[erlang-patches] erlang:system_monitor long_message_queue

Michał Ptaszek <>
Tue Dec 10 01:05:03 CET 2013

Hey All,


This patch adds a new option to the erlang:system_monitor BIF, allowing to
subscribe monitor process to the long_message_queue events. It should be
really helpful when investigating architectural bottlenecks, as well as a
part of regular logging procedures.

Few comments about the implementation:
- Monitor messages are generated once the message gets appended to the
receiver's message queue.
- For a certain process - monitor message can be generated only once after
exceeding a pre-configured threshold. Erlang VM will resend the monitor
message only once the process mailbox size gets below the limit and exceeds
them again.
- Info list of the monitor message currently contains only receiver's
message queue length. If you have any ideas on what might be useful to put
there in addition to the mailbox size - please let me know.

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