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Postgres FD Implementation
Commit 611b4393 authored by Tom Lane's avatar Tom Lane
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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.
parent ba8a9a92
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Showing with 67 additions and 32 deletions
src/backend/access/transam/transam.c
View file @ 611b4393
......@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.73 2008/01/01 19:45:48 momjian Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.74 2008/03/11 20:20:35 tgl Exp $
*
* NOTES
* This file contains the high level access-method interface to the
......@@ -25,12 +25,11 @@
#include "utils/tqual.h"
static XidStatus TransactionLogFetch(TransactionId transactionId);
static void TransactionLogUpdate(TransactionId transactionId,
XidStatus status, XLogRecPtr lsn);
/*
* Single-item cache for results of TransactionLogFetch.
* Single-item cache for results of TransactionLogFetch. It's worth having
* such a cache because we frequently find ourselves repeatedly checking the
* same XID, for example when scanning a table just after a bulk insert,
* update, or delete.
*/
static TransactionId cachedFetchXid = InvalidTransactionId;
static XidStatus cachedFetchXidStatus;
......@@ -39,9 +38,14 @@ static XLogRecPtr cachedCommitLSN;
/* Handy constant for an invalid xlog recptr */
static const XLogRecPtr InvalidXLogRecPtr = {0, 0};
/* Local functions */
static XidStatus TransactionLogFetch(TransactionId transactionId);
static void TransactionLogUpdate(TransactionId transactionId,
XidStatus status, XLogRecPtr lsn);
/* ----------------------------------------------------------------
* postgres log access method interface
* Postgres log access method interface
*
* TransactionLogFetch
* TransactionLogUpdate
......@@ -82,8 +86,8 @@ TransactionLogFetch(TransactionId transactionId)
xidstatus = TransactionIdGetStatus(transactionId, &xidlsn);
/*
* DO NOT cache status for unfinished or sub-committed transactions! We
* only cache status that is guaranteed not to change.
* Cache it, but DO NOT cache status for unfinished or sub-committed
* transactions! We only cache status that is guaranteed not to change.
*/
if (xidstatus != TRANSACTION_STATUS_IN_PROGRESS &&
xidstatus != TRANSACTION_STATUS_SUB_COMMITTED)
......@@ -96,12 +100,11 @@ TransactionLogFetch(TransactionId transactionId)
return xidstatus;
}
/* --------------------------------
/*
* TransactionLogUpdate
*
* Store the new status of a transaction. The commit record LSN must be
* passed when recording an async commit; else it should be InvalidXLogRecPtr.
* --------------------------------
*/
static inline void
TransactionLogUpdate(TransactionId transactionId,
......@@ -131,32 +134,27 @@ TransactionLogMultiUpdate(int nxids, TransactionId *xids,
TransactionIdSetStatus(xids[i], status, lsn);
}
/* ----------------------------------------------------------------
* Interface functions
*
* TransactionId DidCommit
* TransactionId DidAbort
* TransactionId IsInProgress
* TransactionIdDidCommit
* TransactionIdDidAbort
* ========
* these functions test the transaction status of
* a specified transaction id.
*
* TransactionId Commit
* TransactionId Abort
* TransactionIdCommit
* TransactionIdAbort
* ========
* these functions set the transaction status
* of the specified xid.
*
* See also TransactionIdIsInProgress, which once was in this module
* but now lives in procarray.c.
* ----------------------------------------------------------------
*/
/* --------------------------------
* TransactionId DidCommit
* TransactionId DidAbort
* TransactionId IsInProgress
* --------------------------------
*/
/*
* TransactionIdDidCommit
* True iff transaction associated with the identifier did commit.
......@@ -262,11 +260,33 @@ TransactionIdDidAbort(TransactionId transactionId)
return false;
}
/* --------------------------------
* TransactionId Commit
* TransactionId Abort
* --------------------------------
/*
* TransactionIdIsKnownCompleted
* True iff transaction associated with the identifier is currently
* known to have either committed or aborted.
*
* This does NOT look into pg_clog but merely probes our local cache
* (and so it's not named TransactionIdDidComplete, which would be the
* appropriate name for a function that worked that way). The intended
* use is just to short-circuit TransactionIdIsInProgress calls when doing
* repeated tqual.c checks for the same XID. If this isn't extremely fast
* then it will be counterproductive.
*
* Note:
* Assumes transaction identifier is valid.
