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Re: [HACKERS] Full page writes improvement

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Koichi Suzuki <suzuki(dot)koichi(at)oss(dot)ntt(dot)co(dot)jp>
Cc: PGSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, pgsql-patches(at)postgresql(dot)org
Subject: Re: [HACKERS] Full page writes improvement
Date: 2007-02-02 01:03:27
Message-ID: 2098.1170378207@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
Koichi Suzuki <suzuki(dot)koichi(at)oss(dot)ntt(dot)co(dot)jp> writes:
> Tom Lane wrote:
>> Doesn't this break crash recovery on PITR slaves?

> Compressed archive log contains the same data as full_page_writes off
> case.   So the influence to PITR slaves is the same as full_page_writes off.

Right.  So what is the use-case for running your primary database with
full_page_writes on and the slaves with it off?  It doesn't seem like
a very sensible combination to me.

Also, it seems to me that some significant performance hit would be
taken by having to grovel through the log files to remove and re-add the
full-page data.  Plus you are actually writing *more* WAL data out of
the primary, not less, because you have to save both the full-page
images and the per-tuple data they normally replace.  Do you have
numbers showing that there's actually any meaningful savings overall?

			regards, tom lane

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