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Track the oldest XID that can be safely looked up in CLOG.

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This provides infrastructure for looking up arbitrary, user-supplied
XIDs without a risk of scary-looking failures from within the clog
module.  Normally, the oldest XID that can be safely looked up in CLOG
is the same as the oldest XID that can reused without causing
wraparound, and the latter is already tracked.  However, while
truncation is in progress, the values are different, so we must
keep track of them separately.

Craig Ringer, reviewed by Simon Riggs and by me.

Discussion: http://postgr.es/m/CAMsr+YHQiWNEi0daCTboS40T+V5s_+dst3PYv_8v2wNVH+Xx4g@mail.gmail.com
This commit is contained in:
Robert Haas
2017-03-23 14:08:23 -04:00
parent 50c956add8
commit ea42cc18c3
11 changed files with 102 additions and 18 deletions
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8
src/include/access/clog.h
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@@ -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

7
src/include/access/transam.h
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@@ -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);

2
src/include/access/xlog_internal.h
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@@ -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
{