Re: tracking commit timestamps

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/
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