Make TransactionIdIsInProgress check transam.c's single-item XID status cache
before it goes groveling through the ProcArray. In situations where the same recently-committed transaction ID is checked repeatedly by tqual.c, this saves a lot of shared-memory searches. And it's cheap enough that it shouldn't hurt noticeably when it doesn't help. Concept and patch by Simon, some minor tweaking and comment-cleanup by Tom.
This commit is contained in:
Tom Lane
parent
ba8a9a9282
commit
611b4393f2
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@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.73 2008/01/01 19:45:48 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.74 2008/03/11 20:20:35 tgl Exp $
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*
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* NOTES
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* This file contains the high level access-method interface to the
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@ -25,12 +25,11 @@
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#include "utils/tqual.h"
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static XidStatus TransactionLogFetch(TransactionId transactionId);
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static void TransactionLogUpdate(TransactionId transactionId,
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XidStatus status, XLogRecPtr lsn);
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/*
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* Single-item cache for results of TransactionLogFetch.
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* Single-item cache for results of TransactionLogFetch. It's worth having
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* such a cache because we frequently find ourselves repeatedly checking the
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* same XID, for example when scanning a table just after a bulk insert,
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* update, or delete.
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*/
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static TransactionId cachedFetchXid = InvalidTransactionId;
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static XidStatus cachedFetchXidStatus;
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@ -39,9 +38,14 @@ static XLogRecPtr cachedCommitLSN;
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/* Handy constant for an invalid xlog recptr */
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static const XLogRecPtr InvalidXLogRecPtr = {0, 0};
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/* Local functions */
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static XidStatus TransactionLogFetch(TransactionId transactionId);
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static void TransactionLogUpdate(TransactionId transactionId,
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XidStatus status, XLogRecPtr lsn);
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/* ----------------------------------------------------------------
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* postgres log access method interface
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* Postgres log access method interface
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*
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* TransactionLogFetch
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* TransactionLogUpdate
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@ -82,8 +86,8 @@ TransactionLogFetch(TransactionId transactionId)
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xidstatus = TransactionIdGetStatus(transactionId, &xidlsn);
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/*
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* DO NOT cache status for unfinished or sub-committed transactions! We
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* only cache status that is guaranteed not to change.
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* Cache it, but DO NOT cache status for unfinished or sub-committed
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* transactions! We only cache status that is guaranteed not to change.
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*/
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if (xidstatus != TRANSACTION_STATUS_IN_PROGRESS &&
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xidstatus != TRANSACTION_STATUS_SUB_COMMITTED)
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@ -96,12 +100,11 @@ TransactionLogFetch(TransactionId transactionId)
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return xidstatus;
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}
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/* --------------------------------
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/*
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* TransactionLogUpdate
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*
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* Store the new status of a transaction. The commit record LSN must be
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* passed when recording an async commit; else it should be InvalidXLogRecPtr.
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* --------------------------------
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*/
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static inline void
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TransactionLogUpdate(TransactionId transactionId,
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@ -131,32 +134,27 @@ TransactionLogMultiUpdate(int nxids, TransactionId *xids,
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TransactionIdSetStatus(xids[i], status, lsn);
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}
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/* ----------------------------------------------------------------
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* Interface functions
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*
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* TransactionId DidCommit
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* TransactionId DidAbort
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* TransactionId IsInProgress
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* TransactionIdDidCommit
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* TransactionIdDidAbort
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* ========
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* these functions test the transaction status of
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* a specified transaction id.
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*
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* TransactionId Commit
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* TransactionId Abort
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* TransactionIdCommit
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* TransactionIdAbort
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* ========
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* these functions set the transaction status
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* of the specified xid.
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*
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* See also TransactionIdIsInProgress, which once was in this module
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* but now lives in procarray.c.
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* ----------------------------------------------------------------
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*/
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/* --------------------------------
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* TransactionId DidCommit
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* TransactionId DidAbort
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* TransactionId IsInProgress
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* --------------------------------
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*/
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/*
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* TransactionIdDidCommit
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* True iff transaction associated with the identifier did commit.
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@ -262,11 +260,33 @@ TransactionIdDidAbort(TransactionId transactionId)
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return false;
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}
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/* --------------------------------
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* TransactionId Commit
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* TransactionId Abort
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* --------------------------------
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/*
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* TransactionIdIsKnownCompleted
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* True iff transaction associated with the identifier is currently
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* known to have either committed or aborted.
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*
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* This does NOT look into pg_clog but merely probes our local cache
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* (and so it's not named TransactionIdDidComplete, which would be the
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* appropriate name for a function that worked that way). The intended
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* use is just to short-circuit TransactionIdIsInProgress calls when doing
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* repeated tqual.c checks for the same XID. If this isn't extremely fast
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* then it will be counterproductive.
