Re: Choice of bitmap scan over index scan - Mailing list pgsql-performance

From Robert Haas
Subject Re: Choice of bitmap scan over index scan
Date
Msg-id 603c8f071001101852n7ce69d9atfc0b7aa65d8e357d@mail.gmail.com
Whole thread Raw
In response to Re: Choice of bitmap scan over index scan  ("Kevin Grittner" <Kevin.Grittner@wicourts.gov>)
Responses Re: Choice of bitmap scan over index scan  (Mathieu De Zutter <mathieu@dezutter.org>)
List pgsql-performance
On Sun, Jan 10, 2010 at 10:53 AM, Kevin Grittner
<Kevin.Grittner@wicourts.gov> wrote:
> seq_page_cost = 0.1
> random_page_cost = 0.1

These might not even be low enough.  The reason why bitmap index scans
win over plain index scans, in general, is because you make one pass
through the heap to get all the rows you need instead of bouncing
around doing lots of random access.  But of course if all the data is
in RAM then this argument falls down.

If these aren't enough to get the query planner to DTRT, then the OP
might want to try lowering them further and seeing how low he has to
go to flip the plan...

...Robert

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