pgsql: Fix corner case in cleanup of transactions using SSI.

Fix corner case in cleanup of transactions using SSI.

When the only remaining active transactions are READ ONLY, we do a "partial
cleanup" of committed transactions because certain types of conflicts
aren't possible anymore. For committed r/w transactions, we release the
SIREAD locks but keep the SERIALIZABLEXACT. However, for committed r/o
transactions, we can go further and release the SERIALIZABLEXACT too. The
problem was with the latter case: we were returning the SERIALIZABLEXACT to
the free list without removing it from the finished list.

The only real change in the patch is the SHMQueueDelete line, but I also
reworked some of the surrounding code to make it obvious that r/o and r/w
transactions are handled differently -- the existing code felt a bit too
clever.

Dan Ports

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/02f377dbe50074a7016f4a476a8d15d294cd0874

Modified Files
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src/backend/storage/lmgr/predicate.c |   26 +++++++++++++++++++++++---
1 files changed, 23 insertions(+), 3 deletions(-)