| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Petr Jelinek <petr(at)2ndquadrant(dot)com>, Steve Singer <steve(at)ssinger(dot)info>, Andres Freund <andres(at)2ndquadrant(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Anssi Kääriäinen <anssi(dot)kaariainen(at)thl(dot)fi>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Jaime Casanova <jaime(at)2ndquadrant(dot)com> |
| Subject: | Re: tracking commit timestamps |
| Date: | 2014-11-11 21:56:01 |
| Message-ID: | 20141111215601.GV1791@alvin.alvh.no-ip.org |
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| Lists: | pgsql-hackers pgsql-www |
Jim Nasby wrote:
> On 11/11/14, 2:03 PM, Alvaro Herrera wrote:
> >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.
>
> Well, we're talking about a new feature, so I wasn't looking in back branches. ;P
Well, I did mention <= 9.2 in the text above ...
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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