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authorNoah Misch <noah@leadboat.com>2017-11-05 09:25:52 -0800
committerNoah Misch <noah@leadboat.com>2017-11-05 09:25:59 -0800
commit2168f37c4db65f40925f4f8ccbb901544a5edb84 (patch)
tree1ad910891a984e24d8d097720be74f65c788700c /src/backend/commands/copy.c
parentc3f43a71663cdb9d589f536b544b03675f13e14f (diff)
downloadpostgresql-2168f37c4db65f40925f4f8ccbb901544a5edb84.tar.gz
postgresql-2168f37c4db65f40925f4f8ccbb901544a5edb84.zip
Ignore CatalogSnapshot when checking COPY FREEZE prerequisites.
This restores the ability, essentially lost in commit ffaa44cb559db332baeee7d25dedd74a61974203, to use COPY FREEZE under REPEATABLE READ isolation. Back-patch to 9.4, like that commit. Reviewed by Tom Lane. Discussion: https://postgr.es/m/CA+TgmoahWDm-7fperBxzU9uZ99LPMUmEpSXLTw9TmrOgzwnORw@mail.gmail.com
Diffstat (limited to 'src/backend/commands/copy.c')
-rw-r--r--src/backend/commands/copy.c18
1 files changed, 15 insertions, 3 deletions
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index ef81e3be711..ef301b6328a 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -2392,13 +2392,25 @@ CopyFrom(CopyState cstate)
/*
* Optimize if new relfilenode was created in this subxact or one of its
* committed children and we won't see those rows later as part of an
- * earlier scan or command. This ensures that if this subtransaction
- * aborts then the frozen rows won't be visible after xact cleanup. Note
+ * earlier scan or command. The subxact test ensures that if this subxact
+ * aborts then the frozen rows won't be visible after xact cleanup. Note
* that the stronger test of exactly which subtransaction created it is
- * crucial for correctness of this optimization.
+ * crucial for correctness of this optimization. The test for an earlier
+ * scan or command tolerates false negatives. FREEZE causes other sessions
+ * to see rows they would not see under MVCC, and a false negative merely
+ * spreads that anomaly to the current session.
*/
if (cstate->freeze)
{
+ /*
+ * Tolerate one registration for the benefit of FirstXactSnapshot.
+ * Scan-bearing queries generally create at least two registrations,
+ * though relying on that is fragile, as is ignoring ActiveSnapshot.
+ * Clear CatalogSnapshot to avoid counting its registration. We'll
+ * still detect ongoing catalog scans, each of which separately
+ * registers the snapshot it uses.
+ */
+ InvalidateCatalogSnapshot();
if (!ThereAreNoPriorRegisteredSnapshots() || !ThereAreNoReadyPortals())
ereport(ERROR,
(errcode(ERRCODE_INVALID_TRANSACTION_STATE),