folsom
Folsom is an Erlang based metrics system inspired by Coda Hale's metrics (https://github.com/codahale/metrics/). The metrics API's purpose is to collect realtime metrics from your Erlang applications and publish them via Erlang APIs and output plugins. folsom is not a persistent store. There are 5 types of metrics, counters, gauges, histograms (and timers), histories and meters. Metrics can be created, read, and updated via the folsom_metrics module.
Building and running
First, regarding using folsom and folsom_webmachine together. To make sure you have compatible versions of each, make sure you use code from the same version tags, ie 0.5 of folsom is known to work with 0.5 folsom_webmachine. HEAD on each repo may have broken API compatibility.
You need a (preferably recent) version of Erlang installed but that should be it.
./rebar compile
folsom can be run standalone or embedded in an Erlang application.
$ erl -pa ebin
> folsom_sup:start_link(). % this creates the needed ETS tables and starts a gen_server
Metrics API
folsom_metrics.erl is the API module you will need to use most of the time.
Retreive a list of current installed metrics:
> folsom_metrics:get_metrics().
Query a specific metric:
> folsom_metrics:get_metric_value(Name).
Generally names of metrics are atoms or binaries.
Counters
Counter metrics provide increment and decrement capabilities for a single scalar value.
> folsom_metrics:new_counter(Name).
> folsom_metrics:notify({Name, {inc, Value}}).
> folsom_metrics:notify({Name, {dec, Value}}).
Gauges
Gauges are point-in-time single value metrics.
> folsom_metrics:new_gauge(Name).
> folsom_metrics:notify({Name, Value}).
Histograms (and Timers)
Histograms are collections of values that have statistical analysis done to them, such as mean, min, max, kurtosis and percentile. The can be used like "timers" as well with the timed update functions.
> folsom_metrics:new_histogram(Name).
> folsom_metrics:histogram_timed_update(Name, Mod, Fun, Args).
> folsom_metrics:histogram_timed_update(Name, Fun, Args).
> folsom_metrics:histogram_timed_update(Name, Fun).
> folsom_metrics:notify({Name, Value}).
Histories
Histories are a collection of past events, such as errors or log messages.
> folsom_metrics:new_history(Name).
> folsom_metrics:get_history_values(Name, Count). % get more than the default number of history items back
> folsom_metrics:notify({Name, Value}).
Meters
Meters are increment only counters with mean rates and exponentially weighted moving averages applied to them, similar to a unix load average.
> folsom_metrics:new_meter(Name).
> folsom_metrics:notify({Name, Value}).
Erlang VM
folsom also produces Erlang VM statistics.
The result of erlang:memory/0:
> folsom_vm_metrics:get_memory().
The result of erlang:system_info/1:
> folsom_vm_metrics:get_system_info().
The result of erlang:statistics/1:
> folsom_vm_metrics:get_statistics().
The result of erlang:process_info/1:
> folsom_vm_metrics:get_process_info(). %% use with caution
The result of inet:getstat/1, prim_inet:getstatus/1, erlang:port_info/1, prim_inet:gettype/1, inet:getopts/1, inet:sockname/1:
> folsom_vm_metrics:get_port_info(). %% use with caution