On 2015-02-17 15:50:39 +0100, Petr Jelinek wrote:
> On 17/02/15 03:07, Petr Jelinek wrote:
> >On 17/02/15 03:03, Andrew Dunstan wrote:
> >>On 02/16/2015 08:57 PM, Andrew Dunstan wrote:
> >>>>Average of 3 runs of read-only pgbench on my system all with
> >>>>pg_stat_statement activated:
> >>>>HEAD: 20631
> >>>>SQRT: 20533
> >>>>SQRTD: 20592
> >>>So using sqrtd the cost is 0.18%. I think that's acceptable.
> >>Actually, sqrt/sqrtd is not called in accumulating the stats, only in
> >>the reporting function. So it looks like the difference here should be
> >>noise. Maybe we need some longer runs.
> >Yes there are variations between individual runs so it might be really
> >just that, I can leave it running for much longer time tomorrow.
> Ok so I let it run for more than hour on a different system, the difference
> is negligible - 14461 vs 14448 TPS. I think there is bigger difference
> between individual runs than between the two versions...
These numbers sound like you measured them without concurrency, am I
right? If so, the benchmark isn't that interesting - the computation
happens while a spinlock is held, and that'll mainly matter if there are
many backends running at the same time.
Greetings,
Andres Freund
-- Andres Freund http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services