>>>>> "PG" == PG Bug reporting form <noreply@postgresql.org> writes:
PG> After upgrading to v12 from v11.4 I've noticed one of the queries
PG> run by an application has a significant performance degradation.
PG> I've managed to create a toy db that illustrates the issue.
PG> Following is a link of the db and the query in question (there
PG> seems to be no way to attach a file from the web form. If I should
PG> upload them somewhere else let me know)
PG> https://www.dropbox.com/s/6n3ctdn2zohoann/toy-db_and_query.zip?dl=0
You could at least have included the query in the message.
What seems to be happening here looks to me more down to chance than to
any bug. In v11, the join order is constrained by the CTEs, whereas in
v12 it is not; the misplan is the result of a mis-estimated 1-row result
from a subpath that may not have been considered under v11.
--
Andrew (irc:RhodiumToad)