Eric Schwarzenbach wrote: > This is in a sense a followup to my post with subject "Wildly erratic > query performance". The more I think about it the only thing that makes > sense of my results is if the query planner really WAS choosing my join > order truly randomly each time. I went digging into the manual and > Section 49.3.1. "Generating Possible Plans with GEQO" says > > "In the initial stage, the GEQO code simply generates some possible join > sequences at random." > > Now ordinarily I would interpret this use of the word random loosely, to > mean "arbitrarily" or using some non-meaningful selection criteria. But > given what I am seeing, this leads me to consider that "random" is meant > literally, and that it uses a random number generate to pick paths. Can > someone confirm that this is the case? Yes, "random" means random. > Is this really a good idea? Is non-deterministic behavior really > acceptable? I would think it would be much more sensible to have it > operate deterministically (such as with some predetermined random > sequence of numbers used repeatedly). Uh, no one has ever asked for that. -- Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us EnterpriseDB http://enterprisedb.com + If your life is a hard drive, Christ can be your backup. + -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
