Re: stats for network traffic WIP

On Tue, Dec 10, 2013 at 10:59 AM, Fujii Masao <masao.fujii@gmail.com> wrote:
> On Tue, Dec 10, 2013 at 6:56 AM, Nigel Heron <nheron@querymetrics.com> wrote:
>> On Sat, Dec 7, 2013 at 1:17 PM, Fujii Masao <masao.fujii@gmail.com> wrote:
>>>
>>> Could you share the performance numbers? I'm really concerned about
>>> the performance overhead caused by this patch.
>>>
>>
>> I've tried pgbench in select mode with small data sets to avoid disk
>> io and didn't see any difference. That was on my old core2duo laptop
>> though .. I'll have to retry it on some server class multi core
>> hardware.
>
> When I ran pgbench -i -s 100 in four parallel, I saw the performance difference
> between the master and the patched one. I ran the following commands.
>
>     psql -c "checkpoint"
>     for i in $(seq 1 4); do time pgbench -i -s100 -q db$i & done
>
> The results are:
>
> * Master
>   10000000 of 10000000 tuples (100%) done (elapsed 13.91 s, remaining 0.00 s).
>   10000000 of 10000000 tuples (100%) done (elapsed 14.03 s, remaining 0.00 s).
>   10000000 of 10000000 tuples (100%) done (elapsed 14.01 s, remaining 0.00 s).
>   10000000 of 10000000 tuples (100%) done (elapsed 14.13 s, remaining 0.00 s).
>
>   It took almost 14.0 seconds to store 10000000 tuples.
>
> * Patched
>   10000000 of 10000000 tuples (100%) done (elapsed 14.90 s, remaining 0.00 s).
>   10000000 of 10000000 tuples (100%) done (elapsed 15.05 s, remaining 0.00 s).
>   10000000 of 10000000 tuples (100%) done (elapsed 15.42 s, remaining 0.00 s).
>   10000000 of 10000000 tuples (100%) done (elapsed 15.70 s, remaining 0.00 s).
>
>   It took almost 15.0 seconds to store 10000000 tuples.
>--
Regards,

Atri
l'apprenant
> Thus, I'm afraid that enabling network statistics would cause serious
> performance
> degradation. Thought?

Hmm, I think I did not push it this high. The performance numbers here
are cause of worry.

Another point I may mention here is that if we can isolate a few
points of performance degradation and work on them because I still
feel that the entire patch itself does not cause a serious lapse,
rather, a few points may.

However, the above numbers bring up the original concerns for the
performance voiced. I guess I was testing on too low number of clients
for the gap to show up significantly.

Regards,

Atri