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It looks like we need to update the documentation at the top of Counter to 
reflect that we intentionally left out decrementing, because we found that some 
metrics libraries and systems have a counter type that only supports going up 
or potentially being reset to 0. For example:

http://lymph.readthedocs.org/en/latest/api/metrics_api.html#lymph.core.monitoring.metrics.Counter
https://prometheus.io/docs/concepts/metric_types/#counter
https://blog.pkhamre.com/understanding-statsd-and-graphite/

Think of a counter as something that just counts events that go by, in which 
context decrementing doesn't apply. If we want this decrementing behavior, we 
probably want to distinguish it with a new type of Metric. This is because 
users have asked for the ability to distinguish different metric types (e.g. 
counter vs gauge) because some monitoring systems need to be told whether it 
can be decremented.

Make sense?

- Ben Mahler


On March 9, 2016, 7:07 p.m., Cong Wang wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/44473/
> -----------------------------------------------------------
> 
> (Updated March 9, 2016, 7:07 p.m.)
> 
> 
> Review request for mesos, Ben Mahler, Ian Downes, Vinod Kone, and Jiang Yan 
> Xu.
> 
> 
> Bugs: MESOS-4740
>     https://issues.apache.org/jira/browse/MESOS-4740
> 
> 
> Repository: mesos
> 
> 
> Description
> -------
> 
> Added decrement operator to Counter.
> 
> 
> Diffs
> -----
> 
>   3rdparty/libprocess/include/process/metrics/counter.hpp 
> a13cc7e18c8b23eae83c326d63874d9d2aaedc0d 
>   3rdparty/libprocess/src/tests/metrics_tests.cpp 
> b84dc8d858f58bc9f52b218b7153510417cf34c2 
> 
> Diff: https://reviews.apache.org/r/44473/diff/
> 
> 
> Testing
> -------
> 
> make check
> 
> 
> Thanks,
> 
> Cong Wang
> 
>

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