[SR-Users] Meaning of shmem stats and question on dmq dialog sharing behaviour

[George Diamantopoulos]

Hello all,

I've recently been experimenting with dmq, and I've noticed something that
seemed a little odd. shmem use would often be abnormally high on otherwise
idle kamailio nodes (literally, only dispatcher module OPTIONS were
exchanged at the time besides KDMQ messages).

After disabling the "enable_dmq" parameter for the dialog module, this sort
of absurd behaviour ceased. To get a quantified idea of this change's
effect, check out the following screenshot from our monitoring system:
https://pasteboard.co/Jb430lD.png

As you can see, the spikes stopped manifesting at around 05:00, when dmq
was disabled for dialog (albeit still employed for htable). shmem use then
grew as traffic was introduced to these nodes, and htables began filling
with data.

I was wondering if this to be expected, which I find highly odd given that
at the time other productive systems in the DMQ cluster were also idle
(given the time of the day), not to mention that their shmem usage was not
nearly as high.

Could this be attributed to some configuration error, with updates looping
endlessly (or until some counter reaches zero or something) among nodes? Or
could memory be used for other housekeeping purposes unrelated to dmq
dialog sharing?

Lastly, what is the meaning (and differences) of these shmem stats?

   - real_used_size
   - used_size
   - max_used_size

Max used size I get (I'm guessing maximum seen since server was started?)
but what's the difference between real_used and used? Thanks!

Best regards,
George
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