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How to Contribute to Apache Hive

This page describes the mechanics of how to contribute software to Apache Hive. For ideas about what you might contribute, please see open tickets in Jira.

Getting the Source Code

First of all, you need the Hive source code. As of April 2015 Hive has moved to git for its repository.

Get the source code on your local drive using git. See Understanding Hive Branches below to understand which branch you should be using.

git clone https://git-wip-us.apache.org/repos/asf/hive.git

Setting Up Eclipse Development Environment (Optional)

This is an optional step. Eclipse has a lot of advanced features for Java development, and it makes the life much easier for Hive developers as well.

How do I import into eclipse?

Becoming a Contributor

This checklist tells you how to create accounts and obtain permissions needed by Hive contributors.  See the Hive website for additional information.

  • Create an Apache Software Foundation JIRA account if you do not already have one:  Sign Up for JIRA.
    • The ASF JIRA system dashboard is here.
    • The Hive JIRA is here. 
  • To review patches for JIRA tickets, use the Review Board.  If you need an account, register here.  See Review Process below for more information.
    • All Hive patches posted for review are listed here.
    • Individual JIRA tickets provide a link to the issue on the review board when a review request has been made.
    • For simple reviews, you can just read the patch attached to the JIRA ticket and post a comment.
  • To contribute to the Hive wiki, follow the instructions in About This Wiki.
  • To edit the Hive website, follow the instructions in How to edit the website.
  • Join the Hive mailing lists to receive email about issues and discussions.

Making Changes

Before you start, send a message to the Hive developer mailing list, or file a bug report in JIRA. Describe your proposed changes and check that they fit in with what others are doing and have planned for the project. Be patient, it may take folks a while to understand your requirements.

Modify the source code and add some features using your favorite IDE.

Coding Conventions

Please take care about the following points.

  • All public classes and methods should have informative Javadoc comments.
    • Do not use @author tags.
  • Code should be formatted according to Sun's conventions, with two exceptions:
    • Indent two (2) spaces per level, not four (4).
    • Line length limit is 100 chars, instead of 80 chars.
  • Contributions should not introduce new Checkstyle violations.
    • Check for new Checkstyle violations by running mvn checkstyle:checkstyle-aggregate, and then inspect the results in the target/site directory.
    • If you use Eclipse you should install the eclipse-cs Checkstyle plugin. This plugin highlights violations in your code and is also able to automatically correct some types of violations.
  • Contributions should pass existing unit tests.
  • New unit tests should be provided to demonstrate bugs and fixes. JUnit is our test framework:
    • You must implement a class that extends junit.framework.TestCase and whose class name starts with Test.
    • Define methods within your class whose names begin with test, and call JUnit's many assert methods to verify conditions; these methods will be executed when you run mvn test.
    • You can run all the unit tests with the command mvn test -Phadoop-1, or you can run a specific unit test with the command mvn test -Phadoop-1 -Dtest=<class name without package prefix> (for example:  mvn test -Phadoop-1 -Dtest=TestFileSystem).

Understanding Maven

Hive is a multi-module Maven project. If you are new to Maven, the articles below may be of interest:

Additionally, Hive actually has two projects, "core" and "itests". The reason that itests is not connected to the core reactor is that itests requires the packages to be built.

The actual Maven commands you will need are discussed on the HiveDeveloperFAQ page.

Understanding Hive Branches

As of June 2015, Hive has two "main lines", master and branch-1.  

All new feature work and bug fixes in Hive are contributed to the master branch. As of June 2015, releases from master are numbered 2.x.  2.x versions are not necessarily backwards compatible with 1.x versions.

branch-1 is used to build stable, backward compatible releases. Releases from this branch are numbered 1.x (where 1.3 will be the first release from it, as 1.2 was released from master prior to the creation of branch-1). Until at least June 2016 all critical bug fixes (crashes, wrong results, security issues) applied to master must also be applied to branch-1. The decision to port a feature from master to branch-1 is at the discretion of the contributor and committer. However no features that break backwards compatibility will be accepted on branch-1.

