Current semantic version:

[com.taoensso/timbre "2.0.0"] ; See commit history for breaking changes since 1.x

Timbre, a (sane) Clojure logging & profiling library

Logging with Java can be maddeningly, unnecessarily hard. Particularly if all you want is something simple that works out-the-box. Timbre is an attempt to make simple logging simple and more complex logging reasonable. No XML!

What's in the box™?

• Small, uncomplicated all-Clojure library.
• Super-simple map-based config: no arcane XML or properties files!
• Decent performance (low overhead).
• Flexible fn-centric appender model with middleware.
• Sensible built-in appenders including simple email appender.
• Tunable rate limit and asynchronous logging support.
• Robust namespace filtering.
• tools.logging support (optional).
• Dead-simple, logging-level-aware logging profiler.

Getting started

Dependencies

Add the necessary dependency to your Leiningen project.clj and require the library in your ns:

[com.taoensso/timbre "2.0.0"] ; project.clj
(ns my-app (:require [taoensso.timbre :as timbre
                      :refer (trace debug info warn error fatal spy)])) ; ns

Logging

By default, Timbre gives you basic print output to *out*/*err* at a debug logging level:

(info "This will print")
=> nil
%> 2012-May-28 17:26:11:444 +0700 localhost INFO [my-app] - This will print

(spy :info (* 5 4 3 2 1))
=> 120
%> 2012-May-28 17:26:14:138 +0700 localhost INFO [my-app] - (* 5 4 3 2 1) 120

(trace "This won't print due to insufficient logging level")
=> nil

There's little overhead for checking logging levels:

(time (trace (Thread/sleep 5000)))
%> "Elapsed time: 0.054 msecs"

(time (when false))
%> "Elapsed time: 0.051 msecs"

First-argument exceptions generate a stack trace:

(info (Exception. "Oh noes") "arg1" "arg2")
%> 2012-May-28 17:35:16:132 +0700 localhost INFO [my-app] - arg1 arg2
java.lang.Exception: Oh noes
            NO_SOURCE_FILE:1 my-app/eval6409
          Compiler.java:6511 clojure.lang.Compiler.eval
          <...>

Configuration

Configuring Timbre couldn't be simpler. Let's check out (some of) the defaults:

@timbre/config
=>
{:current-level :debug

 :ns-whitelist []
 :ns-blacklist []

 :middleware [] ; As of Timbre 1.4.0, see source for details

 :timestamp-pattern "yyyy-MMM-dd HH:mm:ss ZZ"
 :timestamp-locale  nil

 :appenders
 {:standard-out        { <...> }
  :spit                { <...> }
  <...> }

 :shared-appender-config {}}

Easily adjust the current logging level:

(timbre/set-level! :warn)

And the default timestamp formatting for log messages:

(timbre/set-config! [:timestamp-pattern] "yyyy-MMM-dd HH:mm:ss ZZ")
(timbre/set-config! [:timestamp-locale] (java.util.Locale/GERMAN))

Filter logging output by namespaces:

(timbre/set-config! [:ns-whitelist] ["some.library.core" "my-app.*"])

Built-in appenders

File appender

(timbre/set-config! [:appenders :spit :enabled?] true)
(timbre/set-config! [:shared-appender-config :spit-filename] "/path/my-file.log")

Email (Postal) appender

;; [com.draines/postal "1.9.2"] ; Add to project.clj dependencies
;; (:require [taoensso.timbre.appenders (postal :as postal-appender)]) ; Add to ns

(timbre/set-config! [:appenders :postal] postal-appender/postal-appender)
(timbre/set-config! [:shared-appender-config :postal]
                    ^{:host "mail.isp.net" :user "jsmith" :pass "sekrat!!1"}
                    {:from "me@draines.com" :to "foo@example.com"})

;; Rate limit to one email per message per minute
(timbre/set-config! [:appenders :postal :limit-per-msecs] 60000)

;; Make sure emails are sent asynchronously
(timbre/set-config! [:appenders :postal :async?] true)

IRC (irclj) appender

;; [irclj "0.5.0-alpha2"] ; Add to project.clj dependencies
;; (:require [taoensso.timbre.appenders (irc :as irc-appender)]) ; Add to ns

