Re: PostgreSQL performance on FreeBSD

> 28 jun 2014 kl. 12:21 skrev Konstantin Belousov <kostikbel_at_gmail.com>:
> 
>> On Sat, Jun 28, 2014 at 12:08:39PM +0200, Palle Girgensohn wrote:
>> 
>> 
>>> 27 jun 2014 kl. 18:34 skrev Konstantin Belousov <kostikbel_at_gmail.com>:
>>> 
>>>> On Fri, Jun 27, 2014 at 10:57:53AM -0400, John Baldwin wrote:
>>>>> On Friday, June 27, 2014 8:56:13 am Konstantin Belousov wrote:
>>>>> Hi,
>>>>> I did some measurements and hacks to see about the performance and
>>>>> scalability of PostgreSQL 9.3 on FreeBSD, sponsored by The FreeBSD
>>>>> Foundation.
>>>>> 
>>>>> The results are described in https://kib.kiev.ua/kib/pgsql_perf.pdf.
>>>>> The uncommitted patches, referenced in the article, are available as
>>>>> https://kib.kiev.ua/kib/pig1.patch.txt
>>>>> https://kib.kiev.ua/kib/patch-2
>>>> 
>>>> Did you run the same benchmark on the same hardware with any other OS's to 
>>>> compare results?
>>> 
>>> No.
>>> 
>>> FWIW, before the failing after the 30 clients is corrected, I do not
>>> think it is much interesting to do such comparision.
>> 
>> This is great work!
>> 
>> Does anybody know how far back in FreeBSD versions using posix semaphore instead of sysv would make a difference?  It seems we need a rather current version? 8.x did not support it at all, at some point at lest, and in 9 it was buggy. I could add he patch-2 to the port, but I reckon it needs a conditional based on FreeBSD version?
> I recommend to add it as an option.  The currently supported versions
> of stable/9 and higher have new posix semaphores implementation.
> The stable/8 also has posix semaphores, but there it is kernel-based
> interface, I do not plan to evaluate it in any way.

According to one source, posix semaphores uses O(N^2) file descriptors, where N is the number of connections. Do you know if this is true? (I'll try it, naturally, just checking). 

> 
> 
>> The clang bug should go upstreams, right?
> I believe there is already some activity about it.  I do not follow
> clang development.

Sounds good enough. 

> 
>> 
>> I have seen similar curves, presented by Greg Smith (PostgreSQL
>> hacker) where he concluded that there is no point in running more
>> than 50 concurrent connections. This was for Linux. In your measures,
>> the knee is at 30. That's said, FreeBSD could and should do better,
>> but probably there is a limit where there will be a knee in the graph
>> and performance will drop. It should be more than 30, though, as you
>> rightly commented.
>> 
>> Do you any ideas to pursue this further apart from complicated
>> rewrites like DragonFly?
> I do.
> 
> The scope of the current work was done to obtain understanding where do we stay
> and, if possible, evaluate ideas, possibly in the hackish way. I hope
> and almost sure that this will be continued, but cannot provide any time
> estimation.

Great. If you need help testing, I might be able to help. 

Cheers,
Palle