Note: PostgreSQL 18 includes many optimisations related to partitions; because of this, the improvement may be smaller. ( https://www.postgresql.org/docs/18/release-18.html )

  -- "Improve the efficiency of planning queries accessing many partitions (Ashutosh Bapat, Yuya Watari, David Rowley)"

  ..."The actual performance increases here are highly dependent on the number
  of partitions and the query being planned.  Performance increases can be
  visible with as few as 8 partitions, but the speedup is marginal for
  such low numbers of partitions.  The speedups become much more visible
  with a few dozen to hundreds of partitions.  With some tested queries
  using 56 partitions, the planner was around 3x faster than before.  For
  use cases with thousands of partitions, these are likely to become
  significantly faster.  Some testing has shown planner speedups of 60x or
  more with 8192 partitions."
  https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=d69d45a5a