Everything you need to know about monorepos, and the tools to build them. Determine what might be affected by a change, to run only build/test affected projects. infrastructure may be a bottleneck when verifying new change sets (e.g., too slow, too (2 minutes) Competition for Google has long been just a click away. Im generally not convinced by the arguments provided in favour of the mono-repo. 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 targets themselves, meaning that can be written in any language that sgeb supports. Figure 2 reports the number of unique human committers per week to the main repository, January 2010-July 2015. It is best suited to organizations like Google, with an open and collaborative culture. The Google code-browsing tool CodeSearch supports simple edits using CitC workspaces. The monolithic codebase captures all dependency information. Thanks to our partners for supporting us! WebThere are many great monorepo tools, built by great teams, with different philosophies. Teams want to make their own decisions about what libraries they'll use, when they'll deploy their apps or libraries, and who can contribute to or use their code. Working state is thus available to other tools, including the cloud-based build system, the automated test infrastructure, and the code browsing, editing, and review tools. We also review the advantages and trade-offs of this model of source code management. Meanwhile, the number of Google software developers has steadily increased, and the size of the Google codebase has grown exponentially (see Figure 1). fit_screen Simply Some features are easy to add even when a given tool doesn't support it (e.g., code generation), and some aren't really possible to add (e.g., distributed task execution). If nothing happens, download GitHub Desktop and try again. A developer can make a major change touching hundreds or thousands of files across the repository in a single consistent operation. Advantages. Essentially, I was asking the question does it scale? let's see how each tools answer to each features. About monorepo.tools . Google repository statistics, January 2015. amount of work to get it up and running again. CRA, Babel, Jest are a few projects that use it. Includes only reviewed and committed code and excludes commits performed by automated systems, as well as commits to release branches, data files, generated files, open source files imported into the repository, and other non-source-code files. No effort goes toward writing or keeping documentation up to date, but developers sometimes read more than the API code and end up relying on underlying implementation details. Here is a curated list of articles about monorepos that we think will greatly support what you just learned. submodule-based multi-repo model, I was curious about the rationale of choosing the If you don't like the SLA (including backwards compatibility), you are free to compile your own binary package to run in production. IEEE Micro 30, 4 (2010), 6579. But you're not alone in this journey. order to simplify distribution. Instead of creating separate repositories for new projects, they A monorepo is a single version-controlled repository that contains several isolated projects with well-defined relationships. WebGoogle's monolithic repository provides a common source of truth for tens of thousands of developers around the world. In 2014, approximately 15 million lines of code were changedb in approximately 250,000 files in the Google repository on a weekly basis. This behavior can create a maintenance burden for teams that then have trouble deprecating features they never meant to expose to users. Conference on Software Engineering: Software Engineering in Practice, pp. Still the big picture view of all services and support code is very valuable even for small teams. If a change creates widespread build breakage, a system is in place to automatically undo the change. Samsung extended its self-repair program to include the Galaxy Book Pro 15" and the Galaxy Book Pro 360 15" shown above. Bigtable: A distributed storage system for structured data. work. In that vein, we determined the following The monorepo changes the way you interact with other teams such that everything is always integrated. This file can be found in build_protos.bat. There is a tension between having all dependencies at the latest version and having versioned dependencies. The ability to store and replay file and process output of tasks. Many people know that Google uses a single repository, the monorepo, to store all internal source code. Not until recently did I ask the question to myself. 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! If you thought the term Monstrous Monorepo is a little over sensational, let me tell you some facts about the Google Monorepo. Things like support for distributed task execution can be a game changer, especially in large monorepos. This is because it is a polyglot (multi-language) build system designed to work on monorepos: It encourages further revisions and a conversation leading to a final "Looks Good To Me" from the reviewer, indicating the review is complete. There is effectively a SLA between the team that publish the binary and the clients that uses them. While Bazel is very extensible and supports many targets, there are certain projects that it is not [2] You can see more documentation on this on docs/sgeb.md. Figure 1. A lot of successful organizations such as Google, Facebook, Microsoft -as well as large open source projects such as Babel, Jest, and React- are all using the monorepo approach to software development. drives the Unreal build and an unity_builder that drives the Unity builds. Despite the effort required, Google repeatedly chose to stick with the central repository due to its advantages. A snapshot of the workspace can be shared with other developers for review. The total number of files also includes source files copied into release branches, files that are deleted at the latest revision, configuration files, documentation, and supporting data files; see the table here for a summary of Google's repository statistics from January 2015. Let's define what we and others typically mean when we talk about Monorepos. Tools for building and splitting monolithic repository from existing packages. We do not intend to support or develop it any further. 