On Mon, Sep 11, 2017 at 11:47 AM, Tomas Vondra <tomas.von...@2ndquadrant.com> wrote: > The question is what is the optimal replacement_sort_tuples value? I > assume it's the number of tuples that effectively uses CPU caches, at > least that's what our docs say. So I think you're right it to 1B rows > may break this assumption, and make it perform worse. > > But perhaps the fact that we're testing with multiple work_mem values, > and with smaller data sets (100k or 1M rows) makes this a non-issue?
I am not sure that's the case -- I think that before Peter's changes it was pretty easy to find cases where lowering work_mem made sorting ordered data go faster. But I could easily be wrong. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers