Re: Speed up Clog Access by increasing CLOG buffers

On Sun, Feb 21, 2016 at 7:45 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
wrote:

> I mean, my basic feeling is that I would not accept a 2-3% regression in
>> the single client case to get a 10% speedup in the case where we have 128
>> clients.
>>
>
> I understand your point. I think to verify whether it is run-to-run
> variation or an actual regression, I will re-run these tests on single
> client multiple times and post the result.
>

Perhaps you could also try it on a couple of different machines (e.g.
MacBook Pro and a couple of different large servers).

>
> A lot of people will not have 128 clients; quite a few will have a
>> single session, or just a few. Sometimes just making the code more complex
>> can hurt performance in subtle ways, e.g. by making it fit into the L1
>> instruction cache less well. If the numbers you have here are accurate,
>> I'd vote to reject the patch.
>>
> One point to note is that this patch along with first patch which I
> posted in this thread to increase clog buffers can make significant
> reduction in contention on CLogControlLock. OTOH, I think introducing
> regression at single-client is also not a sane thing to do, so lets
> first try to find if there is actually any regression and if it is, can
> we mitigate it by writing code with somewhat fewer instructions or
> in a slightly different way and then we can decide whether it is good
> to reject the patch or not. Does that sound reasonable to you?
>

Yes.

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Robert Haas
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