Re: postgres 9.3 vs. 9.4

On 19/09/14 08:32, Merlin Moncure wrote:
> On Thu, Sep 18, 2014 at 4:58 AM, Mkrtchyan, Tigran
> <tigran.mkrtchyan@desy.de> wrote:
>>
>> 9.3.5:
>>          0.035940        END;
>>
>>
>> 9.4beta2:
>>          0.957854        END;
>
>
> time being spent on 'END' is definitely suggesting i/o related issues.
> This is making me very skeptical that postgres is the source of the
> problem.   I also thing synchronous_commit is not set properly on the
> new instance (or possibly there is a bug or some such).  Can you
> verify via:
>
> select * from pg_settings where name = 'synchronous_commit';
>
> on both servers?
>

Yes, does look suspicious. It *could* be that the 9.4 case is getting
unlucky and checkpointing just before the end of the 60s run, and 9.3
isn't.

> What is iowait?  For pci-e SSD, these drives don't seem very fast...
>
>
>

These look like rebranded Micron P320's and should be extremely
fast...However I note that my Crucial/Micron M550's are very fast for
most writes *but* are much slower for sync writes (and fsync) that
happen at commit...

Cheers

Mark