Re: Understanding bad estimate (related to FKs?) - Mailing list pgsql-performance

From Michael Lewis
Subject Re: Understanding bad estimate (related to FKs?)
Date
Msg-id CAHOFxGpcN+=Vo10=2roxOOm8UXu8zstdaggRq0vvu00wcC6YjQ@mail.gmail.com
Whole thread Raw
In response to Re: Understanding bad estimate (related to FKs?)  (Philip Semanchuk <philip@americanefficient.com>)
Responses Re: Understanding bad estimate (related to FKs?)  (Philip Semanchuk <philip@americanefficient.com>)
List pgsql-performance
On Mon, Oct 26, 2020 at 11:14 AM Philip Semanchuk <philip@americanefficient.com> wrote:
>> The item I'm focused on is node 23. The estimate is for 7 rows, actual is 896 (multiplied by 1062 loops). I'm confused about two things in this node.
>>
>> The first is Postgres' estimate. The condition for this index scan contains three expressions --
>>
>> (five_uniform = zulu_five.five_uniform) AND
>> (whiskey_mike = juliet_india.whiskey_mike) AND
>> (bravo = 'mike'::text)

Are the columns correlated? Have you tried to create extended statistics and see if the estimate changes? I believe that extended stats will not directly help with joins though, only group bys and perhaps choosing an index scan vs table scan when comparing the correlated columns to static values rather than joining up tables. Wouldn't be much effort to try it though.

pgsql-performance by date:

Previous
From: Philip Semanchuk
Date:
Subject: Re: Understanding bad estimate (related to FKs?)
Next
From: Philip Semanchuk
Date:
Subject: Re: Understanding bad estimate (related to FKs?)