From 2e44770fa39051f404f7d94fed557b359b1dba3c Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Mon, 22 Jul 2013 16:01:17 -0400 Subject: [PATCH] pgrowlocks: Use GetActiveSnapshot() rather than SnapshotNow. Per discussion, it's desirable to eliminate all remaining uses of SnapshotNow, because it has unpleasant semantics: race conditions can result in seeing multiple versions of a concurrently updated row, or none at all. By using GetActiveSnapshot() here, callers will see exactly those rows that would have been visible if the invoking query had scanned the table using, for example, a SELECT statement. This is slightly different from the old behavior, because commits that happen concurrently with the scan will not affect the results. In REPEATABLE READ or SERIALIZABLE modes, where transaction snapshots are used, commits that have happened since the start of the transaction will also not affect the results. It is hoped that this minor incompatibility will be thought an improvement, or at least no worse than what we did before. --- contrib/pgrowlocks/pgrowlocks.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/contrib/pgrowlocks/pgrowlocks.c b/contrib/pgrowlocks/pgrowlocks.c index 8d8e78ea4a..636ff05670 100644 --- a/contrib/pgrowlocks/pgrowlocks.c +++ b/contrib/pgrowlocks/pgrowlocks.c @@ -35,6 +35,7 @@ #include "utils/acl.h" #include "utils/builtins.h" #include "utils/rel.h" +#include "utils/snapmgr.h" #include "utils/tqual.h" @@ -106,7 +107,7 @@ pgrowlocks(PG_FUNCTION_ARGS) aclcheck_error(aclresult, ACL_KIND_CLASS, RelationGetRelationName(rel)); - scan = heap_beginscan(rel, SnapshotNow, 0, NULL); + scan = heap_beginscan(rel, GetActiveSnapshot(), 0, NULL); mydata = palloc(sizeof(*mydata)); mydata->rel = rel; mydata->scan = scan; -- 2.40.0