On Fri, May 21, 2010 at 4:53 PM, Richard Yen <d...@richyen.com> wrote: > Any ideas why the query planner chooses a different query plan when using > prepared statements?
A prepared plan is the best one the planner can come up with *in general* for the query in question. If the distribution of the values you're querying against -- in your case, "owner" and "assignment" -- aren't relatively uniform, that plan is going to be suboptimal, if not downright pathological, for the more outlying-ly distributed values. Looking at your prepared plan, it seems that, on average, there are 177 rows for every "assignment", and 184 per "owner". As it turns out, though, nearly a quarter of your table has an "owner" of -1. It's not terribly surprising, with a table that big and a distribution skew of that magnitude, that this query plan, with these arguments, ends up pretty firmly in the "pathological" category. rls -- :wq -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
