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Revert patch for taking fewer snapshots.

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This reverts commit d573e239f0, "Take fewer
snapshots".  While that seemed like a good idea at the time, it caused
execution to use a snapshot that had been acquired before locking any of
the tables mentioned in the query.  This created user-visible anomalies
that were not present in any prior release of Postgres, as reported by
Tomas Vondra.  While this whole area could do with a redesign (since there
are related cases that have anomalies anyway), it doesn't seem likely that
any future patch would be reasonably back-patchable; and we don't want 9.2
to exhibit a behavior that's subtly unlike either past or future releases.
Hence, revert to prior code while we rethink the problem.
This commit is contained in:
Tom Lane
2012-11-26 15:55:51 -05:00
parent eea6ada926
commit 786afc1ce5
7 changed files with 32 additions and 46 deletions
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32
src/backend/tcop/postgres.c
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@ -974,6 +974,10 @@ exec_simple_query(const char *query_string)
plantree_list = pg_plan_queries(querytree_list, 0, NULL);
/* Done with the snapshot used for parsing/planning */
if (snapshot_set)
PopActiveSnapshot();
/* If we got a cancel signal in analysis or planning, quit */
CHECK_FOR_INTERRUPTS();
@ -998,19 +1002,9 @@ exec_simple_query(const char *query_string)
NULL);
/*
* Start the portal.
*
* If we took a snapshot for parsing/planning, the portal may be able
* to reuse it for the execution phase. Currently, this will only
* happen in PORTAL_ONE_SELECT mode. But even if PortalStart doesn't
* end up being able to do this, keeping the parse/plan snapshot
* around until after we start the portal doesn't cost much.
* Start the portal. No parameters here.
*/
PortalStart(portal, NULL, 0, snapshot_set);
/* Done with the snapshot used for parsing/planning */
if (snapshot_set)
PopActiveSnapshot();
PortalStart(portal, NULL, 0, InvalidSnapshot);
/*
* Select the appropriate output format: text unless we are doing a
@ -1733,19 +1727,15 @@ exec_bind_message(StringInfo input_message)
cplan->stmt_list,
cplan);
/*
* And we're ready to start portal execution.
*
* If we took a snapshot for parsing/planning, we'll try to reuse it for
* query execution (currently, reuse will only occur if PORTAL_ONE_SELECT
* mode is chosen).
*/
PortalStart(portal, params, 0, snapshot_set);
/* Done with the snapshot used for parameter I/O and parsing/planning */
if (snapshot_set)
PopActiveSnapshot();
/*
* And we're ready to start portal execution.
*/
PortalStart(portal, params, 0, InvalidSnapshot);
/*
* Apply the result format requests to the portal.
*/