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Re: Multixact and prepared transactions

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: hlinnaka(at)iki(dot)fi
Cc: PostgreSQL Bugs <pgsql-bugs(at)postgresql(dot)org>
Subject: Re: Multixact and prepared transactions
Date: 2009-11-23 10:10:09
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-bugs
Heikki Linnakangas wrote:
> Heikki Linnakangas wrote:
>> We seem to have neglected prepared transactions in the logic that tracks
>> the oldest visible multixact. OldestMemberMXactId doesn't contain
>> entries for prepared transactions, so the UPDATE incorrectly considers
>> the multixact as an old obsolete one.
>> A straightforward fix is to enlarge OldestMemberMXactId to make room for
>> max_prepared_transactions extra entries, and at prepare transfer the
>> value of the current backend to one of those slots.
> So here's a patch doing that:


> BTW, I noticed that in deadlock.c, we reserve many working arrays of
> size MaxBackends. But prepared transactions can hold locks too, and
> therefore can be visited by the deadlock checker. Shouldn't we reserve
> space in the arrays for prepared xacts as well? You'll be hard-pressed
> to hit that in practice, given that MaxBackends includes room for
> autovacuum launcher and worker too, and you'd need to have all backends
> involved in the deadlock. But still.

This is still pending.

  Heikki Linnakangas

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