Re: Recommended value for pg_test_fsync

Hi Jeff,

To avoid confusion, Hitachi Storage G900 has 41Gbps Performance bandwidth
(Throughput) and 10Gbps N/W bandwidth.

Thanks and Regards,
Nikhil

On Wed, Jul 1, 2020 at 10:36 PM Nikhil Shetty <nikhil(dot)dba04(at)gmail(dot)com>
wrote:

> Hi Jeff,
>
> Thank you for your inputs. We may stick with fdatasync for now. We will
> get more details on connection details between SAN and server from the
> storage team and update this thread.
>
> Storage is Hitachi G900 with 41Gbps bandwidth.
>
> Thanks and regards,
> Nikhil
>
>
>
> On Tue, Jun 30, 2020 at 9:51 PM Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>
>> On Mon, Jun 29, 2020 at 5:27 AM Nikhil Shetty <nikhil(dot)dba04(at)gmail(dot)com>
>> wrote:
>>
>>> Hi Team,
>>>
>>> We have a PostgreSQL 11.5.6 database running on VM.
>>> RAM - 48GB
>>> CPU - 6 cores
>>> Disk - SSD on SAN
>>>
>>> We wanted to check how the WAL disk is performing using pg_test_fsync.We
>>> ran a test and got around 870 ops/sec for opendatasync and fdatasync and
>>> just 430 ops/sec for fsync.We feel it is quite low as compared to what we
>>> get for local storage(2000 ops/sec for fsync).
>>>
>>
>> It is not surprising to me that SAN would have higher latency than
>> internal storage. What kind of connection do you have between your server
>> and your SAN?
>>
>>
>>> What is the recommended value for fsync ops/sec for PosgreSQL WAL disks
>>> on SAN ?
>>>
>>
>> You have the hardware you have. You can't change it the same way you can
>> change a config file entry, so I don't think that "recommended value"
>> really applies. Is the latency of sync requests a major bottleneck for
>> your workload? pg_test_fsync can tell you what the latency is, but can't
>> tell you how much you care.
>>
>> Cheers,
>>
>> Jeff
>>
>>>