Hello David,
Thanks for your answer.
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
