diff options
Diffstat (limited to 'src/backend/access/heap/heapam.c')
| -rw-r--r-- | src/backend/access/heap/heapam.c | 64 |
1 files changed, 51 insertions, 13 deletions
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index cd4637db4b3..7134581333a 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 |