Git/Gerrit evaluation

This is the homepage for the Gerrit review taskforce created at the 2012 Berlin Hackathon.

Timeline

 * July - build this page out with all serious alternatives
 * July - wikitech-l discussion about alternatives.
 * Week of August 6 - final review discussion

Brion Vibber will lead this evaluation, with help from Chad Horohoe and David Schoonover.

Reference Materials

 * Our Gerrit, in all its glory.
 * List of Gerrit Bugs That Matter
 * In order to properly understand Gerrit, you might want to try performing a few common tasks (please do add more here):
 * Attempt to find a link to the source for a project

Criteria by which to judge a code review tool
We need criteria by which to judge the validity of arguments in favor / opposed to Gerrit. It seems to me that these criteria should be derived by the workflow(s) that we want to support. Obviously, the platform team and Ops wants to have a pre-commit review workflow. But looking at other teams, there seem to be other workflows in place as well. For example, the Mobile and Analytics Teams have post-commit review workflows. Ideally, a code review tool should allow different kinds of workflows.

Criteria
(please add / removeas you see fit, this is condensend opinion from the Analytics Team)


 * Support for pre-commit and post-commit review workflows (Unopinionated / does not impose a particular workflow)
 * Easy and clear diffs between commits
 * It has to be beautiful and moddable
 * It should make source code easy discoverable
 * Support for pull requests

The case for Gerrit

 * Primary editor: Chad Horohoe. Others should feel free to contribute.


 * LDAP integration. LDAP is a requirement for tie-ins with Labs and other developer/operations projects. Gerrit supports this out of the box with minimal configuration.
 * Robust ACL. Gerrit has the ability to grant/deny permissions on the repository level and even down to the branch level. This is important because different teams have different workflows for their branches.
 * Additionally, Labs requires a private repository for puppet.
 * Automatic merge on approve, unlike Phabricator that only works with patches (which then must be applied to the repository).
 * Open source, under active development. Using free and open source software is very important to our community, and Gerrit is licensed under the Apache License. Additionally, the Gerrit project has a very active development community that is highly responsive to feedback, questions, and contributions. Google develops Gerrit to support the Android Open Source Project (AOSP), but there are many other contributors, including Qt and OpenStack.
 * Quick release cycle. 2.2.x, 2.3.x and 2.4.x have all been released in the last year (with 2.3 and 2.4 both in the last several months). 2.5 is in active development currently.
 * Handles 'pre-commit' style review. One of the major motivations for switching from Subversion was for the ability to review changes before they landed in trunk/master. This has stabilized our codebase and enabled the rolling release cycle to WMF wikis (currently every 2 weeks, working towards every week).
 * Command line access. It's possible to interface with Gerrit from the command line, which makes scripting Gerrit actions relatively easy, and provides a less hideous alternative to the Gerrit UI.
 * SSH handled by gerrit From a security perspective, it's nice that Gerrit doesn't use the system SSH, which means users don't have shell access to the gerrit host, and we don't need hacks like sillyshell.

Known issues slated for improvement

 * Slowness due to the current deployment configuration -- should be fixable by moving the database closer to app server (currently in different datacenters, sorry!)
 * Ease of extending Gerrit -- in 2.5, Gerrit is adding a plugin/extension interface that should make it easier for us to add MediaWiki/WMF-specific features we want or need (in fact, "Project Deletion" is already being written as a plugin!)

The case against Gerrit

 * Primary editor: David Schoonover. Others should feel free to contribute.


