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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: lars <lhofhansl@yahoo.com>
Cc: Ivan Voras <ivoras@freebsd.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: UPDATEDs slowing SELECTs in a fully cached database
Date: Wed, 13 Jul 2011 11:17:41 -0400
Message-ID: <4752.1310570261@sss.pgh.pa.us> (raw)
In-Reply-To: <4E1D697C020000250003F29A@gw.wicourts.gov>
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"Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> ...  Jeff does raise a good point, though -- it seems odd
> that WAL-logging of this pruning would need to be synchronous.

Yeah, we need to get to the bottom of that.  If there's enough
shared_buffer space then it shouldn't be.

> We
> support asynchronous commits -- why not use that feature
> automatically for transactions where the only writes are this sort
> of thing.  Which raises an interesting question -- what happens to
> the timings if your SELECTs are done with synchronous_commit = off?
> I wonder if it would make any sense to implicitly use async commit
> for a transaction which is declared READ ONLY or which never
> acquires and XID?

Huh?  If there was never an XID, there's no commit WAL record, hence
nothing to make asynchronous.

			regards, tom lane



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