Re: tracking commit timestamps

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Cc: Petr Jelinek <petr(at)2ndquadrant(dot)com>, Steve Singer <steve(at)ssinger(dot)info>, Andres Freund <andres(at)2ndquadrant(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(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: 2014-11-10 13:55:10
Message-ID: CA+Tgmoaxj_QoZijEug861UxN2OiH3kRmwhQhVC_Vk1iKijgzVg@mail.gmail.com
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On Mon, Nov 10, 2014 at 8:40 AM, Alvaro Herrera
<alvherre(at)2ndquadrant(dot)com> 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.

I'm not sure whether keeping it just back to RecentXmin will be enough
for everybody's needs. But we certainly don't need to keep the last
2^32 records as someone-or-other was suggesting.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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