Re: pg_test_fsync performance

On Mon, Feb 13, 2012 at 08:28:03PM -0500, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
> > Instead of or in addition to a fixed number operations per test, maybe
> > we should cut off each test after a certain amount of wall-clock time,
> > like 15 seconds.
>
> +1, I was about to suggest the same thing.  Running any of these tests
> for a fixed number of iterations will result in drastic degradation of
> accuracy as soon as the machine's behavior changes noticeably from what
> you were expecting.  Run them for a fixed time period instead.  Or maybe
> do a few, then check elapsed time and estimate a number of iterations to
> use, if you're worried about the cost of doing gettimeofday after each
> write.

Good idea, and it worked out very well.  I changed the -o loops
parameter to -s seconds which calls alarm() after (default) 2 seconds,
and then once the operation completes, computes a duration per
operation.

The test now runs in 30 seconds and produces similar output to the
longer version.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +