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Implement COMMIT_SIBLINGS parameter to allow pre-commit delay to occur

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only if at least N other backends currently have open transactions.  This
is not a great deal of intelligence about whether a delay might be
profitable ... but it beats no intelligence at all.  Note that the default
COMMIT_DELAY is still zero --- this new code does nothing unless that
setting is changed.
Also, mark ENABLEFSYNC as a system-wide setting.  It's no longer safe to
allow that to be set per-backend, since we may be relying on some other
backend's fsync to have synced the WAL log.
This commit is contained in:
Tom Lane
2001-02-26 00:50:08 +00:00
parent 60774e8210
commit 9c9936587c
10 changed files with 94 additions and 31 deletions
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53
src/backend/storage/ipc/sinval.c
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@@ -8,16 +8,14 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.25 2001/01/24 19:43:07 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.26 2001/02/26 00:50:07 tgl Exp $
*
*-------------------------------------------------------------------------
*/
/* #define INVALIDDEBUG 1 */
#include "postgres.h"
#include <sys/types.h>
#include "postgres.h"
#include "storage/backendid.h"
#include "storage/proc.h"
#include "storage/sinval.h"
@@ -347,11 +345,54 @@ GetSnapshotData(bool serializable)
return snapshot;
}
/*
* CountActiveBackends --- count backends (other than myself) that are in
* active transactions. This is used as a heuristic to decide if
* a pre-XLOG-flush delay is worthwhile during commit.
*
* An active transaction is something that has written at least one XLOG
* record; read-only transactions don't count. Also, do not count backends
* that are blocked waiting for locks, since they are not going to get to
* run until someone else commits.
*/
int
CountActiveBackends(void)
{
SISeg *segP = shmInvalBuffer;
ProcState *stateP = segP->procState;
int count = 0;
int index;
/*
* Note: for speed, we don't acquire SInvalLock. This is a little bit
* bogus, but since we are only testing xrecoff for zero or nonzero,
* it should be OK. The result is only used for heuristic purposes
* anyway...
*/
for (index = 0; index < segP->lastBackend; index++)
{
SHMEM_OFFSET pOffset = stateP[index].procStruct;
if (pOffset != INVALID_OFFSET)
{
PROC *proc = (PROC *) MAKE_PTR(pOffset);
if (proc == MyProc)
continue; /* do not count myself */
if (proc->logRec.xrecoff == 0)
continue; /* do not count if not in a transaction */
if (proc->waitLock != NULL)
continue; /* do not count if blocked on a lock */
count++;
}
}
return count;
}
/*
* GetUndoRecPtr -- returns oldest PROC->logRec.
*/
XLogRecPtr GetUndoRecPtr(void);
XLogRecPtr
GetUndoRecPtr(void)
{