Re: using memoize in in paralel query decreases performance

po 6. 3. 2023 v 9:16 odesílatel David Rowley <dgrowleyml(at)gmail(dot)com> napsal:

> On Mon, 6 Mar 2023 at 20:34, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
> wrote:
> > In one query I can see very big overhead of memoize node - unfortunately
> with hits = 0
> >
> > The Estimate is almost very good. See details in attachment
>
> Are you able to share the version number for this?
>

15.1 - upgrade on 15.2 is planned this month

>
> Also, it would be good to see EXPLAIN ANALYZE *VERBOSE* for the
> memorize plan so we can see the timings for the parallel workers.
>

default https://explain.depesz.com/s/fnBe
disabled memoize https://explain.depesz.com/s/P2rP

> The results of:
>
> EXPLAIN ANALYZE
> SELECT DISTINCT ictc.sub_category_id
> FROM ixfk_ictc_subcategoryid ictc
> INNER JOIN item i ON i.item_category_id = ictc.sub_category_id
> WHERE ictc.super_category_id = ANY
> ('{47124,49426,49488,47040,47128}'::bigint[]);
>
>
https://explain.depesz.com/s/OtCl

would also be useful. That should give an idea of the ndistinct
> estimate. I guess memorize thinks there are fewer unique values than
> the 112 that were found. There's probably not much to be done about
> that. The slowness of the parallel workers seems like a more
> interesting thing to understand.
>
> David
>