6 FAQ

Does Telemere replace Timbre?

Timbre is a pure Clojure/Script logging library, and ancestor of Telemere.

Yes, Telemere's functionality is a superset of Timbre, and offers many improvements over Timbre.

But Timbre will continue to be maintained and supported, and will even receive some backwards-compatible improvements back-ported from Telemere.

There is no pressure to migrate if you'd prefer not to.

See section 5-Migrating for migration info.

Why not just update Timbre?

Timbre is a pure Clojure/Script logging library, and ancestor of Telemere.

Why release Telemere as a new library instead of just updating Timbre?

Timbre was first released 12+ years ago, and has mostly attempted to keep breaks in that time minimal. Which means that its fundamental design is now 12+ years old.

I've learnt a lot since then, and would write Timbre differently if I were doing it again today. There's many refinements I've wanted to make over the years, but held back both because of the effort involved and because of not wanting to break Timbre users that are happy with it the way it is.

Since receiving open source funding, undertaking larger projects became feasible - so I decided to experiment with a proof-of-concept rewrite free of all historical constraints.

That eventually grew into Telemere. And I'm happy enough with the result that I feel confident in saying that there's nothing Timbre does better than Telemere, but plenty that Telemere does better than Timbre. Telemere is easier to use, faster, more robust, and significantly more flexible. It offers a better platform for what will be (I hope) the next many years of service.

I will continue to maintain and support Timbre for users that are happy with it, though I've also tried to make migration as easy as possible.

Over time, I also intend to back-port many backwards-compatible improvements from Telemere to Timbre. For one, Telemere's core was actually written as a library that will eventually be used by Telemere, Timbre, and also Tufte.

This will eventually ease long-term maintenance, increase reliability, and help provide unified capabilities across all 3.

Does Telemere replace Tufte?

Tufte is a simple performance monitoring library for Clojure/Script by the author of Telemere.

No, Telemere does not replace Tufte. They work great together, and the upcoming Tufte v3 will share the same core as Telemere and offer an identical API for managing filters and handlers.

There is some feature overlap though since Telemere offers basic performance measurement as part of its tracing features.

For comparison:

• Telemere offers dynamic profiling of a single form to a simple :runtime-nsecs.
• Tufte offers dynamic and thread-local profiling of arbitrary nested forms to detailed and mergeable runtime stats.

Basically, Tufte has much richer performance monitoring capabilities.

They're focused on complementary things. When both are in use:

• Tufte can be used for detailed performance measurement, and
• Telemere can be used for conveying (aggregate) performance information as part of your system's general observability signals.

Does Telemere work with GraalVM?

GraalVM is a JDK alternative with ahead-of-time compilation for faster app initialization and improved runtime performance, etc.

Yes, this shouldn't be a problem.

Does Telemere work with Babashka?

Babashka is a native Clojure interpreter for scripting with fast startup.

No, not currently - though support should be possible with a little work. The current bottleneck is a dependency on Encore, though that could actually be removed (also offering benefits re: library size).

If there's interest in this, please upvote on my open source roadmap.

Why no format-style messages?

Telemere's message API can do everything that traditional print or format style message builders can do but much more flexibly - and with pure Clojure/Script (so no arcane pattern syntax).

To coerce/format/prepare args, just use the relevant Clojure/Script utils.

Signal messages are always lazy (as are a signal's :let and :data options), so you only pay the cost of arg prep and message building if/when a signal is actually created (i.e. after filtering, sampling, rate limiting, etc.).

Examples:

;; A fixed message (string arg)
(t/log! "A fixed message") ; %> {:msg "A fixed message"}

;; A joined message (vector arg)
(let [user-arg "Bob"]
  (t/log! ["User" (str "`" user-arg "`") "just logged in!"]))
;; %> {:msg_ "User `Bob` just logged in!` ...}

;; With arg prep
(let [user-arg "Bob"
      usd-balance-str "22.4821"]

  (t/log!
    {:let
     [username (clojure.string/upper-case user-arg)
      usd-balance (parse-double usd-balance-str)]

     :data
     {:username    username
      :usd-balance usd-balance}}

    ["User" username "has balance:" (str "$" (Math/round usd-balance))]))

;; %> {:msg "User BOB has balance: $22" ...}

(t/log! (str "This message " "was built " "by `str`"))
;; %> {:msg "This message was built by `str`"}

(t/log! (format "This message was built by `%s`" "format"))
;; %> {:msg "This message was built by `format`"}

Note that you can even use format or any other formatter/s of your choice. Your signal message is the result of executing code, so build it however you want.

See also msg-skip and msg-splice for some handy utils.

How to use Telemere from a library?

See section 9-Authors.

How does Telemere compare to Mulog?

Mulog is an excellent "micro-logging library" for Clojure that shares many of the same capabilities and objectives as Telemere.

Some similarities between Telemere and Mulog:

• Both emphasize structured data rather than string messages
• Both offer tracing to understand (nested) program flow
• Both offer a (nested) context mechanism for arb application state
• Both are fast and offer async handling
• Both offer a variety of handlers and are designed for ease of use

Some particular strengths of Mulog that I'm aware of:

• More established/mature
• Wider range of handlers (incl. Kafka, Kinesis, Prometheus, Zipkin, etc.)
• More community resources (videos, guides, users, etc.)
• Smaller code base (Telemere currently depends on Encore)
• There may be others!

Some particular strengths of Telemere:

• Both Clj and Cljs support (Mulog is Clj only)
• Rich filtering capabilities (see help:filters) incl. compile-time elision
• Rich dispatch control (see help:handler-dispatch-options)
• Rich environmental config (see help:environmental-config) for all platforms
• Detailed handler stats (see get-handlers-stats)
• Single unified API for all telemetry and traditional logging needs (see help:signal-creators)
• Lazy :let, :data, :msg, :do - evaluated only after filtering
• Extensive in-IDE documentation

My subjective thoughts:

Mulog is an awesome, well-designed library with quality documentation and a solid API. It's absolutely worth checking out - you may well prefer it to Telemere!

The two libraries have many shared capabilities and objectives.

Ultimately I wrote Telemere because:

1. I have some particular needs, including very complex and large-scale applications that benefit from the kind of flexibility that Telemere offers re: filtering, dispatch, environmental config, lazy (post-filter) evaluation, etc.
2. I have some particular tastes re: my ideal API.
3. I wanted something that integrated particularly well with Tufte and could share an identical API for filtering, handlers, etc.
4. I wanted a modern replacement for Timbre users that offered a superset of its functionality and an easy migration path.

Other questions?

Please open a Github issue or ping on Telemere's Slack channel. I'll regularly update the FAQ to add common questions. - Peter