The combination of trunk-based development with a central repository defines the monolithic codebase model. repository: a case study at Google, In Proceedings of the 40th International Developers can confidently contribute to other teams applications and verify that their changes are safe. The use of Git is important for these teams due to external partner and open source collaborations. As the scale and In Proceedings of the IEEE International Conference on Software Maintenance (Eindhoven, The Netherlands, Sept. 22-28). a monorepo, so we decided to have all of our code and assets in one single repository. The industry has moved to the polyrepo way of doing things for one big reason: team autonomy. Build, or sgeb. NOTE: This is not a working system as it is published here. And hey, our industry has a name for that: continuous normal Go toolchain (eg. Take up to $50 off the Galaxy S23 series by reserving your phone right now. This means that your whole organisation, including CI agents, will never build or test the same thing twice. In other words, the tool treats different technologies the same way. basis in different areas. WebTechnologies with less than 10% awareness not included. Our strategy for adopted the mono-repo model but with different approaches/solutions, Perf results on scaling Git on VSTS with normal build. This entails part of the build system setup, the CICD Owners are typically the developers who work on the projects in the directories in question. From the first article: Google has embraced the monolithic model due to its compelling advantages. drives the Unreal build and an unity_builder that drives the Unity builds. Updates from the Piper repository can be pulled into a workspace and merged with ongoing work, as desired (see Figure 5). This article outlines the scale of Googles codebase, describes Googles custom-built monolithic source repository, and discusses the reasons behind choosing this model. SG&E was running on a custom environment that was different from normal Google operations. 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. Rosie then takes care of splitting the large patch into smaller patches, testing them independently, sending them out for code review, and committing them automatically once they pass tests and a code review. There is effectively a SLA between the team that publish the binary and the clients that uses them. WebThere are many great monorepo tools, built by great teams, with different philosophies. 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. Curious to hear your thoughts, thanks! Team boundaries are fluid. uncommon target, programmers are able to write custom programs that know how to build that target. Work fast with our official CLI. A Git-clone operation requires copying all content to one's local machine, a procedure incompatible with a large repository. It is important to note that the way the project builds in this github repository is not the same Trunk-based development. Google workflow. Robert. 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. Google, Meta, Microsoft, Uber, Airbnb, and Twitter are some of the well-known companies to run large monorepos. 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. Most of the infrastructure was written in Go, using protobuf for configuration. 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. The fact that Piper users work on a single consistent view of the Google codebase is key for providing the advantages described later in this article. The ability to run tasks in the correct order and in parallel. company after 10/20+ years). On the same machine, you will never build or test the same thing twice. Custom tools developed by Google to support their mono-repo. 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. - 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? 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. As you will see in this book, a monorepo approach can save developers from a great deal of headache and wasted time. Sec. This file can be found in build_protos.bat. Another attribute of a monolithic repository is the layout of the codebase is easily understood, as it is organized in a single tree. All this content has been created, reviewed and validated by these awesome folks. She mentions the mono-repo is a giant tree, where each directory has a set of owners who must approve the change. Source control done the Google way is simple. Developers see their workspaces as directories in the file system, including their changes overlaid on top of the full Piper repository. blog.google Uninterrupted listening across devices with Android At CES 2023, well share new experiences for bringing media with you across devices and our approach to helping devices work better together. Piper and CitC make working productively with a single, monolithic source repository possible at the scale of the Google codebase. Spanner: Google's globally distributed database. 5. 10. 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. b. In that vein, we determined the following Let's define what we and others typically mean when we talk about Monorepos. Some companies host all their code in a single repository, shared among everyone. This behavior can create a maintenance burden for teams that then have trouble deprecating features they never meant to expose to users. Most of this traffic originates from Google's distributed build-and-test systems.c. Piper can also be used without CitC. In the open source world, dependencies are commonly broken by library updates, and finding library versions that all work together can be a challenge. IEEE Press Piscataway, NJ, 2015, 598608. It is now read-only. 2 billion lines of code. Dependency-refactoring and cleanup tools are helpful, but, ideally, code owners should be able to prevent unwanted dependencies from being created in the first place. Find quick answers, explore your interests, and stay up to date with Discover. The internal tools developed by Google to support their monorepo are impressive, and so are the stats about the number of files, commits, and so forth. As the scale and complexity of projects both inside and outside Google continue to grow, we hope the analysis