Indeed an index cannot really be used for sorting here, based on the complexity of the returned fields.
Wich strikes me is that if I try to simplify it a lot, removing all data but the main table (occtax.observation) primary key cd_nom and aggregate, the query plan should be able tu use the cd_nom index for sorting and provide better query plan (hash aggregate), but it does not seems so :
It is better, but I think 10s for such a query seems bad perf for me.
Regards
Michaël
Le ven. 22 févr. 2019 à 19:06, Tom Lane <tgl@sss.pgh.pa.us> a écrit :
Michael Lewis <mlewis@entrata.com> writes: > Does the plan change significantly with this- > set session work_mem='250MB'; > set session geqo_threshold = 20; > set session join_collapse_limit = 20;
Yeah ... by my count there are 16 tables in this query, so raising join_collapse_limit to 15 is not enough to ensure that the planner considers all join orders. Whether use of GEQO is a big problem is harder to say, but it might be.
