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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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22
src/backend/access/transam/xact.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.97 2001/02/18 04:50:43 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.98 2001/02/26 00:50:07 tgl Exp $
*
* NOTES
* Transaction aborts can now occur two ways:
@ -157,6 +157,7 @@
#include <sys/time.h>
#include "access/nbtree.h"
#include "access/xact.h"
#include "catalog/heap.h"
#include "catalog/index.h"
#include "commands/async.h"
@ -177,8 +178,6 @@
extern bool SharedBufferChanged;
void RecordTransactionCommit(void);
static void AbortTransaction(void);
static void AtAbort_Cache(void);
static void AtAbort_Locks(void);
@ -216,12 +215,14 @@ TransactionStateData CurrentTransactionStateData = {
TransactionState CurrentTransactionState = &CurrentTransactionStateData;
/*
* User-tweakable parameters
*/
int DefaultXactIsoLevel = XACT_READ_COMMITTED;
int XactIsoLevel;
#include "access/xlogutils.h"
int CommitDelay = 0; /* in microseconds */
int CommitDelay = 0; /* precommit delay in microseconds */
int CommitSiblings = 5; /* number of concurrent xacts needed to sleep */
static void (*_RollbackFunc)(void*) = NULL;
static void *_RollbackData = NULL;
@ -687,10 +688,15 @@ RecordTransactionCommit()
* Sleep before commit! So we can flush more than one
* commit records per single fsync. (The idea is some other
* backend may do the XLogFlush while we're sleeping. This
* needs work however, because on most Unixen, the minimum
* needs work still, because on most Unixen, the minimum
* select() delay is 10msec or more, which is way too long.)
*
* We do not sleep if enableFsync is not turned on, nor if there
* are fewer than CommitSiblings other backends with active
* transactions.
*/
if (CommitDelay > 0)
if (CommitDelay > 0 && enableFsync &&
CountActiveBackends() >= CommitSiblings)
{
struct timeval delay;