| From: | Wes <wespvp(at)syntegra(dot)com> |
|---|---|
| To: | Greg Stark <gsstark(at)mit(dot)edu> |
| Cc: | Csaba Nagy <nagy(at)ecircle-ag(dot)com>, Postgres general mailing list <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] Much Ado About COUNT(*) |
| Date: | 2005-01-14 17:04:43 |
| Message-ID: | BE0D57CB.3FAF%wespvp@syntegra.com |
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| Lists: | pgsql-general pgsql-hackers |
On 1/13/05 6:44 PM, "Greg Stark" <gsstark(at)mit(dot)edu> wrote:
> That's simply false. Oracle does indeed have to count the records one by one.
>
> It doesn't have to read and ignore the dead records since they're in a
> separate place (but on the other hand it sometimes have to go read that
> separate place when it sees records that were committed after your
> transaction).
>
> It can also do index-only scans, which often helps, but it's still not
> instantaneous.
Ok, I stand corrected - I was given some wrong information. However, my
experience has been that count(*) on Oracle is a whole lot faster than
PostgreSQL - what appeared instantaneous on Oracle took some time on
PostgreSQL. That was one of the first things I noticed when moving a
database application to PostgreSQL. I've since disposed of the Oracle
database, so can't go back and retest.
Wes
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