Re: Move PinBuffer and UnpinBuffer to atomics

On Thu, Apr 14, 2016 at 8:05 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> On 2016-04-14 07:59:07 +0530, Amit Kapila wrote:
> > What you want to see by prewarming?
>
> Prewarming appears to greatly reduce the per-run variance on that
> machine, making it a lot easier to get meaningful results.
>

I think you are referring the tests done by Robert on power-8 m/c, but the
performance results I have reported were on intel x86. In last two days, I
have spent quite some effort to do the performance testing of this patch
with pre-warming by using the same query [1] as used by Robert in his
tests. The tests are done such that first it start server, pre-warms the
relations, ran read-only test, stop server, again repeat this for next
test. I have observed that the variance in run-to-run performance still
occurs especially at higher client count (128). Below are results for 128
client count both when the tests ran first with patch and then with HEAD
and vice versa.

Test-1
----------
client count - 128 (basically -c 128 -j 128)

first tests ran with patch and then with HEAD

Patch_ver/Runs HEAD (commit -70715e6a) Patch
Run-1 156748 174640
Run-2 151352 150115
Run-3 177940 165269

Test-2
----------
client count - 128 (basically -c 128 -j 128)

first tests ran with HEAD and then with patch

Patch_ver/Runs HEAD (commit -70715e6a) Patch
Run-1 173063 151282
Run-2 173187 140676
Run-3 177046 166726

I think this patch (padding pgxact) certainly is beneficial as reported
above thread. At very high client count some variation in performance is
observed with and without patch, but I feel in general it is a win.

[1] - psql -c "select sum(x.x) from (select pg_prewarm(oid) as x from
pg_class where relkind in ('i', 'r') order by oid) x;"

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com