 * Gerrit accounts must be requested. This slows down all contributions, and is particularly egregious in that it slows down onboarding of new WMF staff. Weeks have been lost waiting for all necessary rights to be given to new staff.
 * Is this an inherent issue or is that something we can reasonably change? What limitations exactly prevent us from allowing open registration? --brion (talk) 17:47, 11 July 2012 (UTC)
 * Gerrit does not have an official API. Existing tools work by reverse-engineering Gerrit's internal APIs, which are largely undocumented.
 * It is not possible to alter the sort order in which changes are listed. Changes are listed by last update date, so the changes that have been neglected the longest are also the hardest to see. A feature request for parametrizing the sort order was accepted in 2010, but no progress has been made as of July 2012..
 * Gerrit's developers want to move away from using a relational database as a data store. As a result, they are reluctant to invest time in improving Gerrit's query interface. Such a change would entail a costly migration for us.
 * Gerrit's codebase is written in Java and Prolog(!) and uses Google Web Toolkit. Few (if any) engineers at the foundation are proficient with this stack. Large swaths of code in the Gerrit codebase are undocumented, making it hard to understand or modify.
 * I dont see this as a problem necessarily unless we expect to modify the codebase. As for Prolog and Java, I have coded in both languages (it has been a while using Prolog, but it is fairly easy to pick up if ever this became necessary).  Ssastry (talk) 15:58, 11 July 2012 (UTC)
 * I disagree, its a very very minor point to be sure, but things are better when most people can read/edit the code, since its easier to fix issues when they arise, and customize to our needs. (I also know prolog, and like that language, but it is an obscure language). Bawolff (talk) 19:48, 11 July 2012 (UTC)
 * The ability to add a repository requires administrator privileges on Gerrit. However, administrator privileges also grant unlimited access to gsql, a raw SQL interface to the Gerrit database. As a result, administrator rights cannot be extended beyond a narrow group of people (currently five). This creates a frustrating bottleneck for developers, who must compete for the attention of the overburdened administrator group for routine Git requests.
 * Gerrit is slow.  The "Groups" listing takes almost a minute to render.
 * There is no way to delete projects. A request for this feature was opened in 2009 and has been starred by over a hundred people.
 * As of 19:59, 10 July 2012 (UTC) There are 164 issues on the Gerrit bug tracker that are status:accepted and have no owner. Of those, two are set as "critical" and twelve are set as "major".
 * I don't neccesarily see that as a bad thing. Have you seen our bug database? Better they track issues that they don't have resources to or otherwise aren't working on now, then to just simply sweep them under the rug. Bawolff (talk) 19:48, 11 July 2012 (UTC)
 * Post-merge review is impossible. Comments just get lost and bugs are not effective.
 * Lost how? Do they not save, or are there error messages? What do you mean "bugs are not effective"? --brion (talk) 17:49, 11 July 2012 (UTC)
 * It is difficult find or track projects unless someone walks you through it. For example, there is only one very small, hidden link to view the list of projects. This makes the state of any particular branch pretty opaque and potentially creates an issue for managers or others who want to have a window into our code.
 * There is little to no ability for non-technical staff or volunteers to meaningfully contribute (e.g. to processes like code review or simply commenting). Compare to GitHub or even Bugzilla, where FOSS projects see a large amount of comments or other contributions from designers, product managers, or users whether they have familiarity with git or commit access.
 * Can you articulate more clearly what the issue is here? Anyone with an account can comment or even -1/+1 commits. And we have a very large and complex codebase (MediaWiki + extensions + ops stuff + tools and misc), no matter where we host it, which of course makes it harder for people to jump in and comment. Does GitHub offer specific tools that would help engage non-technical folks, or are you just saying "Gerrit's UI sucks" one more time?.--Eloquence (talk) 17:41, 11 July 2012 (UTC)
 * I suspect the main problem comes down to 'accounts must be requested' up above -- you can't make comments until you've been placed in the system, whereas github, bugzilla etc allow open registration. --brion (talk) 17:46, 11 July 2012 (UTC)
 * UI sucks profoundly: too wide, clumsy, no visual comparison for image changes (ol' good CodeReview did this!), no "view this file" link, just "download as zip" (WTF????).
 * Operaphobic
 * Per the UI sucks, It's not desinged to encurage volenteer development, its geered towards a single project, single team proccess for deployable code. Look at the main "landing page" ... there is little concept of what projects are represented, no per project pages with descriptions, no agragate views of which projects are more active than others, no person icons, no sense who is working on what, too focused on individual commits rather then the final change state represented by a pull request for a particualr feature or refactor. There is a false sense of linear pipeline rather than a distributed collection of interconected activity. There is no big "fork me" button! ( there is no per-project interface views, so not clear where you would put that ). Aside from getting deployable code the tools for feature develop should also encurage expeirmentations and be fun. Github is good at doing this, makes coding and sharing "fun". Gerrit is not fun.  --Mdale (talk) 23:28, 11 July 2012 (UTC)
 * Sometimes, development requires a number of commits before a feature/bug/change/refactoring can be fully worked out. So, code review requires a review of a set of commits rather than individual commits.  I may not be fully aware of Gerrit's abilities, but a commit-based review model gets in the way of such review flows.  Alternatively, it prevents developers from committing something and amending commits till all work on that phase is complete.  This may also encourage work in smaller reviewable chunks, so, I am not going to make this a strong case against gerrit.  I prefer frequent and regular commits to let others work on it or take over partially done work -- and the in-progress commits may not necessarily be reviewable or need to be reviewed.  Ssastry (talk) 03:32, 12 July 2012 (UTC)

Integrated options
Integrated option means it manages the repositories as well as the review process.


 * Github
 * Gitorious
 * Gitlabs
 * Gerrit

The case for Github

 * Anyone can participate in development -- creating user accounts, forking, commenting, submitting issues, etc. are all easy and open to anyone and removes WMF from the loop as far as these areas are concerned.
 * Commit rights determine who gets to push code to the repo.

Deploy and development repositories:
 * Maintain 2 repositories: one "deploy" repository that has very few admins, and another "development" repository that has a lot more trusted developers.
 * Code gets into the deploy repository only via pull requests from the development repository -- this can only be done when "trusted" developers/admins do necessary code reviews and issue pull requests to the deploy repository.
 * Periodic downstream rebasing/merging from the deploy repo into the development repo, if necessary (to account for any direct commits into the deploy repo).

To ensure bad code does not get into the deploy repository, development repository might have to be managed as follows:
 * Topic branches are used for code that requires review.
 * Commits on the master branch that are not reviewed, and cannot be part of a pull request are moved to a branch.
 * Problematic commits into the development repo either get fixed or reverted.
 * Protocols required for who can issue pull requests into the deploy repository.

Code gets into the development repository in 2 ways:
 * trusted developers (staff, volunteers, aliens) get commit rights and can directly push code.
 * anyone else in the world (who dont have commit access to the development repo) forks the development repo and issues a pull request into the development repo.
 * pull requests are used to do code review.

Reviewing development repo commits:
 * Via github comments -- drawback is that there is no way to track reviews. Given current review requirements via Gerrit, unlikely to be an acceptable model.
 * Via an external standalone review tool like barkeep.

Drawbacks:
 * Depending on review requirements, could require a standalone review tool like barkeep to track reviews.
 * Reviews are not enforced, unlike Gerrit.
 * Depends on developers acting trustworthily and following protocols.

Standalone code review tools
These tools profess to do the job of code review completely independently of repository management
 * Phabricator
 * Barkeep
 * Review Board

Standalone repo management tools
These tools don't provide code review, but only provide access control for the repository.
 * Gitosis
 * Gitolite

Git repo viewers

 * gitweb (default with Git and Gerrit)
 * cgit