couch_stats

couch_stats is a simple statistics collection app for Erlang applications. Its core API is a thin wrapper around a stat storage library (currently Folsom,) but abstracting over that library provides several benefits:

• All references to stat storage are in one place, so it's easy to swap the module out.

• Some common patterns, such as tying a process's lifetime to a counter value, are straightforward to support.

• Configuration can be managed in a single place - for example, it's much easier to ensure that all histogram metrics use a 10-second sliding window if those metrics are instantiated/configured centrally.

Adding a metric

1. Write a stat description file. See `priv/descriptions.cfg for an example.

• The metric name should be of type [atom()].
• The type should be one of counter, gauge, or histogram.

If you don‘t add your metric to a description file, your metric will be accessible via couch_stats:sample/1, but it won’t be read by the stats collector and therefore won't be available to HTTP _stats requests, etc.

2. Tell couch_stats to use your description file via application configuration.

3. Instrument your code with the helper functions in couch_stats.erl.