Re: Recommended value for pg_test_fsync

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

>