| From: | Michael Lewis <mlewis(at)entrata(dot)com> |
|---|---|
| To: | Alexander Stoddard <alexander(dot)stoddard(at)gmail(dot)com> |
| Cc: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Thomas Kellerer <shammat(at)gmx(dot)net>, "pgsql-generallists(dot)postgresql(dot)org" <pgsql-general(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Accounting for between table correlation |
| Date: | 2021-01-15 18:27:26 |
| Message-ID: | CAHOFxGqA_cRbJWXPLOzzrmTE4NwBGy-zWpx-JE0vH4OdJi90RQ@mail.gmail.com |
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| Lists: | pgsql-general |
On Fri, Jan 15, 2021 at 10:22 AM Alexander Stoddard <
alexander(dot)stoddard(at)gmail(dot)com> wrote:
> The 'fast plans' use parallel seq scans. The 'slow plans' is using index
> scans. It appears a good query plan correctly predicts it should be bulk
> processing the tables but bad ones get fooled into trashing (hard disk, not
> SSD) by mispredicting too few rows to join between the tables.
>
How many tables are involved? Are you sure it is stats getting updated
causing the change in behavior? Are you hitting the genetic optimizer?
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