diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index cd4637db4b3ebd56d439b15d3ac616fca5326900..7134581333a6b550881c565b738b5b9e45ba5b13 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.247 2008/01/01 19:45:46 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.248 2008/01/14 01:39:09 tgl Exp $
*
*
* INTERFACE ROUTINES
@@ -62,6 +62,7 @@
static HeapScanDesc heap_beginscan_internal(Relation relation,
Snapshot snapshot,
int nkeys, ScanKey key,
+ bool allow_strat, bool allow_sync,
bool is_bitmapscan);
static XLogRecPtr log_heap_update(Relation reln, Buffer oldbuf,
ItemPointerData from, Buffer newbuf, HeapTuple newtup, bool move);
@@ -81,6 +82,9 @@ static bool HeapSatisfiesHOTUpdate(Relation relation, Bitmapset *hot_attrs,
static void
initscan(HeapScanDesc scan, ScanKey key)
{
+ bool allow_strat;
+ bool allow_sync;
+
/*
* Determine the number of blocks we have to scan.
*
@@ -99,25 +103,39 @@ initscan(HeapScanDesc scan, ScanKey key)
* strategy and enable synchronized scanning (see syncscan.c). Although
* the thresholds for these features could be different, we make them the
* same so that there are only two behaviors to tune rather than four.
+ * (However, some callers need to be able to disable one or both of
+ * these behaviors, independently of the size of the table.)
*
* During a rescan, don't make a new strategy object if we don't have to.
*/
- if (!scan->rs_bitmapscan &&
- !scan->rs_rd->rd_istemp &&
+ if (!scan->rs_rd->rd_istemp &&
scan->rs_nblocks > NBuffers / 4)
+ {
+ allow_strat = scan->rs_allow_strat;
+ allow_sync = scan->rs_allow_sync;
+ }
+ else
+ allow_strat = allow_sync = false;
+
+ if (allow_strat)
{
if (scan->rs_strategy == NULL)
scan->rs_strategy = GetAccessStrategy(BAS_BULKREAD);
-
- scan->rs_syncscan = true;
- scan->rs_startblock = ss_get_location(scan->rs_rd, scan->rs_nblocks);
}
else
{
if (scan->rs_strategy != NULL)
FreeAccessStrategy(scan->rs_strategy);
scan->rs_strategy = NULL;
+ }
+ if (allow_sync)
+ {
+ scan->rs_syncscan = true;
+ scan->rs_startblock = ss_get_location(scan->rs_rd, scan->rs_nblocks);
+ }
+ else
+ {
scan->rs_syncscan = false;
scan->rs_startblock = 0;
}
@@ -1058,29 +1076,47 @@ heap_openrv(const RangeVar *relation, LOCKMODE lockmode)
/* ----------------
* heap_beginscan - begin relation scan
*
- * heap_beginscan_bm is an alternative entry point for setting up a HeapScanDesc
- * for a bitmap heap scan. Although that scan technology is really quite
- * unlike a standard seqscan, there is just enough commonality to make it
- * worth using the same data structure.
+ * heap_beginscan_strat offers an extended API that lets the caller control
+ * whether a nondefault buffer access strategy can be used, and whether
+ * syncscan can be chosen (possibly resulting in the scan not starting from
+ * block zero). Both of these default to TRUE with plain heap_beginscan.
+ *
+ * heap_beginscan_bm is an alternative entry point for setting up a
+ * HeapScanDesc for a bitmap heap scan. Although that scan technology is
+ * really quite unlike a standard seqscan, there is just enough commonality
+ * to make it worth using the same data structure.
