Re: Planner misestimation for JOIN with VARCHAR

From: Michael Lewis <mlewis(at)entrata(dot)com>
To: Sebastian Dressler <sebastian(at)swarm64(dot)com>
Cc: "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org>
Subject: Re: Planner misestimation for JOIN with VARCHAR
Date: 2020-06-09 19:30:25
Message-ID: CAHOFxGo4nQ7-KnQ0PrHZLG5ftXc2xY=gK712KRGq6COMKMVMFg@mail.gmail.com
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On Tue, Jun 9, 2020 at 12:34 PM Sebastian Dressler <sebastian(at)swarm64(dot)com>
wrote:

> - Add an index on top of the whole PK
> - Add indexes onto other columns trying to help the JOIN
> - Add additional statistics on two related columns
>
> Another idea I had was to make use of generated columns and hash the PKs
> together to an BIGINT and solely use this for the JOIN. However, this would
> not work when not all columns of the PK are used for the JOIN.
>

Can you expand on the additional statistics you created? Why was it on only
two columns? Did you include MCVs type of extended stats?

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