On 17/02/15 16:12, Andres Freund wrote:
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.


It's pgbench -j16 -c32


--
 Petr Jelinek                  http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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