From 6a4b0a82fa2f151eca9c45613e697298e131b41b Mon Sep 17 00:00:00 2001 From: tgl Date: Wed, 10 Jun 2009 18:54:16 +0000 Subject: [PATCH] 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. --- src/backend/access/heap/heapam.c | 17 +++++++++++++---- 1 file 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); } /* ---------------- -- 2.11.4.GIT