Re: Add min and max execute statement time in pg_stat_statement

On Wed, Jan 29, 2014 at 9:03 AM, KONDO Mitsumasa <
kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp> wrote:

> (2014/01/29 15:51), Tom Lane wrote:
> > KONDO Mitsumasa <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp> writes:
> >> By the way, latest pg_stat_statement might affect performance in
> Windows system.
> >> Because it uses fflush() system call every creating new entry in
> >> pg_stat_statements, and it calls many fread() to warm file cache.
> > This statement doesn't seem to have much to do with the patch as
> > committed. There are no fflush calls, and no notion of warming the
> > file cache either.
> Oh, all right.
>
> > We do assume that the OS is smart enough to keep
> > a frequently-read file in cache ... is Windows too stupid for that?
> I don't know about it. But I think Windows cache feature is stupid.
> It seems to always write/read data to/from disk, nevertheless having large
> memory...
> I'd like to know test result on Windows, if we can...
>
>
I am quite certain the Windows cache is *not* that stupid, and hasn't been
since the Windows 3.1 days.

If you want to make certain, set FILE_ATTRIBUTE_TEMPORARY when the file is
opened, then it will work really hard not to write it to disk - harder than
most Linux fs'es do AFAIK. This should of course only be done if we don't
mind it going away :)

As per port/open.c, pg will set this when O_SHORT_LIVED is specified. But
AFAICT, we don't actually use this *anywhere* in the backend? Perhaps we
should for this - and also for the pgstat files?

(I may have missed a codepath, only had a minute to do some greping)

--
Magnus Hagander
Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/