| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Nicholay P(dot) Chuprynin" <kolyan(at)infoport(dot)uz> |
| Cc: | pgsql-admin(at)postgresql(dot)org |
| Subject: | Re: INDEX issues |
| Date: | 2002-04-03 15:55:31 |
| Message-ID: | 9504.1017849331@sss.pgh.pa.us |
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| Lists: | pgsql-admin |
"Nicholay P. Chuprynin" <kolyan(at)infoport(dot)uz> writes:
> I switched enable_seqscan to 'false', restarted server and EXPLAINed the
> same query again:
> ...
> Now it uses index scan, but query takes MUCH more time than before (about
> an hour, and it's not finished yet).
> It seems very strange for me.
Indexscan over a large fraction of a table is not a win compared to
a sequential scan. Random access is just too expensive.
> Can someone explain what's wrong here?
Nothing. The planner knew what it was doing to prefer the seqscan.
regards, tom lane
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