| From: | Neil Conway <neilc(at)samurai(dot)com> |
|---|---|
| To: | <simon(at)2ndquadrant(dot)com> |
| Cc: | "'Mark Kirkwood'" <markir(at)paradise(dot)net(dot)nz>, "'Randolf Richardson'" <rr(at)8x(dot)ca>, <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: *sigh* |
| Date: | 2004-01-04 16:23:22 |
| Message-ID: | m2ekuflm2t.fsf@mailbox.samurai.com |
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| Lists: | pgsql-hackers |
"Simon Riggs" <simon(at)2ndquadrant(dot)com> writes:
> Select count(*) could be evaluated against any available index
> sub-tables, since all that is required is to count the rows. That would
> be significantly faster than a full file scan and accurate too.
PostgreSQL stores MVCC information in heap tuples only, so index-only
plans such as you're suggesting can't be used (i.e. we need to check
the heap tuple to see if a particular index entry is visible to the
current transaction).
-Neil
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