diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 356a2f0c4c..e930731b16 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -1017,6 +1017,10 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
OldSnapshotTimeMapLock
Waiting to read or update old snapshot control information.
+
+ CLogTruncationLock
+ Waiting to truncate the transaction log or waiting for transaction log truncation to finish.
+
clog
Waiting for I/O on a clog (transaction status) buffer.
diff --git a/src/backend/access/rmgrdesc/clogdesc.c b/src/backend/access/rmgrdesc/clogdesc.c
index 352de48dbe..ef268c5ab3 100644
--- a/src/backend/access/rmgrdesc/clogdesc.c
+++ b/src/backend/access/rmgrdesc/clogdesc.c
@@ -23,12 +23,20 @@ clog_desc(StringInfo buf, XLogReaderState *record)
char *rec = XLogRecGetData(record);
uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
- if (info == CLOG_ZEROPAGE || info == CLOG_TRUNCATE)
+ if (info == CLOG_ZEROPAGE)
{
int pageno;
memcpy(&pageno, rec, sizeof(int));
- appendStringInfo(buf, "%d", pageno);
+ appendStringInfo(buf, "page %d", pageno);
+ }
+ else if (info == CLOG_TRUNCATE)
+ {
+ xl_clog_truncate xlrec;
+
+ memcpy(&xlrec, rec, sizeof(xl_clog_truncate));
+ appendStringInfo(buf, "page %d; oldestXact %u",
+ xlrec.pageno, xlrec.oldestXact);
}
}
diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c
index 5b1d13dac1..2d33510930 100644
--- a/src/backend/access/transam/clog.c
+++ b/src/backend/access/transam/clog.c
@@ -83,7 +83,8 @@ 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);
+static void WriteTruncateXlogRec(int pageno, TransactionId oldestXact,
+ Oid oldestXidDb);
static void TransactionIdSetPageStatus(TransactionId xid, int nsubxids,
TransactionId *subxids, XidStatus status,
XLogRecPtr lsn, int pageno);
@@ -640,7 +641,7 @@ ExtendCLOG(TransactionId newestXact)
* the XLOG flush unless we have confirmed that there is a removable segment.
*/
void
-TruncateCLOG(TransactionId oldestXact)
+TruncateCLOG(TransactionId oldestXact, Oid oldestxid_datoid)
{
int cutoffPage;
@@ -654,8 +655,26 @@ TruncateCLOG(TransactionId oldestXact)
if (!SlruScanDirectory(ClogCtl, SlruScanDirCbReportPresence, &cutoffPage))
return; /* nothing to remove */
- /* Write XLOG record and flush XLOG to disk */
- WriteTruncateXlogRec(cutoffPage);
+ /*
+ * Advance oldestClogXid before truncating clog, so concurrent xact status
+ * lookups can ensure they don't attempt to access truncated-away clog.
+ *
+ * It's only necessary to do this if we will actually truncate away clog
+ * pages.
+ */
+ AdvanceOldestClogXid(oldestXact);
+
+ /* vac_truncate_clog already advanced oldestXid */
+ Assert(TransactionIdPrecedesOrEquals(oldestXact,
+ ShmemVariableCache->oldestXid));
+
+ /*
+ * Write XLOG record and flush XLOG to disk. We record the oldest xid we're
+ * keeping information about here so we can ensure that it's always ahead
+ * of clog truncation in case we crash, and so a standby finds out the new
+ * valid xid before the next checkpoint.
+ */
+ WriteTruncateXlogRec(cutoffPage, oldestXact, oldestxid_datoid);
/* Now we can remove the old CLOG segment(s) */
SimpleLruTruncate(ClogCtl, cutoffPage);
@@ -704,12 +723,17 @@ WriteZeroPageXlogRec(int pageno)
* in TruncateCLOG().
