"Kevin Grittner" <Kevin.Grittner@xxxxxxxxxxxx> writes: > On Tue, Mar 4, 2008 at 8:42 AM, in message > <483ACAF5-A485-40D9-9D7E-7008EF12F909@xxxxxxxxxxxxxx>, Chris Kratz > <chris.kratz@xxxxxxxxxxxxxx> wrote: >> So, I've now been asked to ping the list as to whether turning off >> nested loops system wide is a bad idea, and why or why not. > In our environment, the fastest plan for a lot of queries involve > nested loops. Of course, it's possible that these never provide the > fasted plan in your environment, but it seems very unlikely -- > you're just not noticing the queries where it's doing fine. Yeah, I seem to recall similar queries from other people who were considering the opposite, ie disabling the other join types :-( The rule of thumb is that nestloop with an inner indexscan will beat anything else for pulling a few rows out of a large table. But on the other hand it loses big for selecting lots of rows. I don't think that a global disable in either direction would be a smart move, unless you run only a very small number of query types and have checked them all. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your Subscription: http://mail.postgresql.org/mj/mj_wwwusr?domain=postgresql.org&extra=pgsql-performance
