telemere/README.md

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# Telemere

### Structured telemetry library for Clojure/Script

**Telemere** is a next-generation replacement for [Timbre](https://www.taoensso.com/timbre). It handles **structured and traditional logging**, **tracing**, and **basic performance monitoring** with a simple unified API.

It helps enable the creation of Clojure/Script systems that are highly **observable**, **robust**, and **debuggable** - and it represents the refinement and culmination of ideas brewing over 12+ years in [Timbre](https://github.com/taoensso/timbre), [Tufte](https://github.com/taoensso/tufte), [Truss](https://github.com/taoensso/truss), etc.

> [Terminology] *Telemetry* is derived from the Greek roots *tele* (remote) and *metron* (measure). It refers to the collection of *in situ* (in position) information, 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

> This library is still under development, ETA: [end April 2024](https://www.taoensso.com/roadmap).

- `v1.0.0-alpha4` (dev): [release info](https://clojars.org/com.taoensso/telemere/versions/1.0.0-alpha4) (for early adopters)

[![Main tests][Main tests SVG]][Main tests URL]
[![Graal tests][Graal tests SVG]][Graal tests URL]

See [here][GitHub releases] 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][GitHub wiki], [docstrings](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso), and error messages.

#### Interop

- 1st-class **out-the-box interop** with [SLF4J v2](https://www.slf4j.org/), [clojure.tools.logging](https://github.com/clojure/tools.logging), [OpenTelemetry](https://opentelemetry.io/), and [Tufte](https://www.taoensso.com/tufte) (soon).
- Included shim for easy/gradual [migration from Timbre](../../wiki/7-Migrating).

#### Scaling

- Hyper-optimized and **blazing fast**, see [benchmarks](#performance).
- 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 **environmental config** (JVM props, ENV vars, edn resources, etc.).
- 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:

**TODO**: soon

<!--
<a href="https://www.youtube.com/watch?v=TODO" target="_blank">
 <img src="https://img.youtube.com/vi/TODO/maxresdefault.jpg" alt="Telemere demo video" width="480" border="0" />
</a> -->

## Quick examples

```clojure
(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)
```

## API overview

See links below for docstrings/usage, and [documentation](#documentation) for lots more info.

### Signal creators

| Name | Signal kind | Main arg | Optional arg | Returns
:-- | :-- | :-- | :-- | :--
| [`signal!`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#signal!) | `<arb>` | `opts` | - | Signal allowed? / form result (value or throw)
| [`log!`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#log!) | `:log` | `msg` | `opts`/`level` | Signal allowed?
| [`event!`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#event!) | `:event` | `id` | `opts`/`level` | Signal allowed?
| [`error!`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#error!) | `:error` | `error` | `opts`/`id` | Given error
| [`trace!`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#trace!) | `:trace` | `form` | `opts`/`id` | Form result
| [`spy!`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#spy!) | `:spy` | `form` | `opts`/`level` | Form result
| [`catch->error!`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#catch-%3Eerror!) | `:error` | `form` | `opts`/`id` | Form value or given fallback

### Signal filters

| Global | Dynamic | Filters by
| :-- | :-- | :--
| [`set-kind-filter!`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#set-kind-filter!) | [`with-kind-filter`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#with-kind-filter) | Signal kind (`:log`, `:event`, etc.)
| [`set-ns-filter!`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#set-ns-filter!) | [`with-ns-filter`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#with-ns-filter) | Signal namespace
| [`set-id-filter!`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#set-id-filter!) | [`with-id-filter`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#with-id-filter) | Signal id
| [`set-min-level`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#set-min-level) | [`with-min-level`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#with-min-level) | Signal level (minimum can be specified by kind and/or ns)

### Internal help

Telemere includes extensive internal help docstrings:

| Var | Help with
| :-- | :--
| [`help:signal-options`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#help:signal-options) | Options for standard signal creators
| [`help:signal-content`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#help:signal-content) | Content of signal maps
| [`help:signal-flow`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#help:signal-flow) | Ordered flow from signal creation to handling
| [`help:signal-filters`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#help:signal-filters) | API for configuring signal filters
| [`help:signal-handlers`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#help:signal-handlers) | API for configuring signal handlers
| [`help:signal-formatters`](https://cljdoc.org/d/com.taoensso/telemere/CURRENT/api/taoensso.telemere#help:signal-formatters) | Signal formatters for use by handlers

### Example handler output

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

##### Default Clojure console handler:

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

##### Default ClojureScript console handler in Chrome:

<img src="/imgs/handler-output-cljs-console.png" alt="Default ClojureScript console handler output" width="640"/>

##### Raw ClojureScript console handler in Chrome, with [cljs-devtools](https://github.com/binaryage/cljs-devtools):

<img src="/imgs/handler-output-cljs-console-raw.png" alt="Raw ClojureScript console handler output" width="640"/>

##### Default Clojure file handler in MacOS terminal:

<img src="/imgs/handler-output-clj-file.png" alt="Default Clojure file handler output" width="640"/>

## Documentation

- [Wiki][GitHub wiki] (getting started, usage, etc.) (**TODO:** soon)
- API reference: [cljdoc][cljdoc docs], [Codox][Codox docs]

## Observability tips

See [here](/../../wiki/8-Tips) 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](/TODO) for more tips!

## Funding

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

## License

Copyright &copy; 2023-2024 [Peter Taoussanis][].  
Licensed under [EPL 1.0](LICENSE.txt) (same as Clojure).

<!-- Common -->

[GitHub releases]: ../../releases
[GitHub issues]:   ../../issues
[GitHub wiki]:     ../../wiki

[Peter Taoussanis]: https://www.taoensso.com
[sponsor]:          https://www.taoensso.com/sponsor

<!-- Project -->

[Codox docs]:   https://taoensso.github.io/telemere/
[cljdoc docs]: https://cljdoc.org/d/com.taoensso/telemere/

[Clojars SVG]: https://img.shields.io/clojars/v/com.taoensso/telemere.svg
[Clojars URL]: https://clojars.org/com.taoensso/telemere

[Main tests SVG]:  https://github.com/taoensso/telemere/actions/workflows/main-tests.yml/badge.svg
[Main tests URL]:  https://github.com/taoensso/telemere/actions/workflows/main-tests.yml
[Graal tests SVG]: https://github.com/taoensso/telemere/actions/workflows/graal-tests.yml/badge.svg
[Graal tests URL]: https://github.com/taoensso/telemere/actions/workflows/graal-tests.yml