Bob Jolliffe <bobjolliffe@gmail.com> writes:
> We do know that max_connections is set quite high (600) when we don't
> really expect more than 100. I wonder does the planner take
> max_connections x work_mem into account when considering the memory it
> has potentially available?
No. There have been discussions to the effect that it ought to have
a more holistic view about available memory; but nothing's been done
about that, and certainly no existing release does so.
Usually the proximate cause of bad plan choices is bad rowcount
estimates --- you can spot that by comparing estimated and actual
rowcounts in EXPLAIN ANALYZE results.
regards, tom lane