FreeBSD 10 and PostgreSQL 9.3 scalability issues

[Palle Girgensohn]

21 maj 2014 kl. 22:05 skrev Sean Chittenden <sean at chittenden.org>:

>>>> I did some tests with zfs, and results where appallingly bad, but that was with db size > ram. 
>>>>> 
>>>>> I think the model used by PostgreSQL, as most databases, are very disk block centric. Using zfs makes it hard to get good performance. But this was some time ago, maybe things have improved.
>>> I have some hardware that I ran with last week wherein I was *not* able to reproduce any performance difference between ZFS and UFS2. On both UFS2 and ZFS I was seeing the same performance when using a a RAID10 / set of mirrors. I talked with the Dragonfly folk who originally performed these tests and they also saw the same thing: no real performance difference between ZFS and UFS. I ran my tests on a host with 16 drive, 10K SAS, 192GB RAM. I also created a kernel profiling image and ran the 20 concurrent user test under kgprof(1), dtrace, and pmcstat and have the results available:
>>> 
>>> http://people.freebsd.org/~seanc/pg9.3-fbsd10-profiling/
>>> 
>>> There are some investigations that are ongoing as a result of these findings. The dfly methodology was observed when generating these results. Stay tuned. -sc
>> 
>> I'm not sure that the ZFS vs UFS2 question is at the core of the
>> performance problem.  We're definitely seeing marked slowdowns between
>> Pg 9.2 and 9.3 on UFS2 (RAID10 + Dell H710p (mfi) raid controller with
>> 1GB NVRAM)


I never meant that it was the core of our problem. Zfs vs ufs is out of scope here. 


> 
> When the working set fits in RAM (OS + PG), there isn't a performance difference between 9.2 and 9.3.
> 
> This is a good data point. I will try and reproduce this workload and will run the performance profiling again to see if something else pops up in the profiling. -sc
> 

I don't agree. My original measurements showed a 20% slowdown for a reasonably small ( <RAM) pgbench database. 

> --
> Sean Chittenden
> sean at chittenden.org
> 
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