Re: ERROR: too many dynamic shared memory segments

On Wed, Jan 22, 2020 at 4:06 AM Nicola Contu <nicola(dot)contu(at)gmail(dot)com> wrote:
> after a few months, we started having this issue again.
> So we revert the work_mem parameter to 600MB instead of 2GB.
> But the issue is still there. A query went to segmentation fault, the DB went to recovery mode and our app went to read only for a few minutes.

Hi Nicola,
Hmm, a segmentation fault sounds like a different problem. Can you
please share the exact error messages from PostgreSQL and OS logs?

> I understand we can increase max_connections so we can have many more segments.
>
> My question is : is there a way to understand the number of segments we reached?

If you're on Linux, you can probably see them with "ls /dev/shm".

> Currently we have 220 max_conn so as your formula is 64 + 2* 220 we have about 500 shared segments.
> We would like to increase that number to 300 or 400 but would be great to understand if there is a way to make sure we will solve the issue as it requires a restart of the service.
>
> I know you were also talking about a redesign this part in PostgreSQL. Do you know if anything has changed in any of the newer versions after 11.5?

It's possible that we should increase a couple of constants used the
formula -- I'll look into that again. But first I'd like to see if
we're even investigating the right problem here.