How to Contribute to Hadoop Core
This page describes the mechanics of how to contribute software to Hadoop Core. For ideas about what you might contribute, please see the ProjectSuggestions page.
Getting the source code
First of all, you need the Hadoop source code.
Get the source code on your local drive using ![[WWW]](/wiki/modern/img/moin-www.png){kind=small}
SVN. Most development is done on the "trunk":
svn checkout http://svn.apache.org/repos/asf/hadoop/core/trunk/ hadoop-core-trunk
If you prefer to use Eclipse for development, there are instructions for setting up SVN access from within Eclipse at EclipseEnvironment.
Making Changes
Before you start, send a message to the Hadoop 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 (very) nice features using your favorite IDE.
But 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 one exception: Indent two spaces per level, not four.
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 ant test.
By default, do not let tests write any temporary files to /tmp. Instead, the tests should write to the location specified by the test.build.data system property.
If a HDFS cluster or a MapReduce cluster is needed by your test, please use org.apache.hadoop.dfs.MiniDFSCluster and org.apache.hadoop.mapred.MiniMRCluster, respectively. TestMiniMRLocalFS is an example of a test that uses MiniMRCluster.
Place your class in the src/test tree.
TestFileSystem.java and TestMapRed.java are examples of standalone MapReduce-based tests.
TestPath.java is an example of a non MapReduce-based test.
You can run all the unit test with the command ant test, or you can run a specific unit test with the command ant -Dtestcase=<class name without package prefix> test (for example ant -Dtestcase=TestFileSystem test)
Generating a patch
Unit Tests
Please make sure that all unit tests succeed before constructing your patch and that no new javac compiler warnings are introduced by your patch.
> cd hadoop-core-trunk > ant -Djavac.args="-Xlint -Xmaxwarns 1000" clean test tar
After a while, if you see
BUILD SUCCESSFUL
all is ok, but if you see
BUILD FAILED
then please examine error messages in build/test and fix things before proceeding.
Javadoc
Please also check the javadoc.
> ant javadoc > firefox build/docs/api/index.html
Examine all public classes you've changed to see that documentation is complete, informative, and properly formatted. Your patch must not generate any javadoc warnings.
Creating a patch
Check to see what files you have modified with:
svn stat
Add any new files with:
svn add src/.../MyNewClass.java svn add src/.../TestMyNewClass.java
Edit the CHANGES.txt file, adding a description of your change, including the bug number it fixes. If this is a new feature, or other enhancement that doesn't currently have a ticket please create one for it, then use it's number when adding your note to CHANGES.txt. You'll need this ticket to submit your patch anyway.
In order to create a patch, type:
svn diff > myBeautifulPatch.patch
This will report all modifications done on Hadoop sources on your local disk and save them into the myBeautifulPath.patch file. Read the patch file. Make sure it includes ONLY the modifications required to fix a single issue.
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, this wiki, etc.)
Testing your patch
Before submitting your patch, you are encouraged to run the same tools that the automated Hudson patch test system will run on your patch. This enables you to fix problems with your patch before you submit it. The test-patch Ant target will run your patch through the same checks that Hudson currently does except for executing the core and contrib unit tests.
To use this target, you must run it from a clean workspace (ie svn stat shows no modifications or additions). From your clean workspace, run:
ant \ -Dpatch.file=/patch/to/my.patch \ -Dforrest.home=/path/to/forrest/ \ -Dfindbugs.home=/path/to/findbugs \ -Dscratch.dir=/path/to/a/temp/dir \ (optional) -Dsvn.cmd=/path/to/subversion/bin/svn \ (optional) -Dgrep.cmd=/path/to/grep \ (optional) -Dpatch.cmd=/path/to/patch \ (optional) test-patch
At the end, you should get a message on your console that is similar to the comment added to Jira by Hudson's automated patch test system. The scratch directory (which defaults to the value of ${user.home}/tmp) will contain some output files that will be useful in determining what issues were found in the patch.
Some things to note:
the optional cmd parameters will default to the ones in your PATH environment variable
the grep command must support the -o flag (GNU does)
the patch command must support the -E flag
Applying a patch
To apply a patch either you 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
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 following our code review checklist. Please note that the attachment should be granted license to ASF for inclusion in ASF works (as per the Apache License ยง5).
When you believe that your patch is ready to be committed, select the Submit Patch link on the issue's Jira. Submitted patches will be automatically tested against "trunk" by Hudson, the project's continuous integration engine. Upon test completion, Hudson will add a success ("+1") message or failure ("-1") to your issue report in Jira. If your issue contains multiple patch versions, Hudson tests the last patch uploaded.
Folks should run ant clean test javadoc checkstyle before selecting Submit Patch. Tests should all pass. Javadoc should report no warnings or errors. Checkstyle's error count should not exceed that listed at Checkstyle Errors Hudson's tests are meant to double-check things, and not be used as a primary patch tester, which would create too much noise on the mailing list and in Jira. Submitting patches that fail Hudson testing is frowned on, (unless the failure is not actually due to the patch).
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.
Once a "+1" comment is received from the automated patch testing system and a code reviewer has set the Reviewed flag on the issue's Jira, a committer should then evaluate it 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 other's 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" from the Hudson testing, select the 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 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 their 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 (on the right) 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.
Stay involved
Contributors should join the Hadoop mailing lists. In particular, the commit list (to see changes as they are made), the dev list (to join discussions of changes) and the user list (to help others).