| From: | Tomasz Myrta <jasiek(at)klaster(dot)net> |
|---|---|
| To: | Dror Matalon <dror(at)zapatec(dot)com> |
| Cc: | "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: count(*) slow on large tables |
| Date: | 2003-10-02 19:36:42 |
| Message-ID: | 3F7C7E4A.9080803@klaster.net |
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| Thread: | |
| Lists: | pgsql-hackers pgsql-performance |
> Hi,
>
> I have a somewhat large table, 3 million rows, 1 Gig on disk, and growing. Doing a
> count(*) takes around 40 seconds.
>
> Looks like the count(*) fetches the table from disk and goes through it.
> Made me wonder, why the optimizer doesn't just choose the smallest index
> which in my case is around 60 Megs and goes through it, which it could
> do in a fraction of the time.
>
> Dror
Just like other aggregate functions, count(*) won't use indexes when
counting whole table.
Regards,
Tomasz Myrta
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