Jim Nasby wrote:
> On 11/10/14, 7:40 AM, Alvaro Herrera wrote:
> >Ah, right. So AFAIK we don't need to keep anything older than
> >RecentXmin or something like that -- which is not too old. If I recall
> >correctly Josh Berkus was saying in a thread about pg_multixact that it
> >used about 128kB or so in <= 9.2 for his customers; that one was also
> >limited to RecentXmin AFAIR. I think a similar volume of commit_ts data
> >would be pretty acceptable. Moreso considering that it's turned off by
> >default.
>
> FWIW, AFAICS MultiXacts are only truncated after a (auto)vacuum process is
> able to advance datminmxid, which will (now) only happen when an entire
> relation has been scanned (which should be infrequent).
>
> I believe the low normal space usage is just an indication that most
> databases don't use many MultiXacts.
That's in 9.3. Prior to that, they were truncated much more often.
Maybe you've not heard enough about this commit:
commit 0ac5ad5134f2769ccbaefec73844f8504c4d6182
Author: Alvaro Herrera <alvhe...@alvh.no-ip.org>
Date: Wed Jan 23 12:04:59 2013 -0300
Improve concurrency of foreign key locking
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Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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