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Re: WIP: 2nd-generation buffer ring patch

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: pgsql-patches(at)postgreSQL(dot)org
Subject: Re: WIP: 2nd-generation buffer ring patch
Date: 2007-05-29 22:46:46
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-patches
I wrote:
> Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
>> If there's no easy solution, I think we could live 
>> with that, but Greg's suggestion of bumping the usage_count in PinBuffer 
>> instead of UnpinBuffer sounds like a nice solution to me.

> After thinking about it more, I'm a bit hesitant to do that because it
> will change the interaction with the clock sweep for buffers that stay
> pinned for awhile.  I had suggested making the clock sweep not decrement
> usage_count of a pinned buffer, but I think that would change the
> fairness of the algorithm.  OTOH it may not matter that much if we just
> move the usage_count increment and leave the clock sweep alone.  Do we
> have any decent way of measuring the effectiveness of the clock-sweep
> allocation algorithm?

Despite above misgivings, here's a version of the patch that moves
usage_count incrementing to PinBuffer instead of UnpinBuffer.  It does
seem a good bit cleaner.

			regards, tom lane

Attachment: buffer-ring-3.patch.gz
Description: application/octet-stream (17.7 KB)

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