On 09/29/2016 01:59 AM, Robert Haas wrote:
On Wed, Sep 28, 2016 at 6:45 PM, Tomas Vondra
<tomas.von...@2ndquadrant.com> wrote:
So, is 300 too little? I don't think so, because Dilip saw some benefit from
that. Or what scale factor do we think is needed to reproduce the benefit?
My machine has 256GB of ram, so I can easily go up to 15000 and still keep
everything in RAM. But is it worth it?


Dunno. But it might be worth a test or two at, say, 5000, just to
see if that makes any difference.


OK, I have some benchmarks to run on that machine, but I'll do a few tests with scale 5000 - probably sometime next week. I don't think the delay matters very much, as it's clear the patch will end up with RwF in this CF round.

I feel like we must be missing something here.  If Dilip is seeing
huge speedups and you're seeing nothing, something is different, and
we don't know what it is.  Even if the test case is artificial, it
ought to be the same when one of you runs it as when the other runs
it.  Right?


Yes, definitely - we're missing something important, I think. One difference is that Dilip is using longer runs, but I don't think that's a problem (as I demonstrated how stable the results are).

I wonder what CPU model is Dilip using - I know it's x86, but not which generation it is. I'm using E5-4620 v1 Xeon, perhaps Dilip is using a newer model and it makes a difference (although that seems unlikely).

regards

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


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