Meta developer instruments: Working at scale

Every single day, hundreds of builders at Meta are working in repositories with hundreds of thousands of information. These builders want instruments that assist them at each stage of the workflow whereas working at excessive scale. On this article we’ll undergo a number of of the instruments within the growth course of. And, as an added bonus, these we discuss under are open supply so you possibly can attempt them your self.

Sapling: Scaling model management

Sapling is a model management system that may scale to large sizes, but in addition emphasizes usability. There are three major parts to Sapling – a server, a consumer, and a digital file system.

The server shops all the info and is a cautious mixture of intelligent storage codecs, wire protocols, and algorithms, largely carried out in Rust and architected to scale.

The consumer then talks to that server, offering all of the acquainted operations (try, rebase, commit, amend, and many others). As well as, the consumer can be able to speaking to a git server, which means that open supply GitHub repositories might be labored on utilizing our open-source Sapling release.

The ultimate element is the digital file system. When trying out a repository of our scale, simply the disk I/O of writing all of the information can take a major period of time. One resolution is sparse checkouts, the place a developer declares what subset of the repo they want to see upfront. A extra ergonomic various is EdenFS, which checks out the whole lot in a number of seconds however then solely really downloads the information from the server when they’re accessed.

Buck2: Construct system

After making modifications, many builders at Meta use Buck2 to compile the outcomes and take a look at out their modifications. Buck2 is designed to work at massive scale, supporting distant caching and execution, in order that builders can share one another’s compilations and a single developer can have entry to hundreds of machines to run compilations in parallel. Buck2 can be designed to assist a number of programming languages concurrently – so in order for you your OCaml program to rely on a Rust library that makes use of a C++ library whose supply code was generated by Erlang, that may work simply positive.

Buck2 works properly with out Sapling, however has particular design issues to allow Sapling and EdenFS. Buck2 makes use of Watchman to seek out out which information have modified, and Watchman helps EdenFS in order that it could combine easily with information that aren’t on the disk. Buck2 may use particular EdenFS operations to entry the file with out going through the disk, optimizing efficiency on methods the place digital file methods might be slower.

Infer, RacerD, and Jest: Testing and static evaluation

Handwritten exams and static evaluation play an essential function in ensuring all of our code features as supposed. Working with the amount of code we do at Meta signifies that we want instruments that present a high-quality sign, and accomplish that in a short time.

For basic static evaluation, we use a platform known as Infer, which is interprocedural and helps a number of languages, together with Java and C++. We even have extra tailored evaluation instruments akin to RacerD, which detects Java concurrency bugs. RacerD performed a giant function in our venture to transfer Fb’s Information Feed on Android from single-threaded to multi-threaded.

We even have language-specific testing frameworks. For instance, Jest is our Javascript testing framework. In 2022 we formally transferred Jest to the OpenJS Basis to additional assist its development inside the wider business.

Lastly, there are instruments that sit between static evaluation and guide take a look at circumstances. Our Sapienz software, for instance, robotically exams cell apps by permitting builders to simulate the person expertise to hunt out crashes and different potential points.

Study extra about Meta’s developer workflow

Along with our open-source instruments, our builders additionally use quite a lot of proprietary instruments of their day-to-day workflows as properly. For instance, Phabricator (Phab for brief), our CI and reviewing software, helps our builders evaluate and submit stacks of diffs. You will discover extra about these instruments (together with those lined above) within the article on Meta developer’s workflow.