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Teach heapam code to know the difference between a real seqscan and the

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pseudo HeapScanDesc created for a bitmap heap scan.  This avoids some useless
overhead during a bitmap scan startup, in particular invoking the syncscan
code.  (We might someday want to do that, but right now it's merely useless
contention for shared memory, to say nothing of possibly pushing useful
entries out of syncscan's small LRU list.)  This also allows elimination of
ugly pgstat_discount_heap_scan() kluge.
This commit is contained in:
Tom Lane
2007-06-09 18:49:55 +00:00
parent 7063c46fc1
commit 85d72f0516
5 changed files with 48 additions and 34 deletions
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4
src/include/access/heapam.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/access/heapam.h,v 1.125 2007/06/08 18:23:53 tgl Exp $
* $PostgreSQL: pgsql/src/include/access/heapam.h,v 1.126 2007/06/09 18:49:55 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -141,6 +141,8 @@ extern Relation heap_openrv(const RangeVar *relation, LOCKMODE lockmode);
extern HeapScanDesc heap_beginscan(Relation relation, Snapshot snapshot,
int nkeys, ScanKey key);
extern HeapScanDesc heap_beginscan_bm(Relation relation, Snapshot snapshot,
int nkeys, ScanKey key);
extern void heap_rescan(HeapScanDesc scan, ScanKey key);
extern void heap_endscan(HeapScanDesc scan);
extern HeapTuple heap_getnext(HeapScanDesc scan, ScanDirection direction);

7
src/include/access/relscan.h
View File

@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/access/relscan.h,v 1.55 2007/06/08 18:23:53 tgl Exp $
* $PostgreSQL: pgsql/src/include/access/relscan.h,v 1.56 2007/06/09 18:49:55 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -26,12 +26,13 @@ typedef struct HeapScanDescData
Snapshot rs_snapshot; /* snapshot to see */
int rs_nkeys; /* number of scan keys */
ScanKey rs_key; /* array of scan key descriptors */
bool rs_bitmapscan; /* true if this is really a bitmap scan */
bool rs_pageatatime; /* verify visibility page-at-a-time? */
/* state set up at initscan time */
BlockNumber rs_nblocks; /* number of blocks to scan */
BlockNumber rs_startblock; /* block # to start at */
BufferAccessStrategy rs_strategy; /* access strategy for reads */
bool rs_pageatatime; /* verify visibility page-at-a-time? */
bool rs_syncscan; /* report location to syncscan logic? */
/* scan current state */
@@ -42,7 +43,7 @@ typedef struct HeapScanDescData
/* NB: if rs_cbuf is not InvalidBuffer, we hold a pin on that buffer */
ItemPointerData rs_mctid; /* marked scan position, if any */
/* these fields only used in page-at-a-time mode */
/* these fields only used in page-at-a-time mode and for bitmap scans */
int rs_cindex; /* current tuple's index in vistuples */
int rs_mindex; /* marked tuple's saved index */
int rs_ntuples; /* number of visible tuples on page */