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Commit49f68a8

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committed
Avoid disk writes for read-only transactions.
1 parentcffd0f9 commit49f68a8

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2 files changed

+49
-29
lines changed

2 files changed

+49
-29
lines changed

‎src/backend/access/transam/xact.c

Lines changed: 33 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
*
88
*
99
* IDENTIFICATION
10-
* $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.41 1999/06/10 14:17:06 vadim Exp $
10+
* $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.42 1999/06/29 04:54:46 vadim Exp $
1111
*
1212
* NOTES
1313
*Transaction aborts can now occur two ways:
@@ -158,6 +158,8 @@
158158
#include<commands/sequence.h>
159159
#include<libpq/be-fsstubs.h>
160160

161+
externboolSharedBufferChanged;
162+
161163
staticvoidAbortTransaction(void);
162164
staticvoidAtAbort_Cache(void);
163165
staticvoidAtAbort_Locks(void);
@@ -618,30 +620,36 @@ RecordTransactionCommit()
618620
*/
619621
xid=GetCurrentTransactionId();
620622

621-
/*----------------
623+
/*
622624
*flush the buffer manager pages. Note: if we have stable
623625
*main memory, dirty shared buffers are not flushed
624626
*plai 8/7/90
625-
* ----------------
626627
*/
627628
leak=BufferPoolCheckLeak();
628-
FlushBufferPool(!TransactionFlushEnabled());
629-
if (leak)
630-
ResetBufferPool();
631629

632-
/* ----------------
633-
*have the transaction access methods record the status
634-
*of this transaction id in the pg_log / pg_time relations.
635-
* ----------------
630+
/*
631+
* If no one shared buffer was changed by this transaction then
632+
* we don't flush shared buffers and don't record commit status.
636633
*/
637-
TransactionIdCommit(xid);
634+
if (SharedBufferChanged)
635+
{
636+
FlushBufferPool(!TransactionFlushEnabled());
637+
if (leak)
638+
ResetBufferPool();
639+
640+
/*
641+
*have the transaction access methods record the status
642+
*of this transaction id in the pg_log relation.
643+
*/
644+
TransactionIdCommit(xid);
645+
646+
/*
647+
*Now write the log info to the disk too.
648+
*/
649+
leak=BufferPoolCheckLeak();
650+
FlushBufferPool(!TransactionFlushEnabled());
651+
}
638652

639-
/* ----------------
640-
*Now write the log/time info to the disk too.
641-
* ----------------
642-
*/
643-
leak=BufferPoolCheckLeak();
644-
FlushBufferPool(!TransactionFlushEnabled());
645653
if (leak)
646654
ResetBufferPool();
647655
}
@@ -731,19 +739,14 @@ RecordTransactionAbort()
731739
*/
732740
xid=GetCurrentTransactionId();
733741

734-
/*----------------
735-
*havethe transaction access methods record the status
736-
*of this transaction id in the pg_log/ pg_time relations.
737-
*----------------
742+
/*
743+
* Havethe transaction access methods record the status of
744+
* this transaction id in the pg_logrelation. We skip it
745+
*if no one shared buffer was changed by this transaction.
738746
*/
739-
TransactionIdAbort(xid);
747+
if (SharedBufferChanged)
748+
TransactionIdAbort(xid);
740749

741-
/* ----------------
742-
*flush the buffer manager pages. Note: if we have stable
743-
*main memory, dirty shared buffers are not flushed
744-
*plai 8/7/90
745-
* ----------------
746-
*/
747750
ResetBufferPool();
748751
}
749752

@@ -965,6 +968,7 @@ CommitTransaction()
965968
* ----------------
966969
*/
967970
s->state=TRANS_DEFAULT;
971+
SharedBufferChanged= false;/* safest place to do it */
968972

969973
}
970974

@@ -1028,6 +1032,7 @@ AbortTransaction()
10281032
* ----------------
10291033
*/
10301034
s->state=TRANS_DEFAULT;
1035+
SharedBufferChanged= false;/* safest place to do it */
10311036
}
10321037

10331038
/* --------------------------------

‎src/backend/storage/buffer/bufmgr.c

Lines changed: 16 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
*
88
*
99
* IDENTIFICATION
10-
* $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.55 1999/06/11 09:00:02 vadim Exp $
10+
* $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.56 1999/06/29 04:54:47 vadim Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -78,6 +78,15 @@ extern long int LocalBufferHitCount;
7878
externlongintBufferFlushCount;
7979
externlongintLocalBufferFlushCount;
8080

81+
/*
82+
* It's used to avoid disk writes for read-only transactions
83+
* (i.e. when no one shared buffer was changed by transaction).
84+
* We set it to true in WriteBuffer/WriteNoReleaseBuffer when
85+
* marking shared buffer as dirty. We set it to false in xact.c
86+
* after transaction is committed/aborted.
87+
*/
88+
boolSharedBufferChanged= false;
89+
8190
staticintWriteMode=BUFFER_LATE_WRITE;/* Delayed write is
8291
* default */
8392

@@ -699,6 +708,8 @@ WriteBuffer(Buffer buffer)
699708

700709
bufHdr=&BufferDescriptors[buffer-1];
701710

711+
SharedBufferChanged= true;
712+
702713
SpinAcquire(BufMgrLock);
703714
Assert(bufHdr->refcount>0);
704715
bufHdr->flags |= (BM_DIRTY |BM_JUST_DIRTIED);
@@ -810,6 +821,8 @@ FlushBuffer(Buffer buffer, bool release)
810821
bufrel=RelationIdCacheGetRelation(bufHdr->tag.relId.relId);
811822
Assert(bufrel!= (Relation)NULL);
812823

824+
SharedBufferChanged= true;
825+
813826
/* To check if block content changed while flushing. - vadim 01/17/97 */
814827
SpinAcquire(BufMgrLock);
815828
bufHdr->flags &= ~BM_JUST_DIRTIED;
@@ -875,6 +888,8 @@ WriteNoReleaseBuffer(Buffer buffer)
875888

876889
bufHdr=&BufferDescriptors[buffer-1];
877890

891+
SharedBufferChanged= true;
892+
878893
SpinAcquire(BufMgrLock);
879894
bufHdr->flags |= (BM_DIRTY |BM_JUST_DIRTIED);
880895
SpinRelease(BufMgrLock);

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