Monitor Wish List (issue #10509)
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Low-hanging fruit
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* audit helpers that put() messages but do not get() them.
  where possible, get rid of those put().  No one expects helpers to
  put() messages and that may lead to double frees. (issue #9378)

Time consuming / complex
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* Split the OSDMonitor.cc file into auxiliary files.  This will mean:

  1. Logically split subsystems (osd crush, osd pool, ...)
  2. Split the big badass functions, especially prepare/process_command()

* Have Tracked Ops on the monitor, similarly to the OSDs. (issue #10507)

  1. Instead of passing messages back and forth, we will pass OpRequests
  2. We may be able to get() the message when we create the OpRequest and
     put() it upon OpRequest destruction.  This will help controlling the
     lifespan of messages and reduce leaks.
  3. There will be a fair amount of work changing stuff from Messages to
     OpRequests, and we will need to make sure that we reach a format that
     is easily supported throughout the monitor

  Possible format, off the top of my head:

    MonOpRequest:

      int op = m->get_type();
      Message *m = m.get();

      template<typename T>
      T* get_message() { return (T*)m.get(); }

* Move to Ref'erenced messages instead of pointers all around.  This would
  also help with the Tracked Ops thing, as we'd be able to simply ignore all
  the get() and put() stuff behind it. (issue #3500)

Delicate / complex
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* Finer-grained Paxos::is_readable() and/or PaxosService::is_readable()
  (issue #10508)

  Rationale: a given service S should be able to read its committed state
  even though a Paxos proposal is happening, as long as the on-going
  proposal is not a value of service S.