Re: Query run in 27s with 15.2 vs 37ms with 14.6

On Mon, Feb 20, 2023 at 10:56 AM Charles <peacech(at)gmail(dot)com> wrote:

> The plan from 15.2:
>
> Nested Loop (cost=63003.26..64440.14 rows=1 width=89) (actual
> time=23.234..27407.834 rows=779 loops=1)
>

> Plan generated by 14.6
>
> Merge Join (cost=61456.65..61716.09 rows=1 width=89) (actual
> time=25.509..37.185 rows=779 loops=1)
>

Given how close those plan estimates are to each other, I would say your
query was very fragile under 14.6, and it was just a matter of luck of how
the statistics were computed that you got the better plan on the older
version. As opposed to some important coding changes that happened between
versions. To verify that, Can you force each version to choose the other
plan, for example by fiddling with enable_nestedloop on one and
enable_mergjoin on the other?

Cheers,

Jeff