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. In addition, lost productivity ensues when abandoned projects that remain in the repository continue to be updated and maintained. Rachel Potvin (rpotvin@google.com) is an engineering manager at Google, Mountain View, CA. see in each individual package or code where the code is expected to be but overall they conform to The clearest example of this are the game engines, which Wasserman, L. Scalable, example-based refactorings with Refaster. Google's monolithic software repository, which is used by 95% of its software developers worldwide, meets the definition of an ultra-large-scale4 system, providing evidence the single-source repository model can be scaled successfully. Credit: Iwona Usakiewicz / Andrij Borys Associates. Visualize dependency relationships between projects and/or tasks. Piper also has limited interoperability with Git. Each and every directory has a set of owners who control whether a change to files in their directory will be accepted. Because this autonomy is provided by isolation, and isolation harms collaboration. Work fast with our official CLI. setup, the toolchains, the vendored dependencies are not present. ), Rachel then mentions that developers work in their own workspaces (I would assume this a local copy of the files, a Perforce lingo.). We definitely have code colocation, but if there are no well defined relationships among them, we would not call it a monorepo. Tools have been built to. Tricorder also provides suggested fixes with one-click code editing for many errors. caveats. ACM Transactions on Computer Systems 31, 3 (Aug. 2013). What are the situations solved by monorepos. No need to worry about incompatibilities because of projects depending on conflicting versions of third party libraries. Some would argue this model, which relies on the extreme scalability of the Google build system, makes it too easy to add dependencies and reduces the incentive for software developers to produce stable and well-thought-out APIs. Corbett, J.C., Dean, J., Epstein, M., Fikes, A., Frost, C., Furman, J., Ghemawat, S., Gubarev, A., Heiser, C., Hochschild, P. et al. would have to be re-vendored as needed). However, as the scale increases, code discovery can become more difficult, as standard tools like grep bog down. This article outlines the scale of Googles codebase, describes Googles custom-built monolithic source repository, and discusses the reasons behind choosing this model. An important aspect of Google culture that encourages code quality is the expectation that all code is reviewed before being committed to the repository. Google chose the monolithic-source-management strategy in 1999 when the existing Google codebase was migrated from CVS to Perforce. Copyright 2023 by the ACM. The combination of trunk-based development with a central repository defines the monolithic codebase model. Several best practices and supporting systems are required to avoid constant breakage in the trunk-based development model, where thousands of engineers commit thousands of changes to the repository on a daily basis. 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. cases Bazel should be used. This approach has served Google well for more than 16 years, and today the vast majority of Google's software assets continues to be stored in a single, shared repository. The line for total commits includes data for both the interactive use case, or human users, and automated use cases. 7, Pages 78-87 sgeb will then build and invoke this builder for them. Most of this traffic originates from Google's distributed build-and-test systems.c. Overview. In most cases it is now impossible to build 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. WebSearch the world's information, including webpages, images, videos and more. In October 2012, Google's central repository added support for Windows and Mac users (until then it was Linux-only), and the existing Windows and Mac repository was merged with the main repository. Each day the repository serves billions of file read requests, with approximately 800,000 queries per second during peak traffic and an average of approximately 500,000 queries per second each workday. By adding consistency, lowering the friction in creating new projects and performing large scale refactorings, by facilitating code sharing and cross-team collaboration, it'll allow your organization to work more efficiently. development environments, which can be asked with one simple question: Teams that use open source software are expected to occasionally spend time upgrading their codebase to work with newer versions of open source libraries when library upgrades are performed. we welcome pull requests if we got something wrong! we vendored. We added a simple script to and branching is exceedingly rare (more yey!!). Rachel Potvin and Josh Levenberg, Why Google Stores Billions of Lines of Code in a 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. Most of this has focused on how the monorepo impacts Google developer productivity and Jennifer Lopez wore the iconic Versace dress at the 2000 Grammy Awards. Copyright2016 ACM, Inc. Chang, F., Dean, J., Ghemawat, S., Hsieh, W.C., Wallach, D.A., Burrows, M., Chandra, T., Fikes, A., and Gruber, R.E. Most important, it supports: The second article is a survey-based case study where hundreds Google engineers were asked This article outlines the scale of Googles codebase, 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. Code visibility and clear tree structure providing implicit team namespacing. In fact, such a repo is prohibitively monolithic, which is often the first thing that comes to mind when people think of monorepos. If it's a normal Bazel target (like a Go program), sgeb will delegate to Bazel. NOTE: This is not a working system as it is published here. sample code search, API auto-update, pre-commit CI verify jobs with impact analysis and The effect of this merge is also apparent in Figure 1. It's complex, we know. These builders are sgeb Release branches are cut from a specific revision of the repository. In Proceedings of the IEEE International Conference on Software Maintenance (Eindhoven, The Netherlands, Sept. 22-28). 7. Click The visualization is interactive meaning you are able to search, filter, hide, focus/highlight & query the nodes in the graph. Google White Paper, 2011; http://info.perforce.com/rs/perforce/images/GoogleWhitePaper-StillAllonOneServer-PerforceatScale.pdf. The code for the cicd code can be found in build/cicd. While the tooling builds, The Google codebase includes approximately one billion files and has a history of approximately 35 million commits spanning Google's entire 18-year existence. This will require you to install the protoc compiler. We do our best to represent each tool objectively, and we welcome pull Here, we provide background on the systems and workflows that make feasible managing and working productively with such a large repository. In 2011, Google started relying on the concept of API visibility, setting the default visibility of new APIs to "private." Trunk-based development. More complex codebase modernization efforts (such as updating it to C++11 or rolling out performance optimizations9) are often managed centrally by dedicated codebase maintainers. Repository, and isolation harms collaboration a SLA between the team that the... Monolithic repository provides a common source of truth for tens of thousands of files across repository. 'S information, including webpages, images, videos and more code discovery can become more,! They never meant to expose to users also review the advantages and trade-offs this... 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Monorepo, to run only build/test affected projects, 6579 human committers week., built by great teams, with different philosophies Potvin ( rpotvin @ google.com ) is an Engineering at...