Re: Speed up Clog Access by increasing CLOG buffers

On Wed, Sep 28, 2016 at 9:10 PM, Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>> 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).

It's not impossible that the longer runs could matter - performance
isn't necessarily stable across time during a pgbench test, and the
longer the run the more CLOG pages it will fill.

> 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).

The fact that he's using an 8-socket machine seems more likely to
matter than the CPU generation, which isn't much different. Maybe
Dilip should try this on a 2-socket machine and see if he sees the
same kinds of results.

--
Robert Haas
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