diff options
Diffstat (limited to 'src/backend/access/heap/heapam.c')
| -rw-r--r-- | src/backend/access/heap/heapam.c | 61 |
1 files changed, 48 insertions, 13 deletions
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index 6f4ff2718fe..050efdc4806 100644 --- a/src/backend/access/heap/heapam.c +++ b/src/backend/access/heap/heapam.c @@ -80,8 +80,11 @@ bool synchronize_seqscans = true; static HeapScanDesc heap_beginscan_internal(Relation relation, Snapshot snapshot, int nkeys, ScanKey key, - bool allow_strat, bool allow_sync, bool allow_pagemode, - bool is_bitmapscan, bool is_samplescan, + bool allow_strat, + bool allow_sync, + bool allow_pagemode, + bool is_bitmapscan, + bool is_samplescan, bool temp_snap); static HeapTuple heap_prepare_insert(Relation relation, HeapTuple tup, TransactionId xid, CommandId cid, int options); @@ -207,7 +210,7 @@ static const int MultiXactStatusLock[MaxMultiXactStatus + 1] = * ---------------- */ static void -initscan(HeapScanDesc scan, ScanKey key, bool is_rescan) +initscan(HeapScanDesc scan, ScanKey key, bool keep_startblock) { bool allow_strat; bool allow_sync; @@ -257,12 +260,12 @@ initscan(HeapScanDesc scan, ScanKey key, bool is_rescan) scan->rs_strategy = NULL; } - if (is_rescan) + if (keep_startblock) { /* - * If rescan, keep the previous startblock setting so that rewinding a - * cursor doesn't generate surprising results. Reset the syncscan - * setting, though. + * When rescanning, we want to keep the previous startblock setting, + * so that rewinding a cursor doesn't generate surprising results. + * Reset the active syncscan setting, though. */ scan->rs_syncscan = (allow_sync && synchronize_seqscans); } @@ -1313,6 +1316,10 @@ heap_openrv_extended(const RangeVar *relation, LOCKMODE lockmode, /* ---------------- * heap_beginscan - begin relation scan * + * heap_beginscan is the "standard" case. + * + * heap_beginscan_catalog differs in setting up its own temporary snapshot. + * * 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 @@ -1323,8 +1330,11 @@ heap_openrv_extended(const RangeVar *relation, LOCKMODE lockmode, * really quite unlike a standard seqscan, there is just enough commonality * to make it worth using the same data structure. * - * heap_beginscan_samplingscan is alternate entry point for setting up a - * HeapScanDesc for a TABLESAMPLE scan. + * heap_beginscan_sampling is an alternative entry point for setting up a + * HeapScanDesc for a TABLESAMPLE scan. As with bitmap scans, it's worth + * using the same data structure although the behavior is rather different. + * In addition to the options offered by heap_beginscan_strat, this call + * also allows control of whether page-mode visibility checking is used. * ---------------- */ HeapScanDesc @@ -1366,18 +1376,22 @@ heap_beginscan_bm(Relation relation, Snapshot snapshot, HeapScanDesc heap_beginscan_sampling(Relation relation, Snapshot snapshot, int nkeys, ScanKey key, - bool allow_strat, bool allow_pagemode) + bool allow_strat, bool allow_sync, bool allow_pagemode) { return heap_beginscan_internal(relation, snapshot, nkeys, key, - allow_strat, false, allow_pagemode, + allow_strat, allow_sync, allow_pagemode, false, true, false); } static HeapScanDesc heap_beginscan_internal(Relation relation, Snapshot snapshot, int nkeys, ScanKey key, - bool allow_strat, bool allow_sync, bool allow_pagemode, - bool is_bitmapscan, bool is_samplescan, bool temp_snap) + bool allow_strat, + bool allow_sync, + bool allow_pagemode, + bool is_bitmapscan, + bool is_samplescan, + bool temp_snap) { HeapScanDesc scan; @@ -1462,6 +1476,27 @@ heap_rescan(HeapScanDesc scan, } /* ---------------- + * heap_rescan_set_params - restart a relation scan after changing params + * + * This call allows changing the buffer strategy, syncscan, and pagemode + * options before starting a fresh scan. Note that although the actual use + * of syncscan might change (effectively, enabling or disabling reporting), + * the previously selected startblock will be kept. + * ---------------- + */ +void +heap_rescan_set_params(HeapScanDesc scan, ScanKey key, + bool allow_strat, bool allow_sync, bool allow_pagemode) +{ + /* adjust parameters */ + scan->rs_allow_strat = allow_strat; + scan->rs_allow_sync = allow_sync; + scan->rs_pageatatime = allow_pagemode && IsMVCCSnapshot(scan->rs_snapshot); + /* ... and rescan */ + heap_rescan(scan, key); +} + +/* ---------------- * heap_endscan - end relation scan * * See how to integrate with index scans. |