From: | Greg Smith <gsmith(at)gregsmith(dot)com> |
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To: | pgsql-patches <pgsql-patches(at)postgresql(dot)org> |
Subject: | Re: bgwriter stats |
Date: | 2007-04-01 07:57:35 |
Message-ID: | Pine.GSO.4.64.0704010329080.27863@westnet.com |
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Lists: | pgsql-patches |
On Thu, 29 Mar 2007, Magnus Hagander wrote:
> I've included a couple of more counters per ideas from Greg Smith in his
> logging patch.
I just submitted a patch that logs the remaining things of value from my
original that couldn't be derived from the information you're collecting.
Between them I'm happy that a lot of previously hidden performance issues
can now be monitored--not necessarily easily, but it's at least possible.
I made one small change to your code in there as well I wanted to
highlight here. You updated the buffers written by checkpoints one at a
time as they wrote out. When I tried to develop something that monitored
pg_stat_bgwriter looking for when checkpoints happened, this made it
difficult to answer the important question "how many buffers did the last
checkpoint write?" just from the stats structure because I assumed it's
possible to get a view in the middle of the checkpoint. It took watching
both the total and the checkpoint count, and that was hard to work with.
I modified things so that the checkpoint buffers written number gets
updated in one shot when the buffer flush is done. No partial results,
much easier to monitor: when the buffers_checkpoint value changes, the
difference from the previous value is what the last checkpoint wrote. I
needed that total anyway which is why I just slipped it into the other
patch.
--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD
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