* ----------------
*/
HeapScanDesc
heap_beginscan(Relation relation, Snapshot snapshot,
int nkeys, ScanKey key)
{
- return heap_beginscan_internal(relation, snapshot, nkeys, key, false);
+ return heap_beginscan_internal(relation, snapshot, nkeys, key,
+ true, true, false);
+}
+
+HeapScanDesc
+heap_beginscan_strat(Relation relation, Snapshot snapshot,
+ int nkeys, ScanKey key,
+ bool allow_strat, bool allow_sync)
+{
+ return heap_beginscan_internal(relation, snapshot, nkeys, key,
+ allow_strat, allow_sync, false);
}
HeapScanDesc
heap_beginscan_bm(Relation relation, Snapshot snapshot,
int nkeys, ScanKey key)
{
- return heap_beginscan_internal(relation, snapshot, nkeys, key, true);
+ return heap_beginscan_internal(relation, snapshot, nkeys, key,
+ false, false, true);
}
static HeapScanDesc
heap_beginscan_internal(Relation relation, Snapshot snapshot,
- int nkeys, ScanKey key, bool is_bitmapscan)
+ int nkeys, ScanKey key,
+ bool allow_strat, bool allow_sync,
+ bool is_bitmapscan)
{
HeapScanDesc scan;
@@ -1103,6 +1139,8 @@ heap_beginscan_internal(Relation relation, Snapshot snapshot,
scan->rs_nkeys = nkeys;
scan->rs_bitmapscan = is_bitmapscan;
scan->rs_strategy = NULL; /* set in initscan */
+ scan->rs_allow_strat = allow_strat;
+ scan->rs_allow_sync = allow_sync;
/*
* we can use page-at-a-time mode if it's an MVCC-safe snapshot
diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 97904b703cfc6235f1508c895552bed05043416f..a8200b105e456c5fc7bc51fa94b603d54f6a50a0 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.290 2008/01/03 21:23:15 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.291 2008/01/14 01:39:09 tgl Exp $
*
*
* INTERFACE ROUTINES
@@ -2004,12 +2004,16 @@ validate_index_heapscan(Relation heapRelation,
/*
* Prepare for scan of the base relation. We need just those tuples
- * satisfying the passed-in reference snapshot.
- */
- scan = heap_beginscan(heapRelation, /* relation */
- snapshot, /* seeself */
- 0, /* number of keys */
- NULL); /* scan key */
+ * satisfying the passed-in reference snapshot. We must disable syncscan
+ * here, because it's critical that we read from block zero forward to
+ * match the sorted TIDs.
+ */
+ scan = heap_beginscan_strat(heapRelation, /* relation */
+ snapshot, /* snapshot */
+ 0, /* number of keys */
+ NULL, /* scan key */
+ true, /* buffer access strategy OK */
+ false); /* syncscan not OK */
/*
* Scan all tuples matching the snapshot.
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index 8052e49f30b30970a74a1f8a09f96998090b70e3..78eca9533f773eb557caf36198937c0083ae5eb4 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/include/access/heapam.h,v 1.129 2008/01/01 19:45:56 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/access/heapam.h,v 1.130 2008/01/14 01:39:09 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -141,6 +141,9 @@ 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_strat(Relation relation, Snapshot snapshot,
+ int nkeys, ScanKey key,
+ bool allow_strat, bool allow_sync);
extern HeapScanDesc heap_beginscan_bm(Relation relation, Snapshot snapshot,
int nkeys, ScanKey key);
extern void heap_rescan(HeapScanDesc scan, ScanKey key);
diff --git a/src/include/access/relscan.h b/src/include/access/relscan.h
index 87d8123ba6a43f0e6204d649e4be4201ee2a5f9c..62a0276fd06f6b1176e5d398d8ad82432b5d643c 100644
--- a/src/include/access/relscan.h
+++ b/src/include/access/relscan.h
@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/include/access/relscan.h,v 1.59 2008/01/01 19:45:56 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/access/relscan.h,v 1.60 2008/01/14 01:39:09 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -28,6 +28,8 @@ typedef struct HeapScanDescData
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? */
+ bool rs_allow_strat; /* allow or disallow use of access strategy */
+ bool rs_allow_sync; /* allow or disallow use of syncscan */
/* state set up at initscan time */
BlockNumber rs_nblocks; /* number of blocks to scan */