Re: does max_connections affect the query planner

Thanks Tom.  Will check that.

On Tue, 17 Sep 2019 at 14:13, Tom Lane <[email protected]> wrote:
>
> Bob Jolliffe <[email protected]> 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