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Subject [CONF] Apache Mahout > How To Contribute
Date Mon, 10 Jun 2013 06:57:00 GMT
Space: Apache Mahout (
Page: How To Contribute (

Edited by Robin Anil:
"Contributing" to an Apache project is about more than just writing code -- it's about doing
what you can to make the project better.  There are lots of ways to contribute....


h2. Be Involved

Contributors should join the [Mahout mailing lists|].
 In particular:
* The user list (to help others)
* The commit list (to see changes as they are made)
* The dev list (to join discussions of changes)  -- This is the best place to understand where
we are headed.

Please keep discussions about Mahout on list so that everyone benefits.  Emailing individual
committers with questions about specific Mahout issues is discouraged.  See [].

You can also [track issues that you've raised|]
in JIRA.

h2. What to Work On?

What do you like to work on?  There are a ton of things in Mahout that we would love to have
contributions for.  Data ingestion, data visualization, documentation, new algorithms, performance
improvements, better tests, etc.  The best place to start is by looking in JIRA under the
Mahout project and seeing what bugs have been reported and seeing if any look like you could
take them on.  Small, well written, well tested patches are a great way to get your feet wet.
 It could be something as simple as fixing a typo.  The more important piece is you are showing
you understand the necessary steps for making changes to the code.  Mahout is a pretty big
beast at this point, so changes, especially from non-committers, need to be evolutionary not
revolutionary since it is often very difficult to evaluate the merits of a very large patch.
 Think small, at least to start\!

Beyond JIRA, hang out on the dev@ mailing list.  That's where we discuss what we are working
on in the internals and where you can get a sense of where people are working.

Also, documentation is a great way to familiarize yourself with the code and is always a welcome
addition to the codebase and to this Wiki.

Also, check out the [MAHOUT_INTRO_CONTRIBUTE|]
items in JIRA, as these have been deemed to be fairly easy to start on.

Also feel free to jump in on the [backlog|]
or on a the [next version|]

If you are interested in working towards being a committer, [general guidelines are available

h2. Contributing Code (Features, Big Fixes, Tests, etc...)

This section identifies the ''optimal'' steps community member can take to submit a changes
or additions to the Mahout code base.  This can be new features, bug fixes optimizations of
existing features, or tests of existing code to prove it works as advertised (and to make
it more robust against possible future changes).

Please note that these are the "optimal" steps, and community members that don't have the
time or resources to do everything outlined on this below should not be discouraged from submitting
their ideas "as is" per "Yonik Seeley's (Solr committer) Law of Patches" ...

A half-baked patch in Jira, with no documentation, no tests
and no backwards compatibility is better than no patch at all.

Just because you may not have the time to write unit tests, or cleanup backwards compatibility
issues, or add documentation, doesn't mean other people don't. Putting your patch out there
allows other people to try it and possibly improve it.

h3. Getting the source code

First of all, you need the Mahout source code.

Get the source code on your local drive using [SVN|].
 Most development is done on the "trunk":

> svn checkout [] mahout-trunk

Note that committers have to use https instead of http here, but http is fine for read-only
access to the trunk code.

h3. Making Changes

Before you start, you should send a message to the [Mahout developer mailing list|]
(Note: you have to subscribe before you can post), or file a bug 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|].
* 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.

h3. Generating a patch

A "patch file" is the format that all good contributions come in.  It bundles up everything
that is being added, removed, or changed in your contribution.

h4. Unit Tests

Please make sure that all unit tests succeed before constructing your patch.

> cd mahout-trunk
> mvn clean test
After a while, if you see
all is ok, but if you see
please, read carefully the errors messages and check your code.

h4. Creating the patch file

Check to see what files you have modified with:
svn stat

Add any new files with:
svn add src/.../

Subversions "add" command only modifies your local copy, so it doess not require commit permissions.
 By using "svn add", your entire comtribution can be included in a single patch file, without
needing to submit a seperate set of "new" files.

Edit the ''CHANGES.txt'' file, adding a description of your change, including the bug number
it fixes.

In order to create a patch, just type:

svn diff > MAHOUT-$issuenumber.patch

$issuenumber here should be the number of the JIRA issue the patch is supposed to fix. This
will report all modifications done on Mahout sources on your local disk and save them into
the ''MAHOUT-$issuenumber.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.)

h4. Contributing your work

Finally, patches should be attached to a bug report in [Jira|].
 If you are revising an existing patch, please re-use the exact same name as the previous
attachment, Jira will "grey out" the older versions so it's clear which version is the newest.

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 into
your patch if you think they're reasonable.  Finally, remember that even a patch that is not
committed is useful to the community.

h1. Review/Improve Existing Patches

If there's a Jira issue that already has a patch you think is really good, and works well
for you -- please add a comment saying so.   If there's room for improvement (more tests,
better javadocs, etc...) then make the changes and attach it as well.  If a lot of people
review a patch and give it a thumbs up, that's a good sign for committers when deciding if
it's worth spending time on the patch -- and if other people have already put in effort to
improve the docs/tests for a patch, that helps even more.

h2. Applying a patch

>From the base directory (assuming that is where the patch is generated from), run:
patch -p 0 -i <PATH TO PATCH> [--dry-run]

h1. Helpful Resources

The following resources may prove helpful when developing Mahout contributions.  (These are
not an endorsement of any specific development tools).  Note, these are the same code styles
that Lucene and Solr use.

* [Eclipse codestyle.xml file for Mahout's coding conventions, same as Lucene|]

* [IntelliJ IDEA codestyle.xml file for Mahout's coding conventions|]
(deprecated - Please don't use this. You are welcome to change this file to match the checkstyle
and remove this notice)

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