In addition to these main lines Hive has two types of branches, release branches and feature branches.

Release branches are made from branch-1 (for 1.x) or master (for 2.x) when the community is preparing a Hive release. Release branches match the number of the release (e.g., branch-1.2 for Hive 1.2). For patch releases the branch is made from the existing release branch (to avoid picking up new features from the main line). For example, if a 1.2.1 release was being made branch-1.2.1 would be made from the tip of branch-1.2. Once a release branch has been made, inclusion of additional patches on that branch is at the discretion of the release manager. After a release has been made from a branch, additional bug fixes can still be applied to that branch in anticipation of the next patch release. Any bug fix applied to a release branch must first be applied to master (and branch-1 if applicable).

Feature branches are used to develop new features without destabilizing the rest of Hive. The intent of a feature branch is that it will be merged back into master once the feature has stabilized.

For general information about Hive branches, see Hive Versions and Branches.

Hadoop Dependencies

The Hive build downloads a number of different Hadoop versions via Maven in order to compile "shims" which allow for compatibility with these Hadoop versions. However, by default, the rest of Hive is only built and tested against a single Hadoop version (1.2.1 as of this writing, but check pom.xml for the latest).

The Maven build has two profiles, one for Hadoop 1 (0.20 and 1.X) and one for Hadoop 2 (2.X). By default the hadoop-1 profile is used; to use the hadoop-2 profile just specify "-Phadoop-2".

Trunk builds of Hive require Hadoop version at least 0.20.1; older versions are no longer supported.

Unit Tests

Please make sure that all unit tests succeed before and after applying your patch and that no new javac compiler warnings are introduced by your patch. Also see the information in the previous section about testing with different Hadoop versions if you want to verify compatibility with something other than the default Hadoop version.

When submitting a patch it's highly recommended you execute tests locally which you believe will be impacted in addition to any new tests. The full test suite can be executed by Hive PreCommit Patch Testing. Hive Developer FAQ describes how to execute a specific set of tests.

> cd hive-trunk
> mvn clean install -DskipTests -Phadoop-1
> mvn test -Dtest=SomeTest -Phadoop-1

After a while, if you see

[INFO] BUILD SUCCESS

all is ok, but if you see

[INFO] BUILD FAILURE

then you should fix things before proceeding.

Unit tests take a long time (several hours) to run sequentially even on a very fast machine; for information on how to run them in parallel, see Hive PreCommit Patch Testing.

Add a Unit Test

There are two kinds of unit tests in Hive:

  • Normal unit test: These are used by testing a particular component of Hive.
    • We just need to add a new class (name must start with "Test") in */src/test directory.
    • We can run "mvn test -Dtest=TestAbc -Phadoop-1" where TestAbc is the name of the new class. This will test only the new testcase, which will be faster than "mvn test -Phadoop-1" which tests all testcases.
  • A new query: If the new feature can be tested using Hive command line, we just need to add a new *.q file and a new *.q.out file:
    • If the feature is added in ql
      • Add a new XXXXXX.q file in ql/src/test/queries/clientpositive.
      • Run "mvn test -Phadoop-1 -Dtest=TestCliDriver -Dqfile=XXXXXX.q -Dtest.output.overwrite=true". This will generate a new XXXXXX.q.out file in ql/src/test/results/clientpositive.
        • If you want to run multiple .q files in the test run, you can specify comma separated .q files, for example -Dqfile="X1.q,X2.q". You can also specify a Java regex, for example -Dqfile_regex='join.*'. (Note that it takes Java regex, i.e., 'join.*' and not 'join*'). The regex match first removes the .q from the file name before matching regex, so specifying "join*.q" will not work.
      • If you are using hive-0.11.0 or later, you can specify "-Dmodule=ql".
    • If the feature is added in contrib
      • Do the steps above, replacing "ql" with "contrib", and "TestCliDriver" with "TestContribCliDriver".
      • If you are using hive-0.11.0 or later, you can specify "-Dmodule=contrib".

