The Linux kernel is a prominent example of a large open source software repository containing approximately 15 million lines of code in 40,000 files.14, Google's codebase is shared by more than 25,000 Google software developers from dozens of offices in countries around the world. In Companion to the 21st ACM SIGPLAN Symposium on Object-Oriented Programming Systems, Languages, and Applications (Portland, OR, Oct. 22-26). To prevent dependency conflicts, as outlined earlier, it is important that only one version of an open source project be available at any given time. CitC workspaces are available on any machine that can connect to the cloud-based storage system, making it easy to switch machines and pick up work without interruption. cases Bazel should be used. Because all projects are centrally stored, teams of specialists can do this work for the entire company, rather than require many individuals to develop their own tools, techniques, or expertise. a. Most developers can view and propose changes to files anywhere across the entire codebasewith the exception of a small set of highly confidential code that is more carefully controlled. There is a tension between consistent style and tool use with freedom and flexibility of the toolchain. Should you have the same deep pocket and engineering fire power as Google, you could probably build the missing tools for making it work across multiple repos (for example, adequate search across many repos, or applying patches and running tests a group of repos instead of a single repo). The ability to distribute a command across many machines, while largely preserving the dev ergonomics of running it on a single machine. Updating is difficult when the library callers are hosted in different repositories. - My understanding is that Google services are compiled&deployed from trunk; what does this mean for database migrations (e.g., schema upgrades), in particular when different instances of the same service are maintained by different teams: How do you coordinate such distributed data migrations in the face of more or less continuous upgrades of binaries? The monolithic codebase captures all dependency information. And let's not get started on reconciling incompatible versions of third party libraries across repositories No one wants to go through the hassle of setting up a shared repo, so teams just write their own implementations of common services and components in each repo. - Similarly, when a service is deployed from today's trunk, but a dependent service is still running on last week's trunk, how is API compatibility guaranteed between those services? sign in They are used only for release branches, An important point is that both old and new code path for any new features exist simultaneously, controlled by the use of conditional flags, allowing for smoother deployments and avoiding the need for development branches, 1- unified versioning, one source of truth, 1.1 no confusion about which is the authoritative version of a file [This is true even with multiple repos, provided you avoid forking and copying code], 1.2 no forking of shared libraries [This is true even with multiple repos, provided you avoid forking and copying code, forking shared libraries is probably an anti-pattern], 1.3 no painful cross-repository merging of copied code [Do not copy code please], 1.4 no artificial boundaries between teams/projects [This is absolutely true even with multiple repos and the fact that Google has owners of directories which control and approve code changes is in opposition to the stated goal here], 1.5 supports gradual refactoring and re-organisation of the codebase [This is indeed made easier by a mono-repo, but good architecture should allow for components to be refactored without breaking the entire code base everywhere], 2. extensive code sharing and reuse [This is not related to the mono-repo], 3. simplified dependency management [Probably, though debatable], 3.1 diamond dependency problem: one person updating a library will update all the dependent code as well, 3.2 Google statically links everything (yey! Determine what might be affected by a change, to run only build/test affected projects. Find better developer tools for sgeb will then build and invoke this builder for them. Use Git or checkout with SVN using the web URL. But how can a monorepo help solve all of them? 20 Entertaining Uses of ChatGPT You Never Knew Were Possible Ben "The Hosk" Hosking in ITNEXT The Difference Between The Clever Developer & The Wise Developer Alexander Nguyen in Level Up Coding $150,000 Amazon Engineer vs. $300,000 Google Engineer fatfish in JavaScript in Plain English Its 2022, Please Dont Just Use console.log As a matter-of-fact, it would not wrong to say that that the individuals at Google, Facebook, and Twitter must have had some strong reasons to turn to Monorepos instead of going with thousands of smaller repositories. This is because Bazel is not used for driving the build in this case, in Costs and trade-offs. Such reorganization would necessitate cultural and workflow changes for Google's developers. Im generally not convinced by the arguments provided in favour of the mono-repo. Protecting all the information in your Google Account has never been more important. In Proceedings of the 10th Joint Meeting on Foundations of Software Engineering (Bergamo, Italy, Aug. 30-Sept. 4). As a comparison, Google's Git-hosted Android codebase is divided into more than 800 separate repositories. The visualization is interactive meaning you are able to search, filter, hide, focus/highlight & query the nodes in the graph. Coincidentally, I came across two interesting articles from Google Research around this topic: With an introduction to the Google scale (9 billion source files, 35 million commits, 86TB Those are all good things, so why should teams do anything differently? To reduce the incidence of bad code being committed in the first place, the highly customizable Google "presubmit" infrastructure provides automated testing and analysis of changes before they are added to the codebase. Tools for