Getting started contributing to Apache Spark

Effectively Contributing to
Apache Spark
Beyond the Code Toronto 2016
This talk (as with all) represents my own personal views may not reflect that of the project.
I am not a Spark committer - but I’ve been contributing for 3 years

Who am I?
Holden
● Prefered pronouns: she/her
● Co-author of the Learning Spark & High Performance Spark books
● Software Engineer at IBM’s Spark Technology Center
● 100+ Spark Commits
● @holdenkarau
● http://www.slideshare.net/hkarau
● https://www.linkedin.com/in/holdenkarau

What we are going to explore together!
Getting a change into Apache Spark & the components
involved:
● Different ways to contribute
● Places to find things to contribute
● Tooling around code & doc contributions

How can we contribute to Spark?
● Direct code in the Apache Spark code base
● Code in packages built on top of Spark
● Yak shaving (aka fixing things that Spark uses)
● Documentation improvements & examples
● Books, Talks, and Blogs
● Answering questions (mailing lists, stack overflow, etc.)

Which is right for you?
● Direct code in the Apache Spark code base
○ High visibility, some things can only really be done here
○ Can take a lot longer to get changes in
● Code in packages built on top of Spark
○ No real review (+/-)
○ Really great for things like formats or standalone features
● Yak shaving (aka fixing things that Spark uses)
○ Super important to do sometimes - can take even longer to get in

Which is right for you? (continued)
● Documentation improvements & examples
○ Lots of places to contribute - mixed visibility - large impact
● Books, Talks, and Blogs
○ The documentation version of Spark Packages (e.g. no need for
community review)
○ Can be high visibility
○ Talk to me if you are thinking of writing a technical book :)

But before we get too far:
● Spark wishes to maintain compatibility between releases
● 2.0 just shipped - so most APIs should be stable
○ Notable exceptions include Structured Streaming
● It’s very important to talk about large code changes with
the key members before doing them
○ dev list is the simplest way of reaching out
○ Wonder who the key members are? Check the component maintainers on
https://cwiki.apache.org/confluence/display/SPARK/Committers

Adventure path 1: Direct to Spark
● Maybe we encountered a bug we want to fix
● Maybe we’ve got a feature we want to add
● Either way we should see if other people are doing it
● And if what we want to do is complex, it might be better
to find something simple to start with
● It’s dangerous to go alone - take this
https://cwiki.apache.org/confluence/display/SPARK/Contrib
uting+to+Spark

Getting the code
This step can take some time - especially over conference
WiFi so let's get it started now :)
Conference WiFi isn’t working out for you? Ask me and I can
make a copy of the repo to a USB stick for you :)

Exercise time
Photo by recastle

Spark’s Github (Exercise 1)
● https://github.com/apache/spark
● Make a fork of it
● Clone it locally

Getting started contributing to Apache Spark

JIRA - Issue tracking funtimes
● It’s like bugzilla or fog bugz
● There is an Apache JIRA for all Apache projects
● You can (and should) sign up for an account
● All changes in Spark (now) require a JIRA
● https://www.youtube.com/watch?v=ca8n9uW3afg
● Check it out at:
○ https://issues.apache.org/jira/browse/SPARK

The different pieces of Spark
Apache Spark
SQL &
DataFrames
Streaming
Language
APIs
Scala,
Java,
Python, &
R
Graph
Tools
Spark ML
bagel &
Graph X
MLLib
Community
Packages

The different pieces of Spark: 2.0+
Apache Spark
SQL &
DataFrames
Streaming
Language
APIs
Scala,
Java,
Python, &
R
Graph
Tools
Spark
ML
bagel &
Graph X
MLLib
Community
Packages
Structured
Streaming

What we can do with ASF JIRA?
● Search for issues (remember to filter to Spark project)
● Create new issues
○ search first to see if someone else has reported it
● Comment on issues to let people know we are working on it
● Ask people for clarification or help
○ e.g. “Reading this I think you want the null values to be replaced by
a string when processing - is that correct?”
○ @mentions work here too

What can’t we do with ASF JIRA?
● Assign issues (to ourselves or other people)
○ In lieu of assigning we can “watch” & comment
● Post long design documents (create a Google Doc & link to
it from the JIRA)
● Tag issues
○ While we can add tags, they often get removed

Finding a good “starter” issue:
● There are explicit starter tags in JIRA we can search for
● But often the starter tag isn’t applied
● Read through and look for simple issues
● Pick something in the same component you eventually want
to work in
○ And or consider improving the non-Scala language API for the
component(s) you want to work on.
● Look at the reporter and commenters - is there a
committer or someone whose name you recognize?
● Leave a comment that says you are going to start working
on this

Exercise 2: Find an issue you want to work on
https://issues.apache.org/jira/browse/SPARK
Also grep for TODO in components you are interested in (e.g.
grep -r TODO ./python/pyspark or grep -R TODO ./core/src)
Look between language APIs and see if anything is missing
that you think is interesting -
http://spark.apache.org/docs/latest/api/scala/index.html#org
.apache.spark.package
http://spark.apache.org/docs/latest/api/python/index.html
Feel free to work in groups :)

Exercise 3a: Building Spark
./build/sbt
or
./build/mvn
Working in Python? Make sure to build the package target so
your Python code will run :)
You can quickly verify build with the Spark Shell :)

What about documentation changes?
● Still use JIRAs to track
● We can’t edit the wiki :(
● But a lot of documentations lives in docs/*.md

