Re: Synchronized scans

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: Patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Synchronized scans
Date: 2007-06-05 17:48:32
Message-ID: 1181065712.7660.117.camel@dogma.v10.wvs
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On Mon, 2007-06-04 at 10:53 +0100, Heikki Linnakangas wrote:
> I'm now done with this patch and testing it.
>
>

One difference between our patches is that, in my patch, the ending
condition of the scan is after the hint is set back to the starting
position.

That means, in my patch, if you do:
SELECT * FROM bigtable;
SELECT * FROM bigtable;

with no concurrency at all, the returned order will be the same.

In your patch, each full table scan leaves the hint at 16 pages before
the position it started in, leading to different orders on the full
table scans.

Regards,
Jeff Davis

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