*/
bool
TransactionIdIsKnownCompleted(TransactionId transactionId)
{
if (TransactionIdEquals(transactionId, cachedFetchXid))
{
/* If it's in the cache at all, it must be completed. */
return true;
}
return false;
}
/*
* TransactionIdCommit
......@@ -292,7 +312,6 @@ TransactionIdAsyncCommit(TransactionId transactionId, XLogRecPtr lsn)
TransactionLogUpdate(transactionId, TRANSACTION_STATUS_COMMITTED, lsn);
}
/*
* TransactionIdAbort
* Aborts the transaction associated with the identifier.
......@@ -352,7 +371,6 @@ TransactionIdAsyncCommitTree(int nxids, TransactionId *xids, XLogRecPtr lsn)
lsn);
}
/*
* TransactionIdAbortTree
* Marks all the given transaction ids as aborted.
......@@ -368,6 +386,7 @@ TransactionIdAbortTree(int nxids, TransactionId *xids)
InvalidXLogRecPtr);
}
/*
* TransactionIdPrecedes --- is id1 logically < id2?
*/
......
src/backend/storage/ipc/procarray.c
View file @ 611b4393
......@@ -23,7 +23,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.40 2008/01/09 21:52:36 tgl Exp $
* $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.41 2008/03/11 20:20:35 tgl Exp $
*
*-------------------------------------------------------------------------
*/
......@@ -60,6 +60,7 @@ static ProcArrayStruct *procArray;
/* counters for XidCache measurement */
static long xc_by_recent_xmin = 0;
static long xc_by_known_xact = 0;
static long xc_by_my_xact = 0;
static long xc_by_latest_xid = 0;
static long xc_by_main_xid = 0;
......@@ -68,6 +69,7 @@ static long xc_no_overflow = 0;
static long xc_slow_answer = 0;
#define xc_by_recent_xmin_inc() (xc_by_recent_xmin++)
#define xc_by_known_xact_inc() (xc_by_known_xact++)
#define xc_by_my_xact_inc() (xc_by_my_xact++)
#define xc_by_latest_xid_inc() (xc_by_latest_xid++)
#define xc_by_main_xid_inc() (xc_by_main_xid++)
......@@ -79,6 +81,7 @@ static void DisplayXidCache(void);
#else /* !XIDCACHE_DEBUG */
#define xc_by_recent_xmin_inc() ((void) 0)
#define xc_by_known_xact_inc() ((void) 0)
#define xc_by_my_xact_inc() ((void) 0)
#define xc_by_latest_xid_inc() ((void) 0)
#define xc_by_main_xid_inc() ((void) 0)
......@@ -353,6 +356,17 @@ TransactionIdIsInProgress(TransactionId xid)
return false;
}
/*
* We may have just checked the status of this transaction, so if it is
* already known to be completed, we can fall out without any access to
* shared memory.
*/
if (TransactionIdIsKnownCompleted(xid))
{
xc_by_known_xact_inc();
return false;
}
/*
* Also, we can handle our own transaction (and subtransactions) without
* any access to shared memory.
......@@ -1335,8 +1349,9 @@ static void
DisplayXidCache(void)
{
fprintf(stderr,
"XidCache: xmin: %ld, myxact: %ld, latest: %ld, mainxid: %ld, childxid: %ld, nooflo: %ld, slow: %ld\n",
"XidCache: xmin: %ld, known: %ld, myxact: %ld, latest: %ld, mainxid: %ld, childxid: %ld, nooflo: %ld, slow: %ld\n",
xc_by_recent_xmin,
xc_by_known_xact,
xc_by_my_xact,
xc_by_latest_xid,
xc_by_main_xid,
......
src/include/access/transam.h
View file @ 611b4393
......@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/access/transam.h,v 1.64 2008/01/01 19:45:56 momjian Exp $
* $PostgreSQL: pgsql/src/include/access/transam.h,v 1.65 2008/03/11 20:20:35 tgl Exp $
*
*-------------------------------------------------------------------------
*/
......@@ -138,6 +138,7 @@ extern VariableCache ShmemVariableCache;
*/
extern bool TransactionIdDidCommit(TransactionId transactionId);
extern bool TransactionIdDidAbort(TransactionId transactionId);
extern bool TransactionIdIsKnownCompleted(TransactionId transactionId);
extern void TransactionIdCommit(TransactionId transactionId);
extern void TransactionIdAsyncCommit(TransactionId transactionId, XLogRecPtr lsn);
extern void TransactionIdAbort(TransactionId transactionId);
......
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