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Re: WIP: bufmgr rewrite per recent discussions

From: "Mark Cave-Ayland" <m(dot)cave-ayland(at)webbased(dot)co(dot)uk>
To: "'Tom Lane'" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: <pgsql-patches(at)postgresql(dot)org>
Subject: Re: WIP: bufmgr rewrite per recent discussions
Date: 2005-02-16 17:57:40
Message-ID: 9EB50F1A91413F4FA63019487FCD251D113114@WEBBASEDDC.webbasedltd.local (view raw or flat)
Thread:
Lists: pgsql-patches
> -----Original Message-----
> From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us] 
> Sent: 16 February 2005 17:28
> To: Mark Cave-Ayland
> Cc: pgsql-patches(at)postgresql(dot)org
> Subject: Re: [PATCHES] WIP: bufmgr rewrite per recent discussions

(cut) 

> What do you mean by "pause" exactly?  pgbench doesn't emit 
> any output during a run so I'm not sure what you are watching.

During pgbench I get output on the console similar to the following:

client 1 receiving
client 1 sending end
client 6 receiving
client 6 sending insert into history(tid,bid,aid,delta,mtime)
values(31,6,295341,938,'now')
client 7 receiving
client 7 sending update branches set bbalance = bbalance + 449 where bid = 8
client 6 receiving
client 6 sending end
..etc..

Normally it scrolls faster than I can keep up with, but as described the
test then 'pauses' for a few seconds before continuing at it's normal pace.
It's especially noticeable at 1000 shared buffers, and it occurs
with/without using your patch. I've just actually checked the logfile and
I'm seeing a few messages similar to below:

LOG:  checkpoints are occurring too frequently (7 seconds apart)
HINT:  Consider increasing the configuration parameter
"checkpoint_segments".

I've just tried running again with checkpoint_segments set to 8 but that
doesn't seem to make any difference to the pauses. Perhaps it is something
to do with the drives or filesystem? It's a default FC3 install so it's
using ext3 - this is mirrored across 2 SATA drives with software RAID 1.


Kind regards,

Mark.

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