Re: Planner performance in partitions

"It is also important to consider the overhead of partitioning during query
planning and execution. The query planner is generally able to handle
partition hierarchies with *up to a few hundred partitions fairly well*,
provided that typical queries allow the query planner to prune all but a
small number of partitions. Planning times become longer and memory
consumption becomes higher as more partitions are added." (emphasis added)

--https://www.postgresql.org/docs/current/ddl-partitioning.html