Re: WALWriteLock

On Thu, Jul 8, 2021, 1:22 AM Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:

> On Tue, Jul 6, 2021 at 10:14 AM Yambu <hyambu(at)gmail(dot)com> wrote:
>
>> Hello
>>
>> I'm seeing a lot of WALWriteLocks , is this a bad sign , what might cause
>> this?
>>
>
> Are you having a performance problem you are trying to track down? If so,
> this probably indicates the cause. If not, then it is probably not a bad
> sign.
>
> The likely cause is that multiple sessions are trying to COMMIT at the
> same time, and are blocking on the slow fsync of the WAL data. One process
> will block on WALSync, all the ones queued up behind it will block on
> WALWrite.
>

Is this reproducible ? I mean I have seen multiple ppl raising a similar
issue but I could not really reproduce on my laptop, tried with slow disk,
introducing random latency etc. I even tried running gdb on a few processes
and trying to force into acquire a walwrite lock but not release it etc but
I guess I was not doing it correctly.

If the db is slowed down due to high concurrent usage trying to commit at
same time, how do we arrive at a baseline of how much a server can handle
before it starts tripping.

>