From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Gurjeet Singh <gurjeet(at)singh(dot)im>, PGSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Proposing pg_hibernate |
Date: | 2014-06-04 13:56:57 |
Message-ID: | 20140604135657.GA10482@alap3.anarazel.de |
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Thread: | |
Lists: | pgsql-hackers |
On 2014-06-04 09:51:36 -0400, Robert Haas wrote:
> On Wed, Jun 4, 2014 at 2:08 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> > On 2014-06-04 10:24:13 +0530, Amit Kapila wrote:
> >> Incase of recovery, the shared buffers saved by this utility are
> >> from previous shutdown which doesn't seem to be of more use
> >> than buffers loaded by recovery.
> >
> > Why? The server might have been queried if it's a hot standby one?
>
> I think that's essentially the same point Amit is making. Gurjeet is
> arguing for reloading the buffers from the previous shutdown at end of
> recovery; IIUC, Amit, you, and I all think this isn't a good idea.
I think I am actually arguing for Gurjeet's position. If the server is
actively being queried (i.e. hot_standby=on and actually used for
queries) it's quite reasonable to expect that shared_buffers has lots of
content that is *not* determined by WAL replay.
There's not that much read IO going on during WAL replay anyway - after
a crash/start from a restartpoint most of it is loaded via full page
anyway. So it's only disadvantageous to fault in pages via pg_hibernate
if that causes pages that already have been read in via FPIs to be
thrown out.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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