building and splitting monolithic repository from existing packages. No need to worry about incompatibilities because of projects depending on conflicting versions of third party libraries. Oao. Piper supports file-level access control lists. Rachel starts by discussing a previous job where she was working in the gaming industry. Wikipedia. (2 minutes) Competition for Google has long been just a click away. Most of this has focused on how the monorepo impacts Google developer productivity and Single Repository, Communications of the ACM, July 2016, Vol. CitC supports code browsing and normal Unix tools with no need to clone or sync state locally. With the monolithic structure of the Google repository, a developer never has to decide where the repository boundaries lie. The clearest example of this are the game engines, which Please The Google code-browsing tool CodeSearch supports simple edits using CitC workspaces. It then uses the index to construct a reachability graph and determine what classes are never used. I would however argue that many of the stated benefits of the mono-repo above are simply not limited to mono repos and would work perfectly fine in a much more natural multiple repos. This effort is in collaboration with the open source Mercurial community, including contributors from other companies that value the monolithic source model. Flag flips make it much easier and faster to switch users off new implementations that have problems. I would challenge the fact that having owners is not in the best interest of shared ownership, so Im not a fan. though, it became part of our companys monolithic source repository, which is shared 9. We also review the advantages and trade-offs of this model of source code management. Looking at Facebooks Mercurial The design and architecture of these systems were both heavily influenced by the trunk-based development paradigm employed at Google, as described here. Developer tools may be as important as the type of repo. The code for sgeb can be found in build/cicd/sgeb. However, it is also necessary that tooling scale to the size of the repository. We definitely have code colocation, but if there are no well defined relationships among them, we would not call it a monorepo. Then, without leaving the code browser, they can send their changes out to the appropriate reviewers with auto-commit enabled. Rachel will go into some details about that. Bazel has been refined and tested for years at Google to build heavy-duty, mission-critical infrastructure, services, and applications. More importantly, I wanted to better understand the benefits and But there are other extremely important things such as dev ergonomics, maturity, documentation, editor support, etc. In the open source world, dependencies are commonly broken by library updates, and finding library versions that all work together can be a challenge. It is best suited to organizations like Google, with an open and collaborative culture. Work fast with our official CLI. If it's a normal Bazel target (like a Go program), sgeb will delegate to Bazel. The availability of all source code in a single repository, or at least on a centralized server, makes it easier for the maintainers of core libraries to perform testing and performance benchmarking for high-impact changes before they are committed. As the scale and If you don't like the SLA (including backwards compatibility), you are free to compile your own binary package to run in production. When the review is marked as complete, the tests will run; if they pass, the code will be committed to the repository without further human intervention. We are open sourcing - Made with love by Nrwl (the company behind Nx). requirements for our infrastructure: Windows based: game developers, especially non-programmers, heavily rely on windows based tooling, The Git community strongly suggests and prefers developers have more and smaller repositories. On the same machine, you will never build or test the same thing twice. This article outlines the scale of Googles codebase, describes Googles custom-built monolithic source repository, and discusses the reasons behind choosing this model. ACM Press, New York, 2015, 191201. Monorepos can reach colossal sizes. You can check on And it's common that each repo has a single build artifact, and simple build pipeline. Because this autonomy is provided by isolation, and isolation harms collaboration. The industry has moved to the polyrepo way of doing things for one big reason: team autonomy. Developers must be able to explore the codebase, find relevant libraries, and see how to use them and who wrote them. order to simplify distribution. In the game engine examples, there would be an unreal_builder that d. Over 99% of files stored in Piper are visible to all full-time Google engineers. Google uses cookies to deliver its services, to personalize ads, and to analyze traffic. Josh Levenberg (joshl@google.com) is a software engineer at Google, Mountain View, CA. The goal was to maintain as much logic as possible within the monorepo Builders can be found in build/builders. Trunk-based development is beneficial in part because it avoids the painful merges that often occur when it is time to reconcile long-lived branches. Build, or sgeb. Developers can instead store Piper workspaces on their local machines. ], 4.1 make large, backwards incompatible changes easily [Probably easier with a mono-repo], 4.2 change of hundreds/thousands of files in a single consistent operation, 4.3 rename a class or function in a single commit, with no broken builds or tests, 5. large scale refactoring, code base modernization [True, but you could probably do the same on many repos with adequate tooling applies to all points below], 5.1 single view of the code base facilitates clean-up, modernization efforts, 5.1.1 can be centrally managed by dedicated specialists, 5.1.2 e.g. At Google, theyve had a mono-repo since forever, and I recall they were using Perforce but they have now invested heavily in scalability of their mono-repo. 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