Re: I don't understand that EXPLAIN PLAN timings

Hello David,

Thanks for your answer.

Le 23/01/2024 à 11:41, David Rowley a écrit :
> If you're using psql, if you do \timing on, how long does EXPLAIN take
> without ANALYZE? That also goes through executor startup and shutdown.

You are absolutely correct : the EXPLAIN without ANALYZE gives about the
same results. Also, minimizing the amount of workmem in postgresql.conf
changes drastically the timings. So that means memory allocation is
eating up a lot of time _PER_QUERY_ ?

Since we have quite some RAM on our machines, I dedicated as much as
possible to workmem (initially I was allocating 1GB) but this looks
quite counterproductive (I didn't think that memory was allocated every
time, I thought it was "available" for the current query but not
necessarily used). Is this an issue specific to that version of
PostgreSQL? (I guess no) Or can this be hardware-related? Or OS-related
(both systems on which I have done tests are running Ubuntu, I will try
on Debian)?

Thanks again for your inputs.

Best,

JC