| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Lincoln Yeoh <lyeoh(at)pop(dot)jaring(dot)my> |
| Cc: | mlw <markw(at)mohawksoft(dot)com>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, Andrew Sullivan <andrew(at)libertyrms(dot)info>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Index Scans become Seq Scans after VACUUM ANALYSE |
| Date: | 2002-04-20 04:16:15 |
| Message-ID: | 18463.1019276175@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Lincoln Yeoh <lyeoh(at)pop(dot)jaring(dot)my> writes:
> ...By the way, are updates treated the same as selects by the optimizer?
Yeah. The writes must occur in any case, so I see no reason why the
optimizer should worry about them. All it needs to consider are the
cycles used by the various alternatives for fetching the data. So
the problem is isomorphic to a SELECT.
This assumption is really wired quite fundamentally into the optimizer,
but I'm not sure if it's made clear anywhere in the documentation.
Can anyone suggest the right place to describe it?
regards, tom lane
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