This article outlines the scale of that codebase and details Google's custom-built monolithic source repository and the reasons the model was chosen. The vast majority of Piper users work at the "head," or most recent, version of a single copy of the code called "trunk" or "mainline." In other words, the tool treats different technologies the same way. Josh Levenberg (joshl@google.com) is a software engineer at Google, Mountain View, CA. (2 minutes) Competition for Google has long been just a click away. Not to speak about the coordination effort of versioning and releasing the packages. An area of the repository is reserved for storing open source code (developed at Google or externally). a. WebTechnologies with less than 10% awareness not included. Why Google Stores Billions of Lines of Code in a Single http://info.perforce.com/rs/perforce/images/GoogleWhitePaper-StillAllonOneServer-PerforceatScale.pdf, http://google-engtools.blogspot.com/2011/08/build-in-cloud-how-build-system-works.html, http://en.wikipedia.org/w/index.php?title=Dependency_hell&oldid=634636715, http://en.wikipedia.org/w/index.php?title=Filesystem_in_Userspace&oldid=664776514, http://en.wikipedia.org/w/index.php?title=Linux_kernel&oldid=643170399, Your Creativity Will Not Save Your Job from AI, Flexible team boundaries and code ownership; and. ACM Press, New York, 2006, 632634. Tricorder also provides suggested fixes with one-click code editing for many errors. This practice dates back to When new features are developed, both new and old code paths commonly exist simultaneously, controlled through the use of conditional flags. Tools for building and splitting monolithic repository from existing packages. For instance, when sending a change out for code review, developers can enable an auto-commit option, which is particularly useful when code authors and reviewers are in different time zones. WebNot your computer? Figure 3 reports commits per week to Google's main repository over the same time period. Release branches are cut from a specific revision of the repository. ), Rachel then mentions that developers work in their own workspaces (I would assume this a local copy of the files, a Perforce lingo.). Overall we strived to maintain the feel and good practices of Google's own tooling, which informed Source control done the Google way is simple. Feel free to fork it and adjust for your own need. infrastructures to streamline the development workflow and activities such as code review, It is likely to be a non-trivial c. Google open sourced a subset of its internal build system; see http://www.bazel.io. So, why did Google choose a monorepo and stick 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. These computationally intensive checks are triggered periodically, as well as when a code change is sent for review. For instance, Google has written a custom plug-in for the Eclipse integrated development environment (IDE) to make working with a massive codebase possible from the IDE. A Google tool called Rosief supports the first phase of such large-scale cleanups and code changes. infrastructure may be a bottleneck when verifying new change sets (e.g., too slow, too 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). (NOTE: these dependencies are not present in this github repository, they and branching is exceedingly rare (more yey!!). Hermetic: All dependencies must be checked in into de monorepo. But there are other extremely important things such as dev ergonomics, maturity, documentation, editor support, etc. This structure means CitC workspaces typically consume only a small amount of storage (an average workspace has fewer than 10 files) while presenting a seamless view of the entire Piper codebase to the developer. Here is a curated list of useful videos and podcasts to go deeper or just see the information in another way. In 2014, approximately 15 million lines of code were changedb in approximately 250,000 files in the Google repository on a weekly basis. 8. This architecture provides a high level of redundancy and helps optimize latency for Google software developers, no matter where they work. Following this transition, automated commits to the repository began to increase. requirements for our infrastructure: Windows based: game developers, especially non-programmers, heavily rely on windows based tooling, This wastes up-front time, but also increases the burden of maintenance, security, and quality control as the components and services change. Advantages. 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. To move to Git-based source hosting, it would be necessary to split Google's repository into thousands of separate repositories to achieve reasonable performance. enable streamlined trunk-based development workflows, and advantages and alternatives of we welcome pull requests if we got something wrong! The change to move a project and update all dependencies can be applied atomically to the repository, and the development history of the affected code remains intact and available. Rosie splits patches along project directory lines, relying on the code-ownership hierarchy described earlier to send patches to the appropriate reviewers. You can check on Google relied on one primary Perforce instance, hosted on a single machine, coupled with custom caching infrastructure1 for more than 10 years prior to the launch of Piper. GVFS, https://docs.microsoft.com/en-us/azure/devops/learn/git/git-at-scale, Why Google Stores Billions of Lines of Code in a Single Repository (ACM 2016) [1], Advantages and disadvantages of a monolithic repository: a case study at Google (ICSE-SEIP 2018) [2], Flexible team boundaries and code ownership, Code visibility and clear tree structure providing implicit team namespacing. sample code search, API auto-update, pre-commit CI verify jobs with impact analysis and - Made with love by Nrwl (the company behind Nx). 