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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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18
src/backend/executor/spi.c
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@ -1126,6 +1126,7 @@ SPI_cursor_open_internal(const char *name, SPIPlanPtr plan,
CachedPlan *cplan;
List *stmt_list;
char *query_string;
Snapshot snapshot;
MemoryContext oldcontext;
Portal portal;
@ -1268,6 +1269,15 @@ SPI_cursor_open_internal(const char *name, SPIPlanPtr plan,
}
}
/* Set up the snapshot to use. */
if (read_only)
snapshot = GetActiveSnapshot();
else
{
CommandCounterIncrement();
snapshot = GetTransactionSnapshot();
}
/*
* If the plan has parameters, copy them into the portal. Note that this
* must be done after revalidating the plan, because in dynamic parameter
@ -1283,13 +1293,7 @@ SPI_cursor_open_internal(const char *name, SPIPlanPtr plan,
/*
* Start portal execution.
*/
if (read_only)
PortalStart(portal, paramLI, 0, true);
else
{
CommandCounterIncrement();
PortalStart(portal, paramLI, 0, false);
}
PortalStart(portal, paramLI, 0, snapshot);
Assert(portal->strategy != PORTAL_MULTI_QUERY);