Debugging

Please see Debugging Hive code in Development Guide.

Creating a Patch

After you have committed a change or set of changes to your local repository, you need to create a patch to post on the JIRA. The naming convention for patches is:

HIVE-<JIRA-NUMBER>[.<patch-num>][-<branch-name>].patch

<patch-num> is only required if it is not the first patch.

<branch-name> is only required if it is not master. (See Understanding Hive Branches above.)

So the first patch for JIRA HIVE-9999 intended to be applied to master would be named "HIVE-9999.patch".

The second patch for the same JIRA would be named "HIVE-9999.2.patch".

A patch for the same JIRA intended to be applied to the llap branch would be named HIVE-9999-llap.patch".

git diff --no-prefix <commit> > HIVE-1234.1.patch

<commit> is the last commit from Hive (not you) before your commits. Note that if it has been a while since you fetched or pulled from the Hive repository, you may need to do a rebase to get your commit(s) on top in order to create a patch that will cleanly apply.

Please do not:

  • reformat code unrelated to the bug being fixed: formatting changes should be separate patches/commits;
  • comment out code that is now obsolete: just remove it;
  • insert comments around each change, marking the change: folks can use subversion to figure out what's changed and by whom;
  • make things public which are not required by end users.

Please do:

  • try to adhere to the coding style of files you edit;
  • comment code whose function or rationale is not obvious;
  • update documentation (e.g., package.html files, hive-default.xml.template, this wiki, and so on).

Attaching and Submitting a Patch

This section only gives the basic procedures for attaching and submitting a patch. See Contributing Your Work below for more information.

  1. Attach the patch file to a JIRA ticket: in the ticket's "More" tab, select "Attach Files" and use "Choose File" to upload the file, then add a descriptive comment.
  2. Put the patch in the review queue: click the "Submit Patch" button. The button name will change to "Cancel Patch" and the ticket status will change to Patch Available.

Updating a Patch

For patch updates, our convention is to number them like HIVE-1856.1.patch, HIVE-1856.2.patch, etc. And then click the "Submit Patch" button again when a new one is uploaded; this makes sure it gets back into the review queue.

Applying a Patch

To apply a patch that you either generated or found from JIRA, you can issue:

patch -p0 < cool_patch.patch

If you just want to check whether the patch applies you can run patch with --dry-run option:

patch -p0 --dry-run < cool_patch.patch

If you are an Eclipse user, you can apply a patch by:

  1. Right click project name in Package Explorer.
  2. Team -> Apply Patch.

Review Process

See Review Board for instructions.

  • Use Hadoop's code review checklist as a rough guide when doing reviews.
  • In JIRA, use 'Submit Patch' to get your review request into the queue.
  • If a committer requests changes, set the issue status to 'Resume Progress', then once you're ready, submit an updated patch with necessary fixes and then request another round of review with 'Submit Patch' again.
  • Once your patch is accepted, be sure to upload a final version which grants rights to the ASF.

Contributing Your Work

Finally, patches should be attached to an issue report in JIRA via the Attach File link on the issue's JIRA. Please add a comment that asks for a code review. Please note that the attachment should be granted license to ASF for inclusion in ASF works (as per the Apache License).

When you believe that your patch is ready to be committed, select the Submit Patch link on the issue's JIRA. Unit tests will run automatically if the file is named according to the naming standards. See Hive PreCommit Patch Testing. Tests should all pass. If your patch involves performance optimizations, they should be validated by benchmarks that demonstrate an improvement.

If your patch creates an incompatibility with the latest major release, then you must set the Incompatible change flag on the issue's JIRA and fill in the Release Note field with an explanation of the impact of the incompatibility and the necessary steps users must take.

If your patch implements a major feature or improvement, then you must fill in the Release Note field on the issue's JIRA with an explanation of the feature that will be comprehensible by the end user.

The Release Note field can also document changes in the user interface (such as new HiveQL syntax or configuration parameters) prior to inclusion in the wiki documentation.

A committer should evaluate the patch within a few days and either: commit it; or reject it with an explanation.