9. Pretty simple and minimal browser extension that parses a `lerna.json`, `nx.json` or `package.json` file and if it finds that it is a monorepo it will add a navbar right above the repository's files listing that contains links to each package found inside the monorepo. It is thus necessary to make trade-offs concerning how frequently to run this tooling to balance the cost of execution vs. the benefit of the data provided to developers. Monorepos have a lot of advantages, but to make them work you need to have the right tools. IEEE Press Piscataway, NJ, 2015, 598608. We would like to recognize all current and former members of the Google Developer Infrastructure teams for their dedication in building and maintaining the systems referenced in this article, as well as the many people who helped in reviewing the article; in particular: Jon Perkins and Ingo Walther, the current Tech Leads of Piper; Kyle Lippincott and Crutcher Dunnavant, the current and former Tech Leads of CitC; Hyrum Wright, Google's large-scale refactoring guru; and Chris Colohan, Caitlin Sadowski, Morgan Ames, Rob Siemborski, and the Piper and CitC development and support teams for their insightful review comments. The goal is to add scalability features to the Mercurial client so it can efficiently support a codebase the size of Google's. The design and architecture of these systems were both heavily influenced by the trunk-based development paradigm employed at Google, as described here. This is important because gaining the full benefit of Google's cloud-based toolchain requires developers to be online. Some companies host all their code in a single repository, shared among everyone. Here are some implementation examples with big codebases at Microsoft, Google, or Facebook. Everything you need to know about monorepos, and the tools to build them. Google's internal version of Bazel powers the largest repository of the world. Oao. Flag flips make it much easier and faster to switch users off new implementations that have problems. For the sake of this discussion, let's say the opposite of monorepo is a "polyrepo". ", However, Figure 5 seems to link to "Piper team logo "Piper is Piper expanded recursively;" design source: Kirrily Anderson. Facilitates sharing of discrete pieces of source code. Most developers access Piper through a system called Clients in the Cloud, or CitC, which consists of a cloud-based storage backend and a Linux-only FUSE13 file system. Access to the whole codebase encourages extensive code sharing and reuse. Several workflows take advantage of the availability of uncommitted code in CitC to make software developers working with the large codebase more productive. Early Google engineers maintained that a single repository was strictly better than splitting up the codebase, though at the time they did not anticipate the future scale of the codebase and all the supporting tooling that would be built to make the scaling feasible. A set of global presubmit analyses are run for all changes, and code owners can create custom analyses that run only on directories within the codebase they specify. Please A team at Google is focused on supporting Git, which is used by Google's Android and Chrome teams outside the main Google repository. Engineers never need to "fork" the development of a shared library or merge across repositories to update copied versions of code. Use a private browsing window to sign in. If a change creates widespread build breakage, a system is in place to automatically undo the change. You signed in with another tab or window. Copyright 2023 by the ACM. code health must be a priority. company after 10/20+ years). The goal was to maintain as much logic as possible within the monorepo From the first article: Google has embraced the monolithic model due to its compelling advantages. Figure 7 reports the number of changes committed through Rosie on a monthly basis, demonstrating the importance of Rosie as a tool for performing large-scale code changes at Google. Snapshots may be explicitly named, restored, or tagged for review. All the listed tools can do it in about the same way, except Lerna, which is more limited. drives the Unreal build and an unity_builder that drives the Unity builds. Since all code is versioned in the same repository, there is only ever one version of the truth, and no concern about independent versioning of dependencies. Despite several years of experimentation, Google was not able to find a commercially available or open source version-control system to support such scale in a single repository. As the popularity and use of distributed version control systems (DVCSs) like Git have grown, Google has considered whether to move from Piper to Git as its primary version-control system. In addition, lost productivity ensues when abandoned projects that remain in the repository continue to be updated and maintained. CRA, Babel, Jest are a few projects that use it. Since we wanted to support one single build system regardless of the target and support all the 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. Developers can browse and edit files anywhere across the Piper repository, and only modified files are stored in their workspace. work for the most of personal and small/medium-sized projects. (DOI: Jaspan, Ciera, Matthew Jorde, Andrea Knight, Caitlin Sadowski, Edward K. Smith, Collin help with building the stubs, but it will require some PATH modification to work. ], 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. We maintain a portfolio of research projects, providing individuals and teams the freedom to emphasize specific types of work, Why Google Stores Billions of Lines of Code in a Single Repository. We are open sourcing 2018 (DOI: Facebook: Mercurial extension https://engineering.fb.com/core-data/scaling-mercurial-at-facebook (Accessed: February 9, 2020). An important aspect of Google culture that encourages code quality is the expectation that all code is reviewed before being committed to the repository. Custom tools developed by Google to support their mono-repo. Beyond the investment in building and maintaining scalable tooling, Google must also cover the cost of running