData(record), sizeof(int)); + + /* + * During XLOG replay, latest_page_number isn't set up yet; insert + * a suitable value to bypass the sanity test in SimpleLruTruncate. + */ + ClogCtl->shared->latest_page_number = pageno; + + SimpleLruTruncate(ClogCtl, pageno); + } + else + elog(PANIC, "clog_redo: unknown op code %u", info); } void @@ -423,6 +464,13 @@ clog_desc(StringInfo buf, uint8 xl_info, char *rec) memcpy(&pageno, rec, sizeof(int)); appendStringInfo(buf, "zeropage: %d", pageno); } + else if (info == CLOG_TRUNCATE) + { + int pageno; + + memcpy(&pageno, rec, sizeof(int)); + appendStringInfo(buf, "truncate before: %d", pageno); + } else appendStringInfo(buf, "UNKNOWN"); } |