(timbre/set-config! [:appenders :irc] irc-appender/irc-appender)
(timbre/set-config! [:shared-appender-config :irc]
                    {:host "irc.example.org"
                     :port 6667
                     :nick "logger"
                     :name "Logger"
                     :chan "#logs"})

Custom appenders

Writing a custom appender is dead-easy:

(timbre/set-config!
 [:appenders :my-appender]
 {:doc       "Hello-world appender"
  :min-level :debug
  :enabled?  true
  :async?    false
  :limit-per-msecs nil ; No rate limit
  :fn (fn [{:keys [ap-config level prefix throwable message] :as args}]
        (when-not (:my-production-mode? ap-config)
          (println prefix "Hello world!" message)))

And because appender fns are just regular Clojure fns, you have unlimited power: write to your database, send a message over the network, check some other state (e.g. environment config) before making a choice, etc.

See the timbre/config docstring for more information on appenders.

Profiling

The usual recommendation for Clojure profiling is: use a good JVM profiler like YourKit, JProfiler, or VisualVM.

And these certainly do the job. But as with many Java tools, they can be a little hairy and often heavy-handed - especially when applied to Clojure. Timbre includes an alternative.

Let's add it to our app's ns declaration:

(:require [taoensso.timbre.profiling :as profiling :refer (p profile)])

Wrap forms that you'd like to profile with the p macro and give them a name:

(defn my-fn
  []
  (let [nums (vec (range 1000))]
    (+ (p :fast-sleep (Thread/sleep 1) 10)
       (p :slow-sleep (Thread/sleep 2) 32)
       (p :add  (reduce + nums))
       (p :sub  (reduce - nums))
       (p :mult (reduce * nums))
       (p :div  (reduce / nums)))))

(my-fn)
=> 42

The profile macro can now be used to log times for any wrapped forms:

(profile :info :Arithmetic (dotimes [n 100] (my-fn)))
=> "Done!"
%> 2012-Jul-03 20:46:17 +0700 localhost INFO [my-app] - Profiling my-app/Arithmetic
              Name  Calls       Min        Max       MAD      Mean  Total% Total
 my-app/slow-sleep    100       2ms        2ms      31μs       2ms      57 231ms
 my-app/fast-sleep    100       1ms        1ms      27μs       1ms      29 118ms
        my-app/add    100      44μs        2ms      46μs     100μs       2 10ms
        my-app/sub    100      42μs      564μs      26μs      72μs       2 7ms
        my-app/div    100      54μs      191μs      17μs      71μs       2 7ms
       my-app/mult    100      31μs      165μs      11μs      44μs       1 4ms
       Unaccounted                                                       6 26ms
             Total                                                     100 405ms

It's important to note that Timbre profiling is fully logging-level aware: if the level is insufficient, you won't pay for profiling. Likewise, normal namespace filtering applies. (Performance characteristics for both checks are inherited from Timbre itself).

And since p and profile always return their body's result regardless of whether profiling actually happens or not, it becomes feasible to use profiling more often as part of your normal workflow: just leave profiling code in production as you do for logging code.

A simple sampling profiler is also available: taoensso.timbre.profiling/sampling-profile.

Project links

• API documentation.
• My other Clojure libraries (Redis & DynamoDB clients, logging+profiling, I18n+L10n, serialization, A/B testing).

This project supports the CDS and ClojureWerkz project goals:

• CDS, the Clojure Documentation Site, is a contributer-friendly community project aimed at producing top-notch Clojure tutorials and documentation.

• ClojureWerkz is a growing collection of open-source, batteries-included Clojure libraries that emphasise modern targets, great documentation, and thorough testing.

Contact & contribution

Please use the project's GitHub issues page for project questions/comments/suggestions/whatever (pull requests welcome!). Am very open to ideas if you have any!

Otherwise reach me (Peter Taoussanis) at taoensso.com or on Twitter (@ptaoussanis). Cheers!

License

Copyright © 2012, 2013 Peter Taoussanis. Distributed under the Eclipse Public License, the same as Clojure.