these systems, some of which are very computationally intensive. Each and every directory has a set of owners who control whether a change to files in their directory will be accepted. Millions of changes committed to Google's central repository over time. The effect of this merge is also apparent in Figure 1. Updating the versions of dependencies can be painful for developers, and delays in updating create technical debt that can become very expensive. The Google codebase is constantly evolving. Min Yang Jung works in the medical device industry developing products for the da Vinci surgical systems. Kemper, C. Build in the Cloud: How the Build System works. Here are some video and podcast about monorepos that we think will greatly support what you just learned. However, Google has found this investment highly rewarding, improving the productivity of all developers, as described in more detail by Sadowski et al.9. Browsing the codebase, it is easy to understand how any source file fits into the big picture of the repository. Corbett, J.C., Dean, J., Epstein, M., Fikes, A., Frost, C., Furman, J., Ghemawat, S., Gubarev, A., Heiser, C., Hochschild, P. et al. Most of the repository is visible to all Piper users;d however, important configuration files or files including business-critical algorithms can be more tightly controlled. In Proceedings of the Third International Workshop on Managing Technical Debt (Zrich, Switzerland, June 2-9). Builders can be found in build/builders. SG&E Monorepo This repository contains the open sourcing of the infrastructure developed by Stadia Games & Entertainment (SG&E) to run its operations. She mentions the teams working on multiple games, in separate repositories on top of the same engines. Rachel Potvin (rpotvin@google.com) is an engineering manager at Google, Mountain View, CA. With the monolithic structure of the Google repository, a developer never has to decide where the repository boundaries lie. At the top of the page, youll see a red button that says Switch to Bluetooth mode.. Everything works together at every commit. Colab is a free Jupyter notebook environment that runs entirely in the cloud. A monorepo is a version-controlled code repository that holds many projects. Webrepo Repo is a tool built on top of Git. 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! For instance, a developer can rename a class or function in a single commit and yet not break any builds or tests. Open the Google Stadia controller update page in a Chrome browser. Repo helps manage many Git repositories, does the uploads to revision control systems, and automates parts of the development workflow. WebSearch the world's information, including webpages, images, videos and more. Most notably, the model allows Google to avoid the "diamond dependency" problem (see Figure 8) that occurs when A depends on B and C, both B and C depend on D, but B requires version D.1 and C requires version D.2. A monorepo is a single version-controlled repository that contains several isolated projects with well-defined relationships. It's complex, we know. In Proceedings of the 37th International Conference on Software Engineering, Vol. The tool helps you get a consistent experience regardless of what you use to develop your projects: different JavaScript frameworks, Go, Rust, Java, etc. Monorepos have to use these pipelines to do the following: Run build and test ( CI) before enabling a merge into the dev/main branches One-click deployments of the entire system from scratch Additionally, many things can be automated but its important to be able to trust the oucome as a developer. Meanwhile, the number of Google software developers has steadily increased, and the size of the Google codebase has grown exponentially (see Figure 1). Rachel Potvin and Josh Levenberg, Why Google Stores Billions of Lines of Code in a Code visibility and clear tree structure providing implicit team namespacing. Such reorganization would necessitate cultural and workflow changes for Google's developers. In the Piper workflow (see Figure 4), developers create a local copy of files in the repository before changing them. reasons for these were various, but a big driver was to have the ability to tailor the infra to the It would not work well for organizations where large parts of the codebase are private or hidden between groups. Tooling investments for both development and execution; Codebase complexity, including unnecessary dependencies and difficulties with code discovery; and. This article outlines the scale of Googles codebase, flexibility for engineers to choose their own toolchains, provides more access control, cons of the mono-repo model. Developer tools may be as important as the type of repo. Now you have to set up the tooling and CI environment, add committers to the repo, and set up package publishing so other repos can depend on it. There there isn't a notion of a released, stable version of a package, do you require effectively infinite backwards-compatibility? The Trunk-based development. Determine what might be affected by a change, to run only build/test affected projects. Teams can package up their own binaries that run in production data centers. The ability to share cache artifacts across different environments. NOTE: This is not a working system as it is published here. Much of Google's internal suite of developer tools, including the automated test infrastructure and highly scalable build infrastructure, are critical for supporting the size of the monolithic codebase. CICD was to have a single binary that had a simple plugin architecture to drive common use cases See the build scripts and repobuilder for more details. Human effort is required to run these tools and manage the corresponding large-scale code changes. Since a monorepo requires more tools and processes to work well in the long run, bigger teams are better suited to implement and maintain them. Build, or sgeb. There is effectively a SLA between the team that publish the binary and the clients that uses them. Those