On Fri, Jul 14, 2017 at 6:20 PM, Peter Geoghegan <p...@bowt.ie> wrote: > With the additional enhancements made to Postgres 10, I doubt that > there are any remaining cases where it wins.
I tried my favorite sorting test case -- pgbench -i -s 300 and then reindex index pgbench_accounts_pkey. I set maintenance_work_mem to 4MB so that replacement selection would be chosen. On master, this takes ~21.5 seconds; with replacement_sort_tuples = 0, it takes ~19.1 seconds. So, disabling replacement selection is a win. On 9.6, this takes ~19.1 seconds; with replacement_sort_tuples = 0, it takes ~23 seconds. So, disabling replacement selection is a loss. This supports your theory that we should go ahead and remove replacement selection. It does however both me a bit that this test case is apparently slower in master than in 9.6, and not just with very small values of work_mem. With default maintenance_work_mem (64MB), this takes about 13 seconds on 9.6 but about 15 seconds on master -- and with that setting replacement selection is not chosen at all. Any idea what causes this regression? -- 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
