| From: | Jim Nasby <jnasby(at)pervasive(dot)com> |
|---|---|
| To: | Brendan Duddridge <brendan(at)clickspace(dot)com> |
| Cc: | chris smith <dmagick(at)gmail(dot)com>, PostgreSQL Performance <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Query using SeqScan instead of IndexScan |
| Date: | 2006-04-04 20:28:24 |
| Message-ID: | B35559FB-1012-4C9A-811B-0F1D37462F34@pervasive.com |
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| Thread: | |
| Lists: | pgsql-performance |
On Apr 1, 2006, at 12:51 PM, Brendan Duddridge wrote:
> from SELECT * FROM pg_stats WHERE tablename='table' AND
> attname='category_id'
>
> I find correlation on category_product for category_id is 0.643703
>
> Would setting the index on category_id to be clustered help with this?
It would absolutely help on the query in question. In my experience,
a correlation of 0.64 is too low to allow an index scan to be used
for anything but a tiny number of rows.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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