Robert Haas wrote:
> On Sun, Nov 9, 2014 at 8:41 PM, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> > Robert Haas wrote:
> >> I think the key question here is the time for which the data needs to
> >> be retained. 2^32 of anything is a lot, but why keep around that
> >> number of records rather than more (after all, we have epochs to
> >> distinguish one use of a given txid from another) or fewer?
> >
> > The problem is not how much data we retain; is about how much data we
> > can address.
>
> I thought I was responding to a concern about disk space utilization.
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.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