*/
static void
-WriteTruncateXlogRec(int pageno)
+WriteTruncateXlogRec(int pageno, TransactionId oldestXact, Oid oldestXactDb)
{
XLogRecPtr recptr;
+ xl_clog_truncate xlrec;
+
+ xlrec.pageno = pageno;
+ xlrec.oldestXact = oldestXact;
+ xlrec.oldestXactDb = oldestXactDb;
XLogBeginInsert();
- XLogRegisterData((char *) (&pageno), sizeof(int));
+ XLogRegisterData((char *) (&xlrec), sizeof(xl_clog_truncate));
recptr = XLogInsert(RM_CLOG_ID, CLOG_TRUNCATE);
XLogFlush(recptr);
}
@@ -742,17 +766,19 @@ clog_redo(XLogReaderState *record)
}
else if (info == CLOG_TRUNCATE)
{
- int pageno;
+ xl_clog_truncate xlrec;
- memcpy(&pageno, XLogRecGetData(record), sizeof(int));
+ memcpy(&xlrec, XLogRecGetData(record), sizeof(xl_clog_truncate));
/*
* 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;
+ ClogCtl->shared->latest_page_number = xlrec.pageno;
- SimpleLruTruncate(ClogCtl, pageno);
+ AdvanceOldestClogXid(xlrec.oldestXact);
+
+ SimpleLruTruncate(ClogCtl, xlrec.pageno);
}
else
elog(PANIC, "clog_redo: unknown op code %u", info);
diff --git a/src/backend/access/transam/transam.c b/src/backend/access/transam/transam.c
index b91a259e80..562b53be9a 100644
--- a/src/backend/access/transam/transam.c
+++ b/src/backend/access/transam/transam.c
@@ -119,7 +119,7 @@ TransactionLogFetch(TransactionId transactionId)
* True iff transaction associated with the identifier did commit.
*
* Note:
- * Assumes transaction identifier is valid.
+ * Assumes transaction identifier is valid and exists in clog.
*/
bool /* true if given transaction committed */
TransactionIdDidCommit(TransactionId transactionId)
@@ -175,7 +175,7 @@ TransactionIdDidCommit(TransactionId transactionId)
* True iff transaction associated with the identifier did abort.
*
* Note:
- * Assumes transaction identifier is valid.
+ * Assumes transaction identifier is valid and exists in clog.
*/
bool /* true if given transaction aborted */
TransactionIdDidAbort(TransactionId transactionId)
diff --git a/src/backend/access/transam/varsup.c b/src/backend/access/transam/varsup.c
index 42fc351f7b..5efbfbd3d6 100644
--- a/src/backend/access/transam/varsup.c
+++ b/src/backend/access/transam/varsup.c
@@ -259,7 +259,28 @@ ReadNewTransactionId(void)
}
/*
- * Determine the last safe XID to allocate given the currently oldest
+ * Advance the cluster-wide value for the oldest valid clog entry.
+ *
+ * We must acquire CLogTruncationLock to advance the oldestClogXid. It's not
+ * necessary to hold the lock during the actual clog truncation, only when we
+ * advance the limit, as code looking up arbitrary xids is required to hold
+ * CLogTruncationLock from when it tests oldestClogXid through to when it
+ * completes the clog lookup.
+ */
+void
+AdvanceOldestClogXid(TransactionId oldest_datfrozenxid)
+{
+ LWLockAcquire(CLogTruncationLock, LW_EXCLUSIVE);
+ if (TransactionIdPrecedes(ShmemVariableCache->oldestClogXid,
+ oldest_datfrozenxid))
+ {
+ ShmemVariableCache->oldestClogXid = oldest_datfrozenxid;
+ }
+ LWLockRelease(CLogTruncationLock);
+}
+
+/*
+ * Determine the last safe XID to allocate using the currently oldest
* datfrozenxid (ie, the oldest XID that might exist in any database
* of our cluster), and the OID of the (or a) database with that value.
*/
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index de1937e013..b99ded5df6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5016,6 +5016,7 @@ BootStrapXLOG(void)
ShmemVariableCache->nextOid = checkPoint.nextOid;
ShmemVariableCache->oidCount = 0;
MultiXactSetNextMXact(checkPoint.nextMulti, checkPoint.nextMultiOffset);
+ AdvanceOldestClogXid(checkPoint.oldestXid);
SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
SetMultiXactIdLimit(checkPoint.oldestMulti, checkPoint.oldestMultiDB, true);
SetCommitTsLimit(InvalidTransactionId, InvalidTransactionId);
@@ -6622,6 +6623,7 @@ StartupXLOG(void)
ShmemVariableCache->nextOid = checkPoint.nextOid;
ShmemVariableCache->oidCount = 0;
MultiXactSetNextMXact(checkPoint.nextMulti, checkPoint.nextMultiOffset);
+ AdvanceOldestClogXid(checkPoint.oldestXid);
SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
SetMultiXactIdLimit(checkPoint.oldestMulti, checkPoint.oldestMultiDB, true);
SetCommitTsLimit(checkPoint.oldestCommitTsXid,
@@ -8687,6 +8689,11 @@ CreateCheckPoint(int flags)
/*
* Get the other info we need for the checkpoint record.
