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Re: synchronized scan: reset state at end of scan

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jeff Davis <pgsql(at)j-davis(dot)com>
Cc: pgsql-patches(at)postgresql(dot)org
Subject: Re: synchronized scan: reset state at end of scan
Date: 2008-06-01 02:01:26
Message-ID: 11636.1212285686@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-patches
Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> I was looking into supporting synchronized scans for VACUUM, and I
> noticed that we currently don't remove the reported scan location as
> this post suggests:

> http://archives.postgresql.org/pgsql-patches/2007-06/msg00047.php

I thought the end conclusion of that thread was to not do anything,
on the grounds that
(1) having new scans sometimes fail to join an existing syncscan
herd would be a bad thing because of the resulting performance
uncertainty;
(2) partially masking the order-nondeterminism created by syncscans
would be a bad thing because it would make it more likely for people
to not notice the issue during testing.

			regards, tom lane

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