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Re: Do checkpoints flush all data from shared buffers ?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Fabrice Franquenk <Fabrice(dot)Franquenk(at)bull(dot)net>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: Do checkpoints flush all data from shared buffers ?
Date: 2006-07-13 22:36:31
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Lists: pgsql-novice
Fabrice Franquenk <Fabrice(dot)Franquenk(at)bull(dot)net> writes:
> Because i was trying to lower I/Os of the disks, i got the checkpoint 
> timeout lowered to 150 seconds so i get twice the number the checkpoint. 
> I was hoping it would reduce the number of  I/Os on the disks because 
> there would be less data to write in datafiles...

No, that's going to *increase* the amount of I/O: pages will be forced
to disk more often, and what's worse you'll be increasing the volume of
WAL data because of extra post-checkpoint page images written to WAL.

As a rule of thumb, you want checkpoints to occur as far apart as you
can stand, remembering that a longer distance back to the last
checkpoint means longer recovery time after a crash.

			regards, tom lane

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