From: | Chris Browne <cbbrowne(at)acm(dot)org> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Alternative for vacuuming queue-like tables |
Date: | 2006-04-28 15:55:27 |
Message-ID: | 60fyjxd79s.fsf@dba2.int.libertyrms.com |
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Thread: | |
Lists: | pgsql-general |
nagy(at)ecircle-ag(dot)com (Csaba Nagy) writes:
> On Fri, 2006-04-28 at 15:20, kmh496 wrote:
>> 2006-04-28 (ê¸), 14:40 +0200, Csaba Nagy ì°ì길:
>> > I placed a cron job to
>> > cluster the queue table on it's PK index.
>> what does that mean?
>
> Means execute:
>
> CLUSTER pk_queue_table ON queue_table;
>
> See http://www.postgresql.org/docs/8.1/static/sql-cluster.html for more
> details on CLUSTER.
>
> This will actually rebuild the table I guess after it can lock it
> exclusively. Due to the fact that the queue transactions are very short
> lived, the exclusive lock is fast acquired and the clustering operation
> is also fast as the table has only a few entries.
>
> I'm not sure how this operation can work in the presence of other long
> running transactions which did not touch the queue table yet, but it
> actually does work, I can confirm that. Is it violating MVCC maybe ?
There is, I believe, a problem there; there is a scenario where data
can get "dropped out from under" those old connections.
This has been added to the TODO...
http://www.postgresql.org/docs/faqs.TODO.html
* Make CLUSTER preserve recently-dead tuples per MVCC requirements
--
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