From: | Csaba Nagy <nagy(at)ecircle-ag(dot)com> |
---|---|
To: | "John D(dot) Burger" <john(at)mitre(dot)org> |
Cc: | Postgres general mailing list <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: The planner chooses seqscan+sort when there is an |
Date: | 2006-05-03 16:42:00 |
Message-ID: | 1146674520.14093.185.camel@coppola.muc.ecircle.de |
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Lists: | pgsql-general |
> Docs say:
>
> > Enables or disables the query planner's use of sequential scan plan
> > types. It's not possible to suppress sequential scans entirely, but
> > turning this variable off discourages the planner from using one if
> > there are other methods available.
>
> Note the second sentence. Again, I think it will have to scan the
> whole table anyway, because that's what you've asked for, and given
> that, enable_seqscan=off doesn't apply.
OK, maybe that's the point... the "cost bust" given to the sequential
scan by enable_seqscan=off is not enough in this case to exceed the cost
of the index scan ? The table is quite big, might be possible. I still
wonder why would be seqscan+sort faster than index scan... the sort will
for sure have to write to disk too given the size of the table...
Cheers,
Csaba.
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