Learn more. You can check on The Google build system5 makes it easy to include code across directories, simplifying dependency management. If you don't like the SLA (including backwards compatibility), you are free to compile your own binary package to run in production. This wastes up-front time, but also increases the burden of maintenance, security, and quality control as the components and services change. We also review the advantages and trade-offs of this model of source code management. 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. The monolithic model makes it easier to understand the structure of the codebase, as there is no crossing of repository boundaries between dependencies. We do our best to represent each tool objectively, and we welcome pull requests if we got something wrong! The monorepo changes the way you interact with other teams such that everything is always integrated. 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). infrastructure may be a bottleneck when verifying new change sets (e.g., too slow, too Before reviewing the advantages and disadvantages of working with a monolithic repository, some background on Google's tooling and workflows is needed. In evaluating a Rosie change, the review committee balances the benefit of the change against the costs of reviewer time and repository churn. Credit: Iwona Usakiewicz / Andrij Borys Associates. 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. The ability to execute any command on multiple machines while developing locally. A tag already exists with the provided branch name. Those are all good things, so why should teams do anything differently? 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. possible targets, we decided to create a layer on top of Bazel that would cover all the cases: SG&E One concrete example is an experiment to evaluate the feasibility of converting Google data centers to support non-x86 machine architectures. Each and every directory has a set of owners who control whether a change to files in their directory will be accepted. These files are stored in a workspace owned by the developer. Browsing the codebase, it is easy to understand how any source file fits into the big picture of the repository. 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. cons of the mono-repo model. 'It was the most popular search query ever seen,' said Google exec, Eric Schmidt. The effect of this merge is also apparent in Figure 1. There was a problem preparing your codespace, please try again. - 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? In 2011, Google started relying on the concept of API visibility, setting the default visibility of new APIs to "private." Updating the versions of dependencies can be painful for developers, and delays in updating create technical debt that can become very expensive. These computationally intensive checks are triggered periodically, as well as when a code change is sent for review. We at Nrwl think this is the most consistent and accurate statement of what a monorepo is among all the established monorepo tools. Each source file can be uniquely identified by a single stringa file path that optionally includes a revision number. Googles Rachel Potvin made a presentation during the @scale conference titled Why Google Stores Billions of Lines of Code in a Single Repository. This file can be found in build_protos.bat. Use Git or checkout with SVN using the web URL. Supports definition of rules to constrain dependency relationships within the repo. 3. Current investment by the Google source team focuses primarily on the ongoing reliability, scalability, and security of the in-house source systems. 9 million unique source files. But it will analyze Cargo.toml files to do the same for Rust, or Gradle files to do the same for Java. The five key findings from the article are as follows (from Team boundaries are fluid. Oao isnt the most mature, rich, or easily usable tool on the list, but its Google's monolithic repository provides a common source of truth for tens of thousands of developers around the world. 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. In practice, Everything you need to know about monorepos, and the tools to build them. Since Google's source code is one of the company's most important assets, security features are a key consideration in Piper's design. You can 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. A Git-clone operation requires copying all content to one's local machine, a procedure incompatible with a large repository. Everything works together at every commit. Tooling exists to help identify and remove unused dependencies, or dependencies linked into the product binary for historical or accidental reasons, that are not needed. Tools for Monorepo. Things like support for distributed task execution can be a game changer, especially in large monorepos. Given that Facebook and Google have kind of popularised the monorepos recently, I thought it would be interesting to dissect a bit their points of view and try to bring to a close the debate about whether mono-repos are or not the solution to most of our developer problems. Updating is difficult when the library callers are hosted in different repositories. ACM Press, New York, 2006, 632634. Keep reading, and you'll see that a good monorepo is the opposite of monolithic. All rights reserved. In Proceedings of the 37th International Conference on Software Engineering, Vol. a. IEEE Press Piscataway, NJ, 2012, 16. You can see more documentation on this on docs/sgeb.md. Most of the infrastructure was written in Go, using protobuf for configuration. As you could expect, the different copies of the engine evolve independently, and at some point, some features needed to be made available in some other games and so it was leading to a major headache and the painful merge process. 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. ], 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. WebYour Google Account gives you a safe, central place to store your personal information like credit cards, passwords, and contacts so its always available for you across the internet when you need it. Copyright 2023 by the ACM. A developer can make a major change touching hundreds or thousands of files across the repository in a single consistent operation. A Piper workspace is comparable to a working copy in Apache Subversion, a local clone in Git, or a client in Perforce. How Google manages open source. build internally as a black box. Josh Levenberg (joshl@google.com) is a software engineer at Google, Mountain View, CA. Inconsistency creates mental overhead of remembering which commands to use from project to project. This article outlines the scale of Googles codebase, For the current project, Files in a workspace are committed to the central repository only after going through the Google code-review process, as described later. The ability to share cache artifacts across different environments. other setups (eg. Here is a curated list of useful videos and podcasts to go deeper or just see the information in another