Re: GiST, caching, and consistency

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Matthew Wakeling <matthew(at)flymine(dot)org>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: GiST, caching, and consistency
Date: 2009-08-05 14:11:54
Message-ID: 9731.1249481514@sss.pgh.pa.us
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Matthew Wakeling <matthew(at)flymine(dot)org> writes:
> It is certainly doing a sequential scan. So are you saying that it will
> start a sequential scan from a different part of the table each time, even
> in the absence of other simultaneous sequential scans?

Yeah, that's the syncscan logic biting you. You can turn it off if you
want.

> Some trivial testing with "select * from location limit 10;" indicates
> that it starts the sequential scan in the same place each time - but is
> this different from the above query?

Yup, you're not scanning enough of the table to move the syncscan start
pointer.

regards, tom lane

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