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Re: Load Distributed Checkpoints, take 3

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: Greg Smith <gsmith(at)gregsmith(dot)com>, Patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Load Distributed Checkpoints, take 3
Date: 2007-06-26 17:57:56
Message-ID: 25194.1182880676@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-patches
Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> To recap, the sequence is:

> 1. COPY FROM
> 2. checkpoint
> 3. VACUUM

> Now you have buffer cache full of dirty buffers with usage_count=1,

Well, it won't be very full, because VACUUM works in a limited number of
buffers (and did even before the BufferAccessStrategy patch).

I have no doubt that there are scenarios such as you are thinking about,
but it definitely seems like a corner case that doesn't justify keeping
the all-buffers scan.  That scan is costing us extra I/O in ordinary
non-corner cases, so it's not free to keep it.

			regards, tom lane

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Subject: Re: Load Distributed Checkpoints, take 3
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