way. Visualize dependency relationships between projects and/or tasks. We are open sourcing WebGoogle uses the single monorepo for 95% of its single source of truth codebase, leaving Google Chrome and Android on specific ones. And hey, our industry has a name for that: continuous 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. You wil need to compile and Google has many special features to help you find exactly what you're looking for. This article outlines the scale of that codebase and details Google's custom-built monolithic source repository and the reasons the model was chosen. Advantages. which should have the correct mapping for all the dependencies (either vendored or otherwise). We do our best to represent each tool objectively, and we welcome pull requests if we got Another attribute of a monolithic repository is the layout of the codebase is easily understood, as it is organized in a single tree. While these projects may be related, they are often logically independent and run by different teams. A monorepo changes your organization & the way you think about code. 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. Bazel has been refined and tested for years at Google to build heavy-duty, mission-critical infrastructure, services, and applications. system and a number of tools developed for internal use, some experimental in nature, some saw more 5. Developers must be able to explore the codebase, find relevant libraries, and see how to use them and who wrote them. Advantages of Monorepo. Accessed Jan. 20, 2015; http://en.wikipedia.org/w/index.php?title=Linux_kernel&oldid=643170399. (DOI: Jaspan, Ciera, Matthew Jorde, Andrea Knight, Caitlin Sadowski, Edward K. Smith, Collin The Google codebase is constantly evolving. Chang, F., Dean, J., Ghemawat, S., Hsieh, W.C., Wallach, D.A., Burrows, M., Chandra, T., Fikes, A., and Gruber, R.E. Storing all in-progress work in the cloud is an important element of the Google workflow process. For the last project that I worked You can give it a fancy name like "garganturepo," but we're sorry to say, it's not a monorepo. Tooling also exists to identify underutilized dependencies, or dependencies on large libraries that are mostly unneeded, as candidates for refactoring.7 One such tool, Clipper, relies on a custom Java compiler to generate an accurate cross-reference index. In that vein, we determined the following Spanner: Google's globally distributed database. Section "Background", paragraph five, states: "Updates from the Piper repository can be pulled into a workspace and merged with ongoing work, as desired (see Figure 5). This heavily decreases the 15. Here is a curated list of books about monorepos that we think are worth a read. We provide background on the systems and workflows that make managing and working productively with a large repository feasible. Such reorganization would necessitate cultural and workflow changes for Google's developers. Google still has a Git infrastructure team mostly for open source projects : https://www.youtube.com/watch?v=cY34mr71ky8, Link to the research papers written by Rachel and Josh on Why Google Stores Billions of Lines of Code in a Single Repository, Why Google Stores Billions of Lines of Code in a Single Repository, https://www.youtube.com/watch?v=cY34mr71ky8, http://research.google.com/pubs/pub45424.html, http://dl.acm.org/citation.cfm?id=2854146, Piper (custom system hosting monolithic repo), TAP (testing before and after commits, auto-rollback), Rosie (large scale change distribution and management), codebase complexity is a risk to productivity. Figure 2 reports the number of unique human committers per week to the main repository, January 2010-July 2015. We created this resource to help developers understand what monorepos are, what benefitsthey can bring, and the tools available to make monorepo development delightful. be installed into third_party/p4api. ), Google does trunk based development (Yey!!) The Digital Library is published by the Association for Computing Machinery. Piper and CitC make working productively with a single, monolithic source repository possible at the scale of the Google codebase. This would provide Google's developers with an alternative of using popular DVCS-style workflows in conjunction with the central repository. MONOREPO). These systems provide important data to increase the effectiveness of code reviews and keep the Google codebase healthy. This entails part of the build system setup, the CICD As the scale and Android Police. we vendored. In the game engine examples, there would be an unreal_builder that Rachel Potvin (rpotvin@google.com) is an engineering manager at Google, Mountain View, CA. The risk associated with developers changing code they are not deeply familiar with is mitigated through the code-review process and the concept of code ownership. Lerna is probably the grand daddy of all monorepo tools. Several efforts at Google have sought to rein in unnecessary dependencies. Depending on your needs and constraints, we'll help you decide which tools best suit you. Trunk-based development. An important aspect of Google culture that encourages code quality is the expectation that all code is reviewed before being committed to the repository. Piper can also be used without CitC. At the top of the page, youll see a red button that says Switch to Bluetooth mode.. 8. 59 No. A monorepo is a version-controlled code repository that holds many projects. Click This is because Bazel is not used for driving the build in this case, in Morgenthaler, J.D., Gridnev, M., Sauciuc, R., and Bhansali, S. Searching for build debt: Experiences managing technical debt at Google. This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository. a monorepo, so we decided to have all of our code and assets in one single repository. https://cacm.acm.org/magazines/2016/7/204032-why-google-stores- Sec. This requires the tool to be pluggable. Essentially, I was asking the question does it scale? However, Google has found this investment highly rewarding, improving the productivity of all developers, as described in more detail by Sadowski et al.9. As you will see in this book, a monorepo approach can save developers from a great deal of headache and wasted time. As the last section showed, some third party code and libraries would be needed to build. Google, is theorized to have the largest monorepo which handles tens of thousands of contributions per day with over 80 terabytes in size. If nothing happens, download GitHub Desktop and try again. It then uses the index to construct a reachability graph and determine what classes are never used. Robert. This system is not being worked on anymore, so it will not have any support. 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. Rachel will go into some details about that. Kemper, C. Build in the Cloud: How the Build System works. SG&E was running on a custom environment that was different from normal Google operations. Single Repository, Communications of the ACM, July 2016, Vol. The ability to understand the project graph of the workspace without extra configuration.