This document contains various instructions relevant for Druid committers.

PR and issue action item checklist for committers

This checklist describes steps that every committer should take for their own issues and PRs and when they are the first committer who visits an issue or a PR authored by a non-committer.

1. Add appropriate tags to the PR, in particular:

   • Design Review - for changes that will be hard to undo after they appear in some Druid release, and/or changes that will have lasting consequences in the codebase. Examples:

     • Major architectural changes or API changes
     • Adding new or changing behaviour of existing query types (e. g. changing an algorithm behind some query type or changing from floating point to double precision)
     • Adding new or changing existing HTTP requests and responses (e. g. a new HTTP endpoint)
     • Adding new or changing existing interfaces for extensions (@PublicApi and @ExtensionPoint)
     • Adding new or changing existing server configuration parameter (e. g. altering the behavior of a config parameter)
     • Adding new or changing existing emitted metrics
     • Other major changes

     PRs that flesh out community standards, checklists, policies, and PRs that change issue and PR templates, in other words, many of the PRs tagged Area - Dev should often be tagged Design Review as well.

     The PR description should succinctly, but completely list all public API elements (@PublicApi or @ExtensionPoint), configuration options, emitted metric names, HTTP endpoint paths and parameters that are added or changed in the PR. If they are not listed, ask the PR author to update the PR description.

   • Incompatible - for changes that alter public API elements (@PublicApi or @ExtensionPoint), runtime configuration options, emitted metric names, HTTP endpoint behavior, or server behavior in some way that affects one of the following:

     • Ability to do a rolling update as documented without needing any modifications to server configurations or query workload.
     • Ability to roll back a Druid cluster to a prior version.
     • Ability to continue using old Druid extensions without recompiling them.

     Note that no matter what, we must support the ability to do a rolling update somehow (even if some special care is needed), and the ability to roll back to at least the immediate prior Druid version. If a change makes either one of these impossible then it should be re-designed.

     All Incompatible PRs should be tagged Design Review too, but not vice versa: some Design Review issues, proposals and PRs may not be Incompatible.

   • Release Notes - for important changes that should be reflected in the next Druid’s version release notes. Critically, those are changes that require some server or query configuration changes made by Druid cluster operators to preserve the former cluster behaviour, i. e. the majority of PRs tagged Incompatible. However, some Incompatible PRs may not need to be tagged Release Notes, e. g. PRs that only change some extension APIs, because when building extensions with the newer Druid version the incompatibility will be discovered anyway.

     Secondarily, PRs that add new features, improve performance or improve Druid cluster operation experience could also be tagged Release Notes at your discretion.

   • Bug / Security / Feature / Performance / Refactoring / Improvement - can be used to distinguish between types of changes. Compatibility tag also falls into this category, it's specifically for PRs that restore or improve compatibility with previous Druid versions if it was inadvertently broken, or for changes that ensure forward compatibility with future Druid versions, forseening specific changes that would otherwise break the compatibility.

   • Development Blocker - for changes that need to be merged before some other PRs could even be published. Development Blocker PRs should be prioritized by reviewers, so that they could be merged as soon as possible, thus not blocking somebody's work.

2. Consider adding one or several Area - tags to the PR or issue. Consider creating a new Area - tag if none of the existing Area tags is applicable to the PR or issue.

   • Area - Automation/Static Analysis - for any PRs and issues about Checkstyle, forbidden-apis, IntelliJ inspections, code style, etc. Should also be used for PRs and issue related to TeamCity CI problems.
   • Area - Cache - for PRs and issues related to Druid‘s query results cache (local or remote). Don’t use for PRs that anyhow relate to caching in different contexts.
   • Area - Dev - for PRs and issues related to the project itself, such as adding developer‘s docs and checklists, Github issue and PR templates, Github-related issues. Don’t use for PRs and issues related to CI problems: use either Area - Testing for problems with Travis or Area - Automation/Static Analysis for problems with TeamCity. PRs with Area - Dev tag should usually change files in dev/ or .github/ directories.
   • Area - Documentation - for PRs and issues about Druid‘s documentation for users and cluster operators. Don’t use for PRs and issues about the documentation of the Druid‘s development process itself: use Area - Dev for that purpose. Don’t use for issues and PR regarding adding internal design documentation and specification to code, usually, in the form of Javadocs or comments (there is no specialized tag for this).
   • Area - Lookups - for PRs and issues related to Druid's Query Time Lookups (QTL) feature.
   • Area - Null Handling - for PRs and issues related to the Null Handling project.
   • Area - Operations - for PRs and issues related to Druid cluster operation process, for example, PRs adding more alerting, logging, changing configuration options.
   • Area - Query UI - for issues that mention or discuss the questions related to presenting Druid query results for human perception.
   • Area - Querying - for any PRs and issues related to the process of making data queries against Druid clusters, including the PRs and issues about query processing and aggregators.
   • Area - Segment Balancing/Coordination - for PRs and issue related to the process of loading and dropping segments in Druid clusters according to specified rules, and balancing segments between Historical nodes in clusters. Coordinator node is responsible for both processes. This tag is not called “Area - Coordinator” because Coordinator has some other duties that are not covered by this tag, for example, compacting segments.
   • Area - Testing - use for any PRs and issues related to testing (including integration testing), Travis CI issues, and flaky tests. For flaky tests, also add Flaky test tag.
   • Area - Zookeeper/Curator - for any PRs and issues related to ZooKeeper, Curator, and node discovery in Druid.

3. Consider adding any Bug and Security PRs to the next Druid milestone whenever they are important enough to fix before the next release. This ensures that they will be considered by the next release manager as potential release blockers. Please don‘t add PRs that are neither Bug nor Security-related to milestones until after they are committed, to avoid cluttering the release manager’s workflow.

4. If the PR has obvious problems, such as an empty description or the PR fails the CI, ask the PR author to fix these problems even if you don't plan to review the PR.

5. If you create an issue that is relatively small and self-contained and you don't plan to work on it in the near future, consider tagging it Contributions Welcome so that other people know that the issue is free to pick up and is relatively easily doable even for those who are not very familiar with the codebase.

PR merge action item checklist

1. Add the PR to the next release milestone.

2. If the PR is labeled Incompatible and the next release milestone differs from the previous only in the “patch” number (such as 0.10.1, while the previous release is 0.10 or 0.10.0), rename the next milestone so that it bumps the “minor” number (e. g. 0.10 -> 0.11).

3. Check that the issue addessed in the PR is closed automatically by Github. If it's not, close the issue manually.

4. Consider thanking the author for contribution, especially a new contributor.

Creating a new tag on Github

After creating a tag for your PR or issue, don't forget to take the following steps:

1. Search existing PRs and issues and try to add the new tag to at least three of them.

2. Describe the new tag in the PR and issue action item checklist for committers above.

3. Although it is not necessary to preliminarily discuss creation of a new tag in the developers' mailing list, please announce the new tag after you've created it at dev@druid.apache.org.

Become an Administrator of the Druid project in TeamCity

Druid committers shall obtain a status of a Druid project administrator. See the corresponding section in the document about TeamCity for details.