| From: | "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at> |
|---|---|
| To: | "Alban Hertroys *EXTERN*" <a(dot)hertroys(at)magproductions(dot)nl>, "A(dot) Kretschmer" <andreas(dot)kretschmer(at)schollglas(dot)com> |
| Cc: | <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: more problems with count(*) on large table |
| Date: | 2007-10-01 10:05:18 |
| Message-ID: | D960CB61B694CF459DCFB4B0128514C244378C@exadv11.host.magwien.gv.at |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-general |
Alban Hertroys wrote:
> A. Kretschmer wrote:
>> Again: an index can't help! Because of MVCC: 'select count(*)'
without
>> WHERE-condition forces an seq. table-scan.
>
> That has very little to do with MVCC.
>
> [...] For that it makes no difference whether a seq
> scan or an index scan is performed - both cases need to check at the
> record level whether it's visible (where the seq scan is
> already looking at the actual record, of course).
If you do not use MVCC (say, you use DB2), you need not check
the record itself because if it is there (which it is if there
is an index entry), it will be 'visible'.
> I pleed not guilty ;)
Declined, sorry.
Yours,
Laurenz Albe
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Richard Huxton | 2007-10-01 10:12:20 | Re: ERROR: invalid byte sequence from psql - Works perfectly from pgAdmin III query window |
| Previous Message | Gregory Stark | 2007-10-01 10:04:29 | Re: more problems with count(*) on large table |