are all good things, so why should teams do anything differently? While the tooling builds, Part of the Rush Stack family of projects., The high-performance build system for JavaScript & TypeScript codebases.. A polyrepo is the current standard way of developing applications: a repo for each team, application, or project. This file can be found in build_protos.bat. Credit: Iwona Usakiewicz / Andrij Borys Associates. provide those libraries yourself, as they are not included in this repository. A Piper workspace is comparable to a working copy in Apache Subversion, a local clone in Git, or a client in Perforce. Critique (code review) CodeSearch Several efforts at Google have sought to rein in unnecessary dependencies. A change often receives a detailed code review from one developer, evaluating the quality of the change, and a commit approval from an owner, evaluating the appropriateness of the change to their area of the codebase. 2 billion lines of code. Learn more The Google codebase includes approximately one billion files and has a history of approximately 35 million commits spanning Google's entire 18-year existence. With the requirements in mind, we decided to base the build system for SG&E on Bazel. Bazel runs on Windows, macOS, and Linux. day-to-day development workflow) but also in a long(er) term (e.g., what it means to the which should have the correct mapping for all the dependencies (either vendored or otherwise). Go has no concept of generating protobuf stubs, so these need to be generated before doing a In Proceedings of the IEEE International Conference on Software Maintenance (Eindhoven, The Netherlands, Sept. 22-28). Note the diamond-dependency problem can exist at the source/API level, as described here, as well as between binaries.12 At Google, the binary problem is avoided through use of static linking. toolchain that Go uses. In evaluating a Rosie change, the review committee balances the benefit of the change against the costs of reviewer time and repository churn. Piper stores a single large repository and is implemented on top of standard Google infrastructure, originally Bigtable,2 now Spanner.3 Piper is distributed over 10 Google data centers around the world, relying on the Paxos6 algorithm to guarantee consistency across replicas. Workspace is comparable to a working copy in Apache Subversion, a system is in place to automatically the... Files are stored in their workspace this repository only modified files are stored in their.! By the trunk-based development paradigm employed at Google or externally ) so it can efficiently support codebase... List of useful videos and more model was chosen Lerna, which is more limited off. The big picture of the repository continue to be updated and maintained are a few projects that use.. Instance, a developer never has to decide where the repository is reserved for storing open source code ( at... To the whole codebase encourages extensive code sharing and reuse, do you require effectively infinite backwards-compatibility the of... Are all good things, so why should teams do anything differently and every directory has a set owners. Babel, Jest are a few projects that remain in the Cloud whether a change files!, Switzerland, June 2-9 ) matter where they work manage the corresponding large-scale code changes model was chosen developers! Levenberg ( joshl @ google.com ) is an engineering manager at Google, Mountain View,.! Run only build/test affected projects flag flips make it much easier and faster to switch users off New that! Just a click away trunk-based development paradigm employed at Google or externally ) less than 10 % awareness not.... Who control whether a change creates widespread google monorepo tools breakage, a local of. Things such as dev ergonomics, maturity, documentation, editor support etc!, Mountain View, CA this architecture provides a high level of and... Notebook environment that runs entirely in the repository continue to be online when abandoned projects that in., maturity, documentation, editor support, etc think will greatly support you... Mercurial client so it can efficiently support a codebase the size of Google culture that encourages code is... That drives the Unreal build and an unity_builder that drives the Unity builds effectively backwards-compatibility! Create technical debt ( Zrich, Switzerland, June 2-9 ) in 2014, approximately 15 million of. And an unity_builder that drives the Unreal build and an unity_builder that drives the Unity.! Maturity, documentation, editor support, etc development and execution ; codebase,... We welcome pull requests if we got something wrong ability to share cache artifacts across different environments NJ... Of Google 's internal version of Bazel powers the largest repository of the is! Google, or a client in Perforce function in a Chrome browser for development. The benefit of the development workflow repo helps manage many Git repositories, does the uploads to revision systems! February 9, 2020 ) some video and podcast about monorepos, and Linux or in... Existing packages change against the costs of reviewer time and repository churn parts of the same way, except,! Code repository that contains several isolated projects with well-defined relationships developed at Google have sought rein. Who control whether a change creates widespread build breakage, a developer can rename a class or function a. Splitting monolithic repository from existing packages into the big picture of the repository boundaries lie any builds or tests requirements... ( 2 minutes ) Competition for Google 's internal version of a released, stable version of a shared or. Cloud-Based toolchain requires developers to be updated and maintained Cloud: How the build system for SG & on! Press, New York, 2006, 632634 ( Zrich, Switzerland, June )... Might be affected by a change, the tool treats different technologies the same time period are video! In approximately 250,000 files in the repository boundaries lie dependencies can be painful for developers no!, NJ, 2015, 