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*
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* Note:
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* Assumes transaction identifier is valid.
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*/
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bool
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TransactionIdIsKnownCompleted(TransactionId transactionId)
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{
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if (TransactionIdEquals(transactionId, cachedFetchXid))
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{
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/* If it's in the cache at all, it must be completed. */
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return true;
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}
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return false;
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}
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/*
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* TransactionIdCommit
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@ -292,7 +312,6 @@ TransactionIdAsyncCommit(TransactionId transactionId, XLogRecPtr lsn)
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TransactionLogUpdate(transactionId, TRANSACTION_STATUS_COMMITTED, lsn);
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}
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/*
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* TransactionIdAbort
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* Aborts the transaction associated with the identifier.
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@ -352,7 +371,6 @@ TransactionIdAsyncCommitTree(int nxids, TransactionId *xids, XLogRecPtr lsn)
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lsn);
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}
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/*
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* TransactionIdAbortTree
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* Marks all the given transaction ids as aborted.
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@ -368,6 +386,7 @@ TransactionIdAbortTree(int nxids, TransactionId *xids)
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InvalidXLogRecPtr);
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}
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/*
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* TransactionIdPrecedes --- is id1 logically < id2?
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*/
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@ -23,7 +23,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.40 2008/01/09 21:52:36 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.41 2008/03/11 20:20:35 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -60,6 +60,7 @@ static ProcArrayStruct *procArray;
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/* counters for XidCache measurement */
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static long xc_by_recent_xmin = 0;
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static long xc_by_known_xact = 0;
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static long xc_by_my_xact = 0;
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static long xc_by_latest_xid = 0;
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static long xc_by_main_xid = 0;
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@ -68,6 +69,7 @@ static long xc_no_overflow = 0;
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static long xc_slow_answer = 0;
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#define xc_by_recent_xmin_inc() (xc_by_recent_xmin++)
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#define xc_by_known_xact_inc() (xc_by_known_xact++)
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#define xc_by_my_xact_inc() (xc_by_my_xact++)
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#define xc_by_latest_xid_inc() (xc_by_latest_xid++)
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#define xc_by_main_xid_inc() (xc_by_main_xid++)
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@ -79,6 +81,7 @@ static void DisplayXidCache(void);
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#else /* !XIDCACHE_DEBUG */
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#define xc_by_recent_xmin_inc() ((void) 0)
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#define xc_by_known_xact_inc() ((void) 0)
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#define xc_by_my_xact_inc() ((void) 0)
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#define xc_by_latest_xid_inc() ((void) 0)
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#define xc_by_main_xid_inc() ((void) 0)
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@ -353,6 +356,17 @@ TransactionIdIsInProgress(TransactionId xid)
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return false;
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}
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/*
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* We may have just checked the status of this transaction, so if it is
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* already known to be completed, we can fall out without any access to
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* shared memory.
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*/
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if (TransactionIdIsKnownCompleted(xid))
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{
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xc_by_known_xact_inc();
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return false;
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}
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/*
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* Also, we can handle our own transaction (and subtransactions) without
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* any access to shared memory.
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@ -1335,8 +1349,9 @@ static void
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DisplayXidCache(void)
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{
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fprintf(stderr,
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"XidCache: xmin: %ld, myxact: %ld, latest: %ld, mainxid: %ld, childxid: %ld, nooflo: %ld, slow: %ld\n",
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"XidCache: xmin: %ld, known: %ld, myxact: %ld, latest: %ld, mainxid: %ld, childxid: %ld, nooflo: %ld, slow: %ld\n",
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xc_by_recent_xmin,
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xc_by_known_xact,
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xc_by_my_xact,
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xc_by_latest_xid,
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xc_by_main_xid,
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@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/access/transam.h,v 1.64 2008/01/01 19:45:56 momjian Exp $
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* $PostgreSQL: pgsql/src/include/access/transam.h,v 1.65 2008/03/11 20:20:35 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -138,6 +138,7 @@ extern VariableCache ShmemVariableCache;
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*/
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extern bool TransactionIdDidCommit(TransactionId transactionId);
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extern bool TransactionIdDidAbort(TransactionId transactionId);
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extern bool TransactionIdIsKnownCompleted(TransactionId transactionId);
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extern void TransactionIdCommit(TransactionId transactionId);
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extern void TransactionIdAsyncCommit(TransactionId transactionId, XLogRecPtr lsn);
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extern void TransactionIdAbort(TransactionId transactionId);
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