diff options
| author | Tom Lane | 2009-06-10 18:54:16 +0000 |
|---|---|---|
| committer | Tom Lane | 2009-06-10 18:54:16 +0000 |
| commit | 51ec830b663b4b8466bbc4bdf2511cd7dc3de35b (patch) | |
| tree | 03cc15a522348b60c0db1ce3bfa02efa1006d686 | |
| parent | e66b2519e2b6fbd82b6eb4f9ebf2aad30a4c5a22 (diff) | |
Keep rs_startblock the same during heap_rescan, so that a rescan of a SeqScan
node starts from the same place as the first scan did. This avoids surprising
behavior of scrollable and WITH HOLD cursors, as seen in Mark Kirkwood's bug
report of yesterday.
It's not entirely clear whether a rescan should be forced to drop out of the
syncscan mode, but for the moment I left the code behaving the same on that
point. Any change there would only be a performance and not a correctness
issue, anyway.
Back-patch to 8.3, since the unstable behavior was created by the syncscan
patch.
| -rw-r--r-- | src/backend/access/heap/heapam.c | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index ad11770aec..9973829654 100644 --- a/src/backend/access/heap/heapam.c +++ b/src/backend/access/heap/heapam.c @@ -93,7 +93,7 @@ static bool HeapSatisfiesHOTUpdate(Relation relation, Bitmapset *hot_attrs, * ---------------- */ static void -initscan(HeapScanDesc scan, ScanKey key) +initscan(HeapScanDesc scan, ScanKey key, bool is_rescan) { bool allow_strat; bool allow_sync; @@ -143,7 +143,16 @@ initscan(HeapScanDesc scan, ScanKey key) scan->rs_strategy = NULL; } - if (allow_sync && synchronize_seqscans) + if (is_rescan) + { + /* + * If rescan, keep the previous startblock setting so that rewinding + * a cursor doesn't generate surprising results. Reset the syncscan + * setting, though. + */ + scan->rs_syncscan = (allow_sync && synchronize_seqscans); + } + else if (allow_sync && synchronize_seqscans) { scan->rs_syncscan = true; scan->rs_startblock = ss_get_location(scan->rs_rd, scan->rs_nblocks); @@ -1218,7 +1227,7 @@ heap_beginscan_internal(Relation relation, Snapshot snapshot, else scan->rs_key = NULL; - initscan(scan, key); + initscan(scan, key, false); return scan; } @@ -1240,7 +1249,7 @@ heap_rescan(HeapScanDesc scan, /* * reinitialize scan descriptor */ - initscan(scan, key); + initscan(scan, key, true); } /* ---------------- |