From: | Greg Smith <gsmith(at)gregsmith(dot)com> |
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To: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Bgwriter strategies |
Date: | 2007-07-06 10:47:54 |
Message-ID: | Pine.GSO.4.64.0707060638520.3474@westnet.com |
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Lists: | pgsql-hackers |
On Fri, 6 Jul 2007, Heikki Linnakangas wrote:
> There's something wrong with that. The number of buffer allocations shouldn't
> depend on the bgwriter strategy at all.
I was seeing a smaller (closer to 5%) increase in buffer allocations
switching from no background writer to using the stock one before I did
any code tinkering, so it didn't strike me as odd. I believe it's related
to the TPS numbers. When there are more transactions being executed per
unit time, it's more likely the useful blocks will stay in memory because
their usage_count is getting tickled faster, and therefore there's less of
the most useful blocks being swapped out only to be re-allocated again
later.
Since the bad bgwriter tunings reduce TPS, I believe that's the mechanism
by which there are more allocations needed. I'll try to keep an eye on
this now that you've brought it up.
--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD
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