| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | mlw <markw(at)mohawksoft(dot)com> |
| Cc: | Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, Louis-David Mitterrand <vindex(at)apartia(dot)org>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Index Scans become Seq Scans after VACUUM ANALYSE |
| Date: | 2002-04-17 13:55:33 |
| Message-ID: | 5747.1019051733@sss.pgh.pa.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
mlw <markw(at)mohawksoft(dot)com> writes:
> If the DBA notices that there is a problem with a query, he adds an
> index, he notices that there is no difference, then he notices that
> PostgreSQL is not using his index. First and foremost he gets mad at
> PostgreSQL for not using his index. If PostgreSQL decided to use an
> index which increases execution time, the DBA would delete the
> index.
I don't buy that argument at all. It might be a unique index that he
must have in place for data integrity reasons. It might be an index
that he needs for a *different* query.
If the table has more than one index available that might be usable
with a particular query, how does your argument help? It doesn't.
We still have to trust to statistics and cost estimates. So I intend
to proceed on the path of improving the estimator, not in the direction
of throwing it out in favor of rules-of-thumb.
regards, tom lane
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Michael Loftis | 2002-04-17 14:08:27 | Re: Index Scans become Seq Scans after VACUUM ANALYSE |
| Previous Message | Louis-David Mitterrand | 2002-04-17 13:52:07 | huge runtime difference between 2 almost identical queries (was: Re: Index Scans become Seq Scans after VACUUM ANALYSE) |