Hi tom At frist I have thought that the database parsed my explain statement, so the pre-compiled execution plan will be re-used , which made the statement's second run quick.
I think that what you said is right. Thank you 2012/11/7 Tom Lane <t...@sss.pgh.pa.us> > =?UTF-8?B?6auY5YGl?= <luckyjack...@gmail.com> writes: > > It might not be a big problem in a small system. > > But when in a production environment, When I want to use explain and > > then , soon use explain analyze for the same statement, > > How can I avoid the influence of cache and get the right answer for > > evaluating purpose? > > I think this question is based on a false premise. Why do you feel that > the behavior with cold caches is "the right answer", and not the behavior > with warm caches? A short-duration query like this one is not going to > be interesting at all for performance unless it's executed quite a lot, > and if it's executed quite a lot then the warm-cache result ought to be > the more representative one. > > In general, trying to tune for cold-cache cases seems backwards to me. > It's much more productive to try to ensure that the caches are warm. > > regards, tom lane >
