Re: WALWriteLocks

On Mon, May 24, 2021 at 10:38 AM Vijaykumar Jain <
vijaykumarjain(dot)github(at)gmail(dot)com> wrote:

> Thanks.
>
> For my ref:
> Virtual machine and disk performance - Azure Virtual Machines | Microsoft
> Docs
> <https://docs.microsoft.com/en-us/azure/virtual-machines/disks-performance>
>

We've definitely been over these docs, with and without their support team.
We are well below the caps on the both the disks and the VM size in use.

> Sorry, i just want to use all the info, i have less exp :)
> do you generate large wals ?
>

Our WALs are standard 16MB in size.

> if your checkpoint_completion_target is aggressive, it will result in a
> lot of io.
> if the checkpoint is spread over a larger time window, maybe it will
> reduce frequent i/o pressure.
> but for that log_checkpoints needs to be turned on if they are hogging the
> iops.
>

checkpoint_timeout is 5min, max_wal_size is 5GB. The vast majority of
checkpoints are time-initiated, not wal-initiated. We've tuned this in the
past. Over the past 16 hours there have been only 5 checkpoints started due
to wal pressure. There was no such wal-initiated checkpoint that
corresponds to the most recent WALWriteLock spike either.

Don.

--
Don Seiler
www.seiler.us