and workflow described in this article can benefit others weighing decisions on the long-term structure for their codebases. Browsing the codebase, it is easy to understand how any source file fits into the big picture of the repository. We created this resource to help developers understand what monorepos are, what benefitsthey can bring, and the tools available to make monorepo development delightful. Rachel Potvin and Josh Levenberg, Why Google Stores Billions of Lines of Code in a 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. Figure 5. Open source of the build infrastructure used by Stadia Games & Entertainment. would have to be re-vendored as needed). There is a tension between consistent style and tool use with freedom and flexibility of the toolchain. Google's tooling for repository merges attributes all historical changes being merged to their original authors, hence the corresponding bump in the graph in Figure 2. There are many great monorepo tools, built by great teams, with different philosophies. Linux kernel. Credit: Iwona Usakiewicz / Andrij Borys Associates. In fact, such a repo is prohibitively monolithic, which is often the first thing that comes to mind when people think of monorepos. How Google manages open source. 9 million unique source files. 4. So, why did Google choose a monorepo and stick Bloch, D. Still All on One Server: Perforce at Scale. and independently develop each sub-project while the main project moves forward (I will An important aspect of Google culture that encourages code quality is the expectation that all code is reviewed before being committed to the repository. Which developer tools is more worth it between monorepo.tools and Solo Learn. This practice dates back to updating the codebase to make use of C++11 features, 5.2 monolithic codebase captures all dependency information, 5.2.1 old APIs can be removed with confidence, 6. collaboration across teams [Not related to mono-repos, but to permissioning policies], 7. flexible team boundaries and code ownership [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], 8. code visibility and clear tree structure providing implicit team namespacing [True, but you could probably do the same on many repos with adequate tooling and BitBucket or GitHub are providing some of the required features], 3.1 find and remove unused/underused dependencies and dead code, 3.2 support large scale clean-ups and refactoring. 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. found in build/cicd/cirunner. But you're not alone in this journey. 8. Instead of creating separate repositories for new projects, they 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. we welcome pull requests if we got something wrong! of content, ~40k commits/workday as of 2015), the first article describes why Google chose for contribution purposes mostly. Monorepos can reach colossal sizes. For example, due to this centralized effort, Google's Java developers all saw their garbage collection (GC) CPU consumption decrease by more than 50% and their GC pause time decrease by 10%40% from 2014 to 2015. Flag flips make it much easier and faster to switch users off new implementations that have problems. 2. And it's common that each repo has a single build artifact, and simple build pipeline. cons of the mono-repo model. - 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? sample code search, API auto-update, pre-commit CI verify jobs with impact analysis and Turborepo is the monorepo for Vercel, the leading platform for frontend frameworks. 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. NOTE: This open source version was modified to build with the normal Go flow (go build), with some Migration is usually done in a three step process: announce, new code and move over, then deprecate old code by deletion. provide those libraries yourself, as they are not included in this repository. Total size of uncompressed content, excluding release branches. 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. These costs and trade-offs fall into three categories: In many ways the monolithic repository yields simpler tooling since there is only one system of reference for tools working with source. The effect of this merge is also apparent in Figure 1. build internally as a black box. 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. If one team wants to depend on another team's code, it can depend on it directly. Managing this scale of repository and activity on it has been an ongoing challenge for Google. 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. Because this autonomy is provided by isolation, and isolation harms collaboration. Builders are meant to build targets that Additionally, this is not a direct benefit of the mono-repo, as segregating the code into many repos with different owners would lead to the same result. There was a problem preparing your codespace, please try again. Current investment by the Google source team focuses primarily on the ongoing reliability, scalability, and security of the in-house source systems. There are a number of potential advantages but at the highest level: 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. f. The project name was inspired by Rosie the robot maid from the TV series "The Jetsons.". assessment, and so forth. Jan. 17, 2023 1:06 p.m. PT. But if it is a more 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. Alternatives Website Twitter. This system is not being worked on anymore, so it will not have any support. Tooling investments for both development and execution; Codebase complexity, including unnecessary dependencies and difficulties with code discovery; and. Reducing cognitive load is important, but there are many ways to achieve this. Each tool fits a specific set of needs and gives you a precise set of features. You may find, say, Lage more enjoyable to use than Nx or Bazel even though in some ways it is less capable. The visualization is interactive meaning you are able to search, filter, hide, focus/highlight & query the nodes in the graph. A snapshot of the workspace can be shared with other developers for review. [2] Filesystem in userspace. d. 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