Please be patient. Committers are busy people too. If no one responds to your patch after a few days, please make friendly reminders. Please incorporate others' suggestions into your patch if you think they're reasonable. Finally, remember that even a patch that is not committed is useful to the community.

Should your patch receive a "-1" select Resume Progress on the issue's JIRA, upload a new patch with necessary fixes, and then select the Submit Patch link again.

Committers: for non-trivial changes, it is best to get another committer to review your patches before commit. Use the Submit Patch link like other contributors, and then wait for a "+1" from another committer before committing. Please also try to frequently review things in the patch queue.

JIRA Guidelines

Please comment on issues in JIRA, making your concerns known. Please also vote for issues that are a high priority for you.

Please refrain from editing descriptions and comments if possible, as edits spam the mailing list and clutter JIRA's "All" display, which is otherwise very useful. Instead, preview descriptions and comments using the preview button (icon below the comment box) before posting them. Keep descriptions brief and save more elaborate proposals for comments, since descriptions are included in JIRA's automatically sent messages. If you change your mind, note this in a new comment, rather than editing an older comment. The issue should preserve this history of the discussion.

To open a JIRA issue, click the Create button on the top line of the Hive summary page or any Hive JIRA issue. When in doubt about how to fill in the form, take a look at what was done for other issues. Note that Fix Version/s should not be tagged until an issue is closed, and then, it is tagged by the committer closing it to indicate which version the fix went into. Fix Version/s is not used to request which version it should go into – you can put such requests in the comments.

Here are some Hive JIRA issues that you can use as examples:

For examples that have not yet been committed, see the activity stream at the bottom of the Hive summary page or the list of most recent issues.

Generating Thrift Code

Some portions of the Hive code are generated by Thrift. For most Hive changes, you don't need to worry about this, but if you modify any of the Thrift IDL files (e.g. metastore/if/hive_metastore.thrift and service/if/hive_service.thrift), then you'll also need to regenerate these files and submit their updated versions as part of your patch.

Here are the steps relevant to hive_metastore.thrift:

  1. Don't make any changes to hive_metastore.thrift until instructed below.
  2. Use the approved version of Thrift. This is currently thrift-0.9.0, which you can obtain from http://thrift.apache.org/.
  3. Build the Thrift compiler from its sources, then install it:
    1. cd /path/to/thrift-0.9.0
    2. ./configure --without-csharp --without-ruby
    3. make
    4. sudo make install
  4. Before proceeding, verify that which thrift returns the build of Thrift you just installed (typically /usr/local/bin on Linux); if not, edit your PATH and repeat the verification. Also verify that the command 'thrift -version' returns the expected version number of Thrift.
  5. Now you can run the Maven 'thriftif' profile to generate the Thrift code:
    1. cd /path/to/hive-trunk/
    2. mvn clean install -Phadoop-1,thriftif -DskipTests -Dthrift.home=/usr/local
    3. If you see an error about fb303.thrift not being found, copy it to the appropriate directory and run above command again. On centOS/RHEL:
      cp /path/to/thrift-0.9.0/contrib/fb303/if/fb303.thrift /usr/local/share/fb303/if/fb303.thrift
  6. Use svn status to verify that the code generation was a no-op, which should be the case if you have the correct Thrift version and everyone has been following these instructions. If you can't figure out what is going wrong, ask for help from a committer.
  7. Now make your changes to hive_metastore.thrift, and then run the compiler again:
    1. mvn clean install -Phadoop-1,thriftif -DskipTests -Dthrift.home=/usr/local
  8. Now use svn status and svn diff to verify that the regenerated code corresponds only to the changes you made to hive_metastore.thrift. You may also need svn add if new files were generated (and svn remove if files have been obsoleted).
  9. cd /path/to/hive-trunk
  10. ant clean package
  11. Verify that Hive is still working correctly with both embedded and remote metastore configurations.

Stay Involved

Contributors should join the Hive mailing lists. In particular the dev list (to join discussions of changes) and the user list (to help others).

See Also

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