On Wed, Jul 29, 2015 at 9:05 PM, Peter Geoghegan <p...@heroku.com> wrote: > The behavior of external sorts that do not require any merge step due > to only having one run (what EXPLAIN ANALYZE output shows as an > "external sort", and not a "merge sort") seems like an area that can > be significantly improved upon. As noted in code comments, this > optimization did not appear in The Art of Computer Programming, Volume > III. It's not an unreasonable idea, but it doesn't work well on modern > machines due to using heapsort, which is known to use the cache > ineffectively. It also often implies significant additional I/O for > little or no benefit. I suspect that all the reports we've heard of > smaller work_mem sizes improving sort performance are actually down to > this one-run optimization *hurting* performance.
Very interesting. And great performance numbers. Thanks for taking the time to investigate this - really cool. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