+ *
+ * We don't need to save oldestClogXid in the checkpoint, it only matters
+ * for the short period in which clog is being truncated, and if we crash
+ * during that we'll redo the clog truncation and fix up oldestClogXid
+ * there.
*/
LWLockAcquire(XidGenLock, LW_SHARED);
checkPoint.nextXid = ShmemVariableCache->nextXid;
@@ -9616,6 +9623,10 @@ xlog_redo(XLogReaderState *record)
MultiXactAdvanceOldest(checkPoint.oldestMulti,
checkPoint.oldestMultiDB);
+ /*
+ * No need to set oldestClogXid here as well; it'll be set when we
+ * redo an xl_clog_truncate if it changed since initialization.
+ */
SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
/*
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index d8ae3e1e43..9fbb0eb4eb 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -1194,7 +1194,7 @@ vac_truncate_clog(TransactionId frozenXID,
/*
* Truncate CLOG, multixact and CommitTs to the oldest computed value.
*/
- TruncateCLOG(frozenXID);
+ TruncateCLOG(frozenXID, oldestxid_datoid);
TruncateCommitTs(frozenXID);
TruncateMultiXact(minMulti, minmulti_datoid);
diff --git a/src/backend/storage/lmgr/lwlocknames.txt b/src/backend/storage/lmgr/lwlocknames.txt
index cd8b08f50d..e6025ecedb 100644
--- a/src/backend/storage/lmgr/lwlocknames.txt
+++ b/src/backend/storage/lmgr/lwlocknames.txt
@@ -49,3 +49,4 @@ MultiXactTruncationLock 41
OldSnapshotTimeMapLock 42
BackendRandomLock 43
LogicalRepWorkerLock 44
+CLogTruncationLock 45
diff --git a/src/include/access/clog.h b/src/include/access/clog.h
index 2894bd5620..60a9e11a0f 100644
--- a/src/include/access/clog.h
+++ b/src/include/access/clog.h
@@ -28,6 +28,12 @@ typedef int XidStatus;
#define TRANSACTION_STATUS_ABORTED 0x02
#define TRANSACTION_STATUS_SUB_COMMITTED 0x03
+typedef struct xl_clog_truncate
+{
+ int pageno;
+ TransactionId oldestXact;
+ Oid oldestXactDb;
+} xl_clog_truncate;
extern void TransactionIdSetTreeStatus(TransactionId xid, int nsubxids,
TransactionId *subxids, XidStatus status, XLogRecPtr lsn);
@@ -42,7 +48,7 @@ extern void TrimCLOG(void);
extern void ShutdownCLOG(void);
extern void CheckPointCLOG(void);
extern void ExtendCLOG(TransactionId newestXact);
-extern void TruncateCLOG(TransactionId oldestXact);
+extern void TruncateCLOG(TransactionId oldestXact, Oid oldestxid_datoid);
/* XLOG stuff */
#define CLOG_ZEROPAGE 0x00
diff --git a/src/include/access/transam.h b/src/include/access/transam.h
index 522c104073..d25a2dd207 100644
--- a/src/include/access/transam.h
+++ b/src/include/access/transam.h
@@ -134,6 +134,12 @@ typedef struct VariableCacheData
*/
TransactionId latestCompletedXid; /* newest XID that has committed or
* aborted */
+
+ /*
+ * These fields are protected by CLogTruncationLock
+ */
+ TransactionId oldestClogXid; /* oldest it's safe to look up in clog */
+
} VariableCacheData;
typedef VariableCacheData *VariableCache;
@@ -173,6 +179,7 @@ extern TransactionId GetNewTransactionId(bool isSubXact);
extern TransactionId ReadNewTransactionId(void);
extern void SetTransactionIdLimit(TransactionId oldest_datfrozenxid,
Oid oldest_datoid);
+extern void AdvanceOldestClogXid(TransactionId oldest_datfrozenxid);
extern bool ForceTransactionIdLimitUpdate(void);
extern Oid GetNewObjectId(void);
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 7957cab98c..c09c0f8e5f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD096 /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD097 /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{