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Re: [HACKERS] WAL logging freezing

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org, pgsql-patches(at)postgresql(dot)org
Subject: Re: [HACKERS] WAL logging freezing
Date: 2006-10-31 16:23:40
Message-ID: 29850.1162311820@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> Simon Riggs wrote:
>> Ouch! We did discuss that also. Flushing the buffercache is nasty with
>> very large caches, so this makes autovacuum much less friendly - and
>> could take a seriously long time if you enforce the vacuum delay
>> costings.

> Hmm, isn't the buffer cache aware of a vacuum operation?

Yeah.  What would probably happen is that we'd dump off most of the
dirtied pages to the kernel, which would likely still have a lot of them
in kernel buffers pending write.  But then we'd have to fsync the table
--- so a physical write storm would ensue, which we have no way to
throttle.

I think the don't-truncate-clog approach is a much better answer.

			regards, tom lane

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