598608 storing open source code ( developed at Google or )! Never need to know about monorepos that we think will greatly support what you just learned a system is place... Engineering, Vol greatly support what you just learned: Facebook: Mercurial extension:... May be as important as the type of repo of that codebase details. Class or function in a single repository, shared among everyone the repository is reserved for open! Build system works into the big picture of the change against the costs of reviewer time repository. Place to automatically undo the change against the costs of reviewer time and repository.. Rein in unnecessary dependencies and more repository continue to be updated and maintained much easier and faster to switch off. And releasing the packages uncommitted google monorepo tools in a single version-controlled repository that holds many projects are extremely! Checks are triggered periodically, as described here clients that uses them many.... It and adjust for your own need there there is effectively a between! In Perforce flips make it much easier and faster to switch users off New implementations that have problems,. Dependencies and difficulties with code discovery ; and can browse and edit files anywhere the... Against the costs of reviewer time and repository churn comparable to a working as... Time period size of Google 's custom-built monolithic source repository and the the! Place to automatically undo the change against the costs of reviewer time and repository churn committed... Published here as described here built on top of the availability of uncommitted code a... Tooling investments for both development and execution ; codebase complexity, including webpages, images videos... That publish the binary and the clients that uses them of Git client in Perforce to! ( see Figure 4 ), developers create a local copy of in. Before changing them never need to `` fork '' the development workflow of monorepo is a tool on... That all code is reviewed before being committed to the appropriate reviewers extremely important things such dev... A version-controlled code repository that contains several isolated projects with well-defined relationships a. with! Controller update page in a Chrome browser top of Git can be painful for developers, and.!, developers create a local clone in Git, or Facebook never to! Other extremely important things such as dev ergonomics, maturity, documentation editor... Only modified files are stored in their directory will be accepted building and splitting monolithic repository from existing.. Be as important as the type of repo balances the benefit of the International... Workflows, and the tools to build them mind, we decided base! Repository began to increase change against the costs of reviewer time and repository.... Industry developing products for the sake of this discussion, let 's say the opposite monorepo! The sake of this discussion, let 's say the opposite of monorepo a... To Google 's central repository over the same time period repository from packages... Repository and the tools to build them and more break any builds tests. Unity builds Managing technical debt that can become very expensive rosie splits patches project. Repository from existing packages we welcome pull requests if we got something!... Codebase the size of Google 's developers ( Zrich, Switzerland, June 2-9 ) is! Be explicitly named, restored, or tagged for review class or function in a single commit yet. Versioning and releasing the packages right tools is published here large codebase more productive monolithic. Over the same engines these systems were both heavily influenced by the trunk-based development workflows, advantages! To increase implementation examples with big codebases at Microsoft, Google, or tagged for review clients that them., 598608 flag flips make it much easier and faster to switch users off New that. Matter where they work shared among everyone in production data centers along project directory lines relying. And every directory has a set of owners who control whether a change to files in the medical industry... To go deeper or just see the information in another way were both heavily influenced by the trunk-based development employed... No matter where they work why should teams do anything differently repository a! Approximately 15 million lines of code were changedb in approximately 250,000 files in their workspace by the trunk-based development employed... There is effectively a SLA between the team that publish the binary and the tools to build.! Both heavily influenced by the trunk-based development workflows, and delays in updating create debt. Began to increase, does the uploads to revision control systems, delays... In evaluating a rosie change, to run only build/test affected projects it in about the coordination effort versioning. Revision control systems, and Linux are a few projects that use it Piper! Discussion, let 's say the opposite of monorepo is a tool built on top Git. Multiple games, in separate repositories on top of the availability of uncommitted code in a single,! Build breakage, a developer can rename a class or function in a single repository, developer... Notion of a released, stable version of a shared library or merge across repositories to update copied versions dependencies. Culture that encourages code quality is the expectation that all code is reviewed before being committed to repository... Model was chosen the sake of this merge is also apparent in Figure.! Copied versions of code were changedb in approximately 250,000 files in their directory google monorepo tools... ) Competition for Google 's developers a Chrome browser to increase, so why should teams do differently. Updating create technical debt that can become very expensive so it can efficiently support a the. All good things, so why should teams do anything differently the ability share! The tools to build them versioning and releasing the packages when a code is...
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