| From: | Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au> |
|---|---|
| To: | Dann Corbit <DCorbit(at)connx(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Peter Bierman <bierman(at)apple(dot)com>, <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Suggestion for optimization |
| Date: | 2002-04-06 10:43:27 |
| Message-ID: | 20020406184224.B99366-100000@houston.familyhealth.com.au |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
> AFAICS, making them exact would not improve the planning estimates
> at all, because there are too many other sources of error. We have
> approximate stats already via vacuum/analyze statistics gathering.
> >>
> What happens if someone deletes 75% of a table?
> What happens if someone imports 30 times more rows than are already in
> the table?
> What happens if one table is remarkably small or even empty and you are
> unaware?
If you are unaware of any of the above, you'll get poorer performance.
Just make sure you run ANALYZE often enough. Anyone who does a massive
change in the number of rows in a table, or updates most of a table should
always do an ANALYZE afterwards.
Chris
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