| From: | Mark Cave-Ayland <mark(dot)cave-ayland(at)siriusit(dot)co(dot)uk> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Strange issue with GiST index scan taking far too long |
| Date: | 2008-06-09 15:59:26 |
| Message-ID: | 484D535E.5020000@siriusit.co.uk |
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| Lists: | pgsql-hackers |
Tom Lane wrote:
> Is the value you are fetching from the geography table large enough to
> be toasted? I'm thinking you might be looking at the cost of repeated
> de-toastings.
Yeah, it's a fairly large geometry field so it will definitely be
getting toasted. So is it a case of with the mcatest function in place,
we're effectively caching the de-TOASTED value?
> BTW, that mcatest function is buggy --- it's not copying the last
> 4 bytes of the source value. I don't know enough about PostGIS
> data types to know what effect that would have.
It would probably lose that last point in the coordinate sequence, but
nothing major. I've removed the -VARHDRSZ part just to check and it
doesn't make any difference.
Many thanks,
Mark.
--
Mark Cave-Ayland
Sirius Corporation - The Open Source Experts
http://www.siriusit.co.uk
T: +44 870 608 0063
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