a3kov

Atomic Bucket

Fast single node rate limiter implementing Token Bucket algorithm. The goal is to provide dependable solution that JustWorks™ with a focus on performance, correctness and ease of use. Bucket data is stored using :atomics module. Bucket references are stored in ETS and optionally cached as persistent terms.

Features

lock-free and race-free with compare-and-swap operations
BlazingFast™ performance, see benchmarks section in the readme. Req/s go brrrrrr
monotonic timer for correct calculations
millisecond tick supporting wider range of parameters and preventing request starvation
automatic calculation of bucket parameters based on target rate and burst size (for fixed cost requests)
handy timeouts for retries
support for token “refunds” and variable cost requests
compile-time validation of arguments when possible

Links

Package
Docs
Source

9 comments

#library #rate-limiting #rate-limiters #high-load #atomic_bucket

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2026-08-12 07:22:52 UTC

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Asd

This is a great library. The implementation is much more efficient and does not contain concurrency bugs like Hammer’s leaky bucket implementation.

Definitely gonna use it in one of my projects. One request is to leave the atomics ref management to the user!

Post #1

PJUllrich

Author of Building Table Views with Phoenix LiveView

TIL that :atomics exists great library and very interesting implementation! How did you learn about atomics and how did it lead to this library?

Post #2

a3kov

You have much more experience in Elixir than me so that is indeed strange.
In fact I’ve learned a lot from your blog posts in my Elixir journey.

It’s used in many libraries. Perhaps it’s a new trend to build stuff on top of it

Post #3

PJUllrich

Author of Building Table Views with Phoenix LiveView

Haha, thank you! I must now write a little blog post about atomics and will have to name you in it! That’s what you’re getting for sharing your good work online! Take that

Post #4

jsm

If you’re interested, this uses atomics as well: Once - Ecto type for globally unique 64-bits IDs generated by multiple Elixir nodes (to be precise, the underlying NoNoncense lib does).

Post #5

jsm

This is really cool

Post #6

a3kov

v0.1.3 fixes a stupid but nonetheless serious bug. Please update if you are using the library for anything important.

Post #7

a3kov

Version 0.2.0 comes with new advanced features via raw_request/5:

Support for variable request cost for cases where multiple operations have different cost, but share the same budget.
Support for negative cost (“token refunds”). Can be useful where an allowed operation failed and we don’t want it to “steal” the budget.

Unless some new ideas appear the library seems feature-complete at this point.

Post #8

a3kov

Version 0.3 is out with benchmarking improvements and perf. optimizations:

20-30% faster for buckets of normal size on 64bit
extremely big buckets and 32bit architectures will take a hit

Overall I think it’s a good trade-off - for now I don’t want to maintain 2 code paths and runtime checks would defeat the purpose. 64 bit and buckets typical for rate limiters is what most people use. This was a good case for me to learn about big integers on BEAM