Process memory reporting uses Erlang memory estimates by default

[jbaublitz]

This bug report is for version 3.6.12 of rabbitmq-server/rabbitmq-common.

This information was gathered using rabbitmqctl eval on the same RabbitMQ test server that showed performance issues under load.

There seems to be an issue in vm_memory_monitor:get_process_memory() where it actually reports erlang:memory(total) if the config option vm_memory_calculation_strategy is unset. As soon as this config option is set, the get_process_memory() function begins to report consistently with get_ps_memory(). However rabbitmqctl status does report that vm_memory_calculation_strategy is set to rss even when unset which is the default behavior but not consistent with the memory reporting values. In my glance at the code, this seems to mean that it is falling back on Erlang due to a ps output parsing issue but cannot verify this due to the function not being exported to the main application. Please let me know if you need any more information or would like me to test anything else.

[michaelklishin]

Thank you for your time.

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When/if we have enough details and evidence we'd be happy to file a new issue.

Thank you.

[michaelklishin]

The defaults are set in rabbitmq-server (via the rabbit.vm_memory_calculation_strategy key). You haven't provided any specific steps to reproduce but I have a node that includes #227 running with
mostly defaults and observe the following.

rabbit.vm_memory_calculation_strategy is what it is expected to be:

rabbitmqctl environment
 {rabbit,
      …
      {vm_memory_calculation_strategy,allocated}
      …

rabbitmqctl eval is not meant to be used for monitoring, so any side effects on it are considered to be a low priority for our team.

[michaelklishin]

Also:

rabbitmqctl eval "vm_memory_monitor:get_memory_calculation_strategy()."
allocated

So either #227 takes care of that on top of other things or I don't understand how to reproduce the issue.

[jbaublitz]

@michaelklishin I'm happy to provide steps to reproduce this but is that better suited for the mailing list? I'm a little confused because I was told to open an issue here.

[michaelklishin]

Yes. When/if we have enough details and conclude it is something that should be fixed, we will either update this issue or file a new one.

Our snapshot builds are currently not produced for unrelated reasons, so I don't think there is a snapshot that includes #227 but we can test the steps against a node running from source.

[gerhard]

@jbaublitz ping https://groups.google.com/d/msg/rabbitmq-users/Dw11uk9TPdc/-cgfkvTdAwAJ