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Memory Mapped Stats Tools
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Mmstats is a way to expose and read ( diagnostic/statistical values for applications.

You could think of mmstats as /proc for your application and as one of the procps tools.


  • Separate publishing/writing from consuming/reading tools
  • Platform/language independent (a Java writer can be read by a Python tool)
  • Predictable performance impact for writers via:
    • No locks (1 writer per thread)
    • No syscalls
    • All in userspace
    • Reading has no impact on writers
  • Optional persistent (writer can sync anytime)
  • 1-way (Publish/consume only; mmstats are not management extensions)



CPython 2.6 or 2.7 (Windows is untested)

PyPy once issue869 is resolved.


  1. python install # Or copy into your project
  2. import mmstats
  3. Create a subclass of mmstats.MmStats like:
class WebStats(mmstats.MmStats):
    status2xx = mmstats.UIntField(label='status.2XX')
    status3xx = mmstats.UIntField(label='status.3XX')
    status4xx = mmstats.UIntField(label='status.4XX')
    status5xx = mmstats.UIntField(label='status.5XX')
  1. Instantiate it once per thread/process:
webstats = WebStats(label_prefix='web.stats.')
  1. Record some data:
if response.status_code == 200:
    webstats.status2xx += 1
  1. Run python to read it
  2. Run python to create a web interface for stats


  1. Run your favorite Python test runner (py.test or nosetests)
  2. Run
  3. Clean /tmp/mmstats-* files up

Data Structures

There are two types of data structures so far in mmstats:

  1. buffered
  2. unbuffered

Buffered structures use multiple buffers for handling values which cannot be written atomically.

Unbuffered structures have ff in the write buffer field.


label size label type size type write buffer buffers
ushort char[] ushort char[] byte varies

The buffers field length = sizeof(type) * buffers.

The current write buffer is referenced by: write_buffer * sizeof(type)

TODO: field for total number of buffers?


label size label type size type write buffer value
ushort char[] ushort char[] ff varies

The value field length = sizeof(type).

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