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Commit83cd2d8

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committed
Make heap_fetch API more consistent by having the buffer remain pinned
in all cases when keep_buf = true. This allows ANALYZE's inner loop touse heap_release_fetch, which saves multiple buffer lookups for the samepage and avoids overestimation of cost by the vacuum cost mechanism.
1 parent2c66dcf commit83cd2d8

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3 files changed

+31
-28
lines changed

3 files changed

+31
-28
lines changed

‎src/backend/access/heap/heapam.c

Lines changed: 23 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.179 2004/10/15 22:39:42 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.180 2004/10/26 16:05:02 tgl Exp $
1212
*
1313
*
1414
* INTERFACE ROUTINES
@@ -878,14 +878,16 @@ heap_getnext(HeapScanDesc scan, ScanDirection direction)
878878
* is set to the buffer holding the tuple and TRUE is returned. The caller
879879
* must unpin the buffer when done with the tuple.
880880
*
881-
* If the tuple is not found, then tuple->t_data is set to NULL, *userbuf
882-
* is set toInvalidBuffer, and FALSE is returned.
881+
* If the tuple is not found (ie, item number references a deleted slot),
882+
*then tuple->t_datais set toNULL and FALSE is returned.
883883
*
884-
* If the tuple is found but fails the time qual check, then FALSE will be
885-
* returned. When the caller specifies keep_buf = true, we retain the pin
886-
* on the buffer and return it in *userbuf (so the caller can still access
887-
* the tuple); when keep_buf = false, the pin is released and *userbuf is set
888-
* to InvalidBuffer.
884+
* If the tuple is found but fails the time qual check, then FALSE is returned
885+
* but tuple->t_data is left pointing to the tuple.
886+
*
887+
* keep_buf determines what is done with the buffer in the FALSE-result cases.
888+
* When the caller specifies keep_buf = true, we retain the pin on the buffer
889+
* and return it in *userbuf (so the caller must eventually unpin it); when
890+
* keep_buf = false, the pin is released and *userbuf is set to InvalidBuffer.
889891
*
890892
* It is somewhat inconsistent that we ereport() on invalid block number but
891893
* return false on invalid item number. This is historical. The only
@@ -914,6 +916,8 @@ heap_fetch(Relation relation,
914916
* InvalidBuffer on entry, that buffer will be released before reading
915917
* the new page. This saves a separate ReleaseBuffer step and hence
916918
* one entry into the bufmgr when looping through multiple fetches.
919+
* Also, if *userbuf is the same buffer that holds the target tuple,
920+
* we avoid bufmgr manipulation altogether.
917921
*/
918922
bool
919923
heap_release_fetch(Relationrelation,
@@ -962,8 +966,13 @@ heap_release_fetch(Relation relation,
962966
if (!ItemIdIsUsed(lp))
963967
{
964968
LockBuffer(buffer,BUFFER_LOCK_UNLOCK);
965-
ReleaseBuffer(buffer);
966-
*userbuf=InvalidBuffer;
969+
if (keep_buf)
970+
*userbuf=buffer;
971+
else
972+
{
973+
ReleaseBuffer(buffer);
974+
*userbuf=InvalidBuffer;
975+
}
967976
tuple->t_datamcxt=NULL;
968977
tuple->t_data=NULL;
969978
return false;
@@ -1007,17 +1016,13 @@ heap_release_fetch(Relation relation,
10071016

10081017
/* Tuple failed time qual, but maybe caller wants to see it anyway. */
10091018
if (keep_buf)
1010-
{
10111019
*userbuf=buffer;
1012-
1013-
return false;
1020+
else
1021+
{
1022+
ReleaseBuffer(buffer);
1023+
*userbuf=InvalidBuffer;
10141024
}
10151025

1016-
/* Okay to release pin on buffer. */
1017-
ReleaseBuffer(buffer);
1018-
1019-
*userbuf=InvalidBuffer;
1020-
10211026
return false;
10221027
}
10231028

‎src/backend/access/nbtree/nbtinsert.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.117 2004/10/15 22:39:49 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.118 2004/10/26 16:05:02 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -269,8 +269,8 @@ _bt_check_unique(Relation rel, BTItem btitem, Relation heapRel,
269269
SetBufferCommitInfoNeedsSave(buf);
270270
}
271271
LockBuffer(hbuffer,BUFFER_LOCK_UNLOCK);
272-
ReleaseBuffer(hbuffer);
273272
}
273+
ReleaseBuffer(hbuffer);
274274
}
275275
}
276276

‎src/backend/commands/analyze.c

Lines changed: 6 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.77 2004/09/30 23:21:19 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.78 2004/10/26 16:05:03 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -822,11 +822,12 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
822822
for (targoffset=FirstOffsetNumber;targoffset <=maxoffset;targoffset++)
823823
{
824824
HeapTupleDatatargtuple;
825-
Buffertupbuffer;
826825

827826
ItemPointerSet(&targtuple.t_self,targblock,targoffset);
828-
if (heap_fetch(onerel,SnapshotNow,&targtuple,&tupbuffer,
829-
false,NULL))
827+
/* We use heap_release_fetch to avoid useless bufmgr traffic */
828+
if (heap_release_fetch(onerel,SnapshotNow,
829+
&targtuple,&targbuffer,
830+
true,NULL))
830831
{
831832
/*
832833
* The first targrows live rows are simply copied into the
@@ -869,9 +870,6 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
869870
rowstoskip-=1;
870871
}
871872

872-
/* must release the extra pin acquired by heap_fetch */
873-
ReleaseBuffer(tupbuffer);
874-
875873
liverows+=1;
876874
}
877875
else
@@ -886,7 +884,7 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
886884
}
887885
}
888886

889-
/* Now release theinitialpin on the page */
887+
/* Now release the pin on the page */
890888
ReleaseBuffer(targbuffer);
891889
}
892890

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