| From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Marco Catunda <catunda(at)pobox(dot)com>, Dave Smith <dave(at)candata(dot)com>, pgsql-general(at)postgresql(dot)org |
| Subject: | Re: Doesn't use index, why? |
| Date: | 2001-01-09 06:09:37 |
| Message-ID: | 200101090609.BAA26593@candle.pha.pa.us |
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| Thread: | |
| Lists: | pgsql-general |
> In this case the planner is doing *exactly* the right thing; it is
> smarter than you are. If you want to prove it, force the planner to
> use an indexscan by doing SET ENABLE_SEQSCAN TO OFF. Then time the
> query, and compare the runtime against the seqscan version.
>
> The bottom line here is that a query that needs to touch more than a
> few percent of the rows in a table is better off being done as a
> seqscan.
The only other workaround is to CLUSTER the table on an index, then
force an index scan. That _may_ be faster.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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