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Structured telemetry library for Clojure/Script

Telemere is a next-generation replacement for Timbre. It handles structured and traditional logging, tracing, and basic performance monitoring with a simple unified API.

It helps enable Clojure/Script systems that are observable, robust, and debuggable - and it represents the refinement and culmination of ideas brewing over 12+ years in Timbre, Tufte, Truss, etc.

[Terminology] Telemetry derives from the Greek tele (remote) and metron (measure). It refers to the collection of in situ (in position) data, for transmission to other systems for monitoring/analysis. Logs are the most common form of software telemetry. So think of telemetry as the superset of logging-like activities that help monitor and understand (software) systems.

Latest release/s

• v1.0.0-beta2: release info

See here for earlier releases.

Why Telemere?

Ergonomics

• Elegant, lightweight API that's easy to use, easy to configure, and deeply flexible.
• Sensible defaults to make getting started fast and easy.
• Extensive beginner-oriented documentation, docstrings, and error messages.

Interop

• 1st-class out-the-box interop with SLF4J v2, clojure.tools.logging, OpenTelemetry, and Tufte.
• Included shim for easy/gradual migration from Timbre.

Scaling

• Hyper-optimized and blazing fast, see benchmarks.
• An API that scales comfortably from the smallest disposable code, to the most massive and complex real-world production environments.

Flexibility

• Config via plain Clojure vals and fns for easy customization, composition, and REPL debugging.
• Unmatched support for system-level config (JVM props, ENV vars, classpath resources).
• Expressive per-call and per-handler filtering at both runtime and compile-time.
• Filter by namespace and id pattern, level, level by namespace pattern, etc.
• Sampling, rate-limiting, and back-pressure monitoring.
• Fully configurable a/sync dispatch (blocking, dropping, sliding, etc.).

Video demo

See for intro and usage:

Quick examples

(require '[taoensso.telemere :as t])

;; Start simple
(t/log! "This will send a `:log` signal to the Clj/s console")
(t/log! :info "This will do the same, but only when the current level is >= `:info`")

;; Easily construct messages
(let [x "constructed"] (t/log! :info ["Here's a" x "message!"]))

;; Attach an id
(t/log! {:level :info, :id ::my-id} "This signal has an id")

;; Attach arb user data
(t/log! {:level :info, :data {:x :y}} "This signal has structured data")

;; Capture for debug/testing
(t/with-signal (t/log! "This will be captured"))
;; => {:keys [location level id data msg_ ...]}

;; `:let` bindings available to `:data` and message, only paid for
;; when allowed by minimum level and other filtering criteria
(t/log!
  {:level :info
   :let [expensive-metric1 (last (for [x (range 100), y (range 100)] (* x y)))]
   :data {:metric1 expensive-metric1}}
  ["Message with metric value:" expensive-metric1])

;; With sampling 50% and 1/sec rate limiting
(t/log!
  {:sample-rate 0.5
   :rate-limit  {"1 per sec" [1 1000]}}
  "This signal will be sampled and rate limited")

;;; A quick taste of filtering...

(t/set-ns-filter! {:deny "taoensso.*" :allow "taoensso.sente.*"}) ; Set namespace filter
(t/set-id-filter! {:allow #{::my-particular-id "my-app/*"}})      ; Set id        filter

(t/set-min-level!       :warn) ; Set minimum level
(t/set-min-level! :log :debug) ; Set minimul level for `:log` signals

;; Set minimum level for `:event` signals originating in the "taoensso.sente.*" ns
(t/set-min-level! :event "taoensso.sente.*" :warn)

See examples.cljc for more REPL-ready snippets.

API overview

See relevant docstrings (links below) for usage info-

Signal creators

Name	Signal kind	Main arg	Optional arg	Returns
log!	:log	msg	opts/level	Signal allowed?
event!	:event	id	opts/level	Signal allowed?
error!	:error	error	opts/id	Given error
trace!	:trace	form	opts/id	Form result
spy!	:spy	form	opts/level	Form result
catch->error!	:error	form	opts/id	Form value or given fallback
signal!	<arb>	opts	-	Depends on opts

Signal filters

Global	Dynamic	Filters by
set-kind-filter!	with-kind-filter	Signal kind (:log, :event, etc.)
set-ns-filter!	with-ns-filter	Signal namespace
set-id-filter!	with-id-filter	Signal id
set-min-level	with-min-level	Signal level (minimum can be specified by kind and/or ns)

Internal help

Var	Help with
help:signal-creators	List of signal creators
help:signal-options	Options for signal creators
help:signal-content	Signal map content
help:signal-flow	Ordered flow from signal creation to handling
help:signal-filters	API for configuring signal filters
help:signal-handlers	API for configuring signal handlers
help:signal-formatters	Signal formatters for use by handlers

Example handler output

(t/log! {:id ::my-id, :data {:x1 :x2}} "My message") =>

Clj console handler

String output:

2024-04-11T10:54:57.202869Z INFO LOG Schrebermann.local examples(56,1) ::my-id - My message
    data: {:x1 :x2}

Cljs console handler

Chrome console:

Cljs raw console handler

Chrome console, with cljs-devtools:

Clj file handler

MacOS terminal:

Documentation

• Wiki (getting started, usage, etc.)
• API reference: cljdoc or Codox
• Support: Slack channel or GitHub issues

Observability tips

See here for general advice re: building and maintaining observable Clojure/Script systems.

Benchmarks

Telemere is highly optimized and offers terrific performance at any scale:

Compile-time filtering?	Runtime filtering?	Time?	Trace?	nsecs
✓ (elide)	-	-	-	0
-	✓	-	-	200
-	✓	✓	-	280
-	✓	✓	✓	650

Measurements:

• Are ~nanoseconds per signal call (= milliseconds per 1e6 calls)
• Exclude handler runtime (which depends on handler/s, is usually async)
• Taken on a 2020 Macbook Pro M1, running OpenJDK 21

Tip: Telemere offers extensive per-call and per-handler filtering, sampling, and rate-limiting. Use these to ensure that you're not capturing useless/low-value information in production. See here for more tips!

Funding

You can help support continued work on this project, thank you!! 🙏

License

Copyright © 2023-2024 Peter Taoussanis.
Licensed under EPL 1.0 (same as Clojure).