Exercise 3b: Building Spark’s docs
./docs/README.md has a lot of info - but quickly:
SKIP_API=1 jekyll build
SKIP_API=1 jekyll serve --watch

Finding your way around the code
● Organized into sub-projects by directory
● IntelliJ is very popular with Spark developers
○ The free version is fine
● Some people like using emacs + ensime or magit too
● Language specific code is in each sub directory

Testing the issue
The spark-shell can often be a good way to verify the issue
reported in the JIRA is still occurring and come up with a
reasonable test.
Once you’ve got a handle on the issue in the spark-shell (or
if you decide to skip that step) check out
./[component]/src/test for Scala or doctests for Python

After we get our code working
(or even better while we work on it)
● Remember to follow the style guides
○ https://cwiki.apache.org/confluence/display/SPARK/Spark+Code+Style+Gu
ide
● Please always add tests
○ For development we can run scala test with “sbt [module]/testOnly”
○ In python we can specify module with ./python/run-tests
● ./dev/lint-scala & ./dev/lint-python check for some style
● Changing the API? Make sure we pass MiMa!
○ Sometimes its OK to make breaking changes, and MiMa can be a bit
overzealous so adding exceptions is common

A bit more on MiMa
● Spark wishes to maintain binary compatibility
○ in non-experimental components
● MiMa exclusions can be added if we verify (and document
how we verified) the compatibility
● Often MiMa is a bit over sensitive so don’t feel stressed
- feel free to ask for help if confused

Exercise 4: Open your editors
No arguing about which editor please - kthnx
Making a doc change? Look inside docs/*.md
Making a code change? grep or intellij or github inside
project codesearch can all help you find what you're looking
for.

Yay! Let’s make a PR :)
● Push to your branch
● Visit github
● Create PR (put JIRA name in title as well as component)
○ Components control where our PR shows up in
https://spark-prs.appspot.com/
● If you’ve been whitelisted tests will run
● Otherwise will wait for someone to verify
● Tag it “WIP” if its a work in progress (but maybe wait)
[puamelia]

Code review time
● Note: this is after the pull request creation
● I believe code reviews should be done in the open
○ With an exception of when we are deciding if we want to try and
submit a change
○ Even then should have hopefully decided that back at the JIRA stage
● My personal beliefs & your org’s may not align
Mitchell
Joyce

And now onto the actual code review...
● Most often committers will review your code (eventually)
● Other people can help too
● People can be very busy (check the release schedule)
● If you don’t get traction try pinging people
○ Me ( @holdenkarau - I can’t merge your code but I can take a look)
○ The author of the JIRA (even if not a committer)
○ The shepherd of the JIRA (if applicable)
○ The person who wrote the code you are changing (git blame)
○ Active committers for the component
Mitchell
Joyce

What does the review look like?
● LGTM - Looks good to me
○ Individual thinks the code looks good - ready to merge (sometimes
LGTM pending tests or LGTM but check with @[name]).
● SGTM - Sounds good to me (normally in response to a
suggestion)
● Sometimes get sent back to the drawing board
● Not all PRs get in - its ok!
○ Don’t feel bad & don’t get discouraged.
● Mixture of in-line comments & general comments

That’s a pretty standard small PR
● It took some time to get merged in
● It was fairly simple
● Review cycles are long - so move on to other things
● Only two reviewers
● Apache Spark Jenkins comments on build status :)
○ “Jenkins retest this please” is great
● Big PRs - like making PySpark pip installable can have >
10 reviewers and take a long time
● Sometimes it can be hard to find reviewers - tag your PRs
& ping people on github

Don’t get discouraged
David Martyn Hunt
It is normal to not get every pull request accepted
Sometimes other people will “scoop” you on your
pull request
Sometimes people will be super helpful with your
pull request

So who was that “Spark QA”?
● Automated pull request builder
● Jenkins based
● Runs all of the tests & style checks
● Lives in Berkeley
● Test logs live on, artifacts not so much
● https://amplab.cs.berkeley.edu/jenkins

Some changes require even more testing
● spark-perf (common for ML changes)
● spark-sql-perf (common for SQL changes)
● spark-integration-tests (integration testing)

While we are waiting:
● Keep merging in master when we get out of sync
● If we don’t jenkins can’t run :(
● We get out of sync surprisingly quickly!
● If our pull request gets older than 30 days it might get
auto-closed

So review: Where do we get started?
● Search for “starter” on JIRA
● Look on the mailing list for problems
● Stackoverflow - lots of questions some of which are bugs
● grep TODO broken FIXME
● Compare APIs between languages
● Customer/user reports?

But what about when we want to make big changes?
● Talk with the community
○ Developer mailing list dev@spark.apache.org
○ User mailing list user@spark.apache.org
● Create a public design document (google doc normally)
● Consider if it can be published as a spark-package
instead

Other resources:
● “Contributing to Apache Spark” -
https://cwiki.apache.org/confluence/display/SPARK/Contrib
uting+to+Spark
● Programming guide (along with JavaDoc, PyDoc, ScalaDoc,
etc.)
○ http://spark.apache.org/docs/latest/

What about creating a package?
● Relatively simple - need to publish to maven central
● Listed on http://spark-packages.org
● Cross building (Spark versions) not super easy
● If your building with sbt check out
https://github.com/databricks/sbt-spark-package to make
it easy to publish
● Used to do API compatibility checks
● Sometimes flakey - just republish if it doesn’t go
through

Signing your packages
● Required
● Can be a bit odd (sbt-pgp plugin has