Should we warn against using too many partitions?

Over on [1] I raised a concern about the lack of any warning in our
documents to inform users that they might not want to use thousands of
partitions.  More recently there's [2], also suffering from OOM using
100 partitions.  Perhaps there's more too this, but the planner using
a lot of memory planning updates and deletes to partitioned tables
does seem to be a surprise to many people.

I had hoped we could get something it the documents sooner rather than
later about this. Probably the v12 patch will need to be adjusted now
that the memory consumption will be reduced when many partitions are
pruned, but I still think v12 needs to have some sort of warning in
there.

https://commitfest.postgresql.org/23/2065/

I'm moving this to a new thread with a better title, rather than
tagging onto that old thread that's become rather long.

[1] https://www.postgresql.org/message-id/CAKJS1f8RW-mHQ8aEWD5Dv0+8A1wH5tHHdYMGW9y5sXqnE0X9wA@mail.gmail.com
[2] https://www.postgresql.org/message-id/87ftp6l2qr.fsf@credativ.de

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services