Re: Understanding Hash Join performance - Mailing list pgsql-performance

From Claudio Freire
Subject Re: Understanding Hash Join performance
Date
Msg-id BANLkTi=sPMDFd4qyFtPVhtUnsPquWNYC9A@mail.gmail.com
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In response to Re: Understanding Hash Join performance  ("Kevin Grittner" <Kevin.Grittner@wicourts.gov>)
Responses Re: Understanding Hash Join performance  (Robert Haas <robertmhaas@gmail.com>)
List pgsql-performance
On Thu, Jun 2, 2011 at 4:57 PM, Kevin Grittner
<Kevin.Grittner@wicourts.gov> wrote:
> And the
> planner does take the size of work_mem and the expected data set
> into consideration when estimating the cost of the hash join.

And shouldn't it?

In a gross mode, when hash joins go to disk, they perform very poorly.
Maybe the planner should take that into account.

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