| From: | Greg Stark <gsstark(at)mit(dot)edu> |
|---|---|
| To: | Wes <wespvp(at)syntegra(dot)com> |
| Cc: | Greg Stark <gsstark(at)mit(dot)edu>, 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 00:44:44 |
| Message-ID: | 87y8ewx2ir.fsf@stark.xeocode.com |
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| Lists: | pgsql-general pgsql-hackers |
Wes <wespvp(at)syntegra(dot)com> writes:
> On 1/13/05 9:50 AM, "Greg Stark" <gsstark(at)mit(dot)edu> wrote:
>
> Of course, in Oracle 'count(*)' is instantaneous. It doesn't have to count
> the physical records one by one.
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.
--
greg
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