PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> In my humble opinion, this query should not be blocked during planning, as
> the partition can be pruned directly from the plan with the partition
> information that is available from the parent table: Partition information
> can be updated when the partition is locked, but through the parent
> partitioned table.
This case has been improved in PG v12. It is operating as designed in
v11, however.
regards, tom lane