Re: How to evaluate "explain analyze" correctly soon after "explain" for the same statement ?

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 <tgl(at)sss(dot)pgh(dot)pa(dot)us>

> =?UTF-8?B?6auY5YGl?= <luckyjackgao(at)gmail(dot)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
>