Re: Should we cacheline align PGXACT?

Hi,

As discussed at the Developer meeting ~ a week ago, I've ran a number of
benchmarks on the commit, on a small/medium-size x86 machines. I
currently don't have access to a machine as big as used by Alexander
(with 72 physical cores), but it seems useful to verify the patch does
not have negative impact on smaller machines.

In particular I've ran these tests:

* r/o pgbench
* r/w pgbench
* 90% reads, 10% writes
* pgbench with skewed distribution
* pgbench with skewed distribution and skipping

And each of that with a number of clients, depending on the number of
cores available. I've used the usual two boxes I use for all benchmarks,
i.e. a small i5-2500k machine (8GB RAM, 4 cores), and a medium e5-2620v4
box (32GB RAM, 16/32 cores).

Comparing averages of tps, measured on 5 runs (each 5 minutes long), the
difference between master and patched master is usually within 2%, which
is pretty much within noise.

I'm attaching spreadsheets with summary of the results, so that we have
it in the archives. As usual, the scripts and much more detailed results
are available here:

* e5-2620: https://bitbucket.org/tvondra/test-xact-alignment
* i5-2500k: https://bitbucket.org/tvondra/test-xact-alignment-i5

I do plan to run these results on the Power8 box I have access to, but
that will have to wait for a bit, because it's currently doing something
else.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services