Local Metrics

This 0.0.1 is a candidate implementation. The API may change in 0.0.2.

Local metrics is a simple library for keeping application metrics locally.

It is a thin process facade on top of book-storage. v1 is counters and gauges. Every successful inc/set appends a sample. Prefer {folder, Path} as the persistent target.

{ok, Pid} = metrics_book:open({folder, "metrics"}),
ok = metrics_book:declare(Pid, http_requests, counter, [{labels, [method]}]),
ok = metrics_book:inc(Pid, http_requests, #{method => get}, 1),
{ok, 1} = metrics_book:value(Pid, http_requests, #{method => get}).

Written by the Erlangsters community and released under the MIT license.

Getting started

metrics_book:open/1 starts a linked gen_server that owns one book. Declare every metric on every start. Samples survive reopen; the declare table does not.

{ok, Pid} = metrics_book:open({folder, "metrics"}),
ok = metrics_book:declare(Pid, players, gauge),
ok = metrics_book:set(Pid, players, 12),
{ok, Samples} = metrics_book:query(Pid, #{name => players}),
ok = metrics_book:close(Pid).

Use {folder, Path} when the data should survive restart and stay bounded. Default max_pages is 32 on memory and folder. Use {file, Path} only as unbounded debug persist. Use memory in tests.

query/2 does not require declare and returns samples over time, oldest-first. stream/3 replies {ok, Ref}, then historical matches, then {metrics_book, Ref, live}, then later matching samples. A slow subscriber may see {overflow, N}. There is no durable cursor.

Callers who want a supervised book put {metrics_book, open, [Target, Options]} in their supervisor.

Installing the library

To use metrics-book in a rebar3 project, add it to your rebar.config.

{deps, [
  {metrics_book, {git, "https://github.com/erlangsters/metrics-book.git", {tag, "0.0.1"}}}
]}.