On Apr 26, 2016 4:29 PM, "Peter Devoy" <peter@3xe.co.uk> wrote:
>
> Hi all,
>
> I am trying to work out why a piece of software, Mapnik, is executing
> slowly. All it is doing is loading a config file which causes about
> 12 preparation queries (i.e. with LIMIT 0) to be executed. I can see
> from pg_stat_statements these only take ~1ms in their totality.
>
> So next I ran "perf record -a -g sleep 0.4" and quickly loaded my PHP
> page to start the process (I am interfacing with mapnik via a PHP
> Extension), this is a sample of the result:
>
> https://cloud.githubusercontent.com/assets/4375326/14836015/08b0a8b4-0c05-11e6-96e5-f1836497cdfe.png
I'm no expert in perf, but to me that looks like the profile of a system which is bored. Which matches your description, of spending 0.4 seconds watching something which only takes 0.06 seconds to happen. If you really want to profile this, you should fire it off in a tight loop, using wget or ab2 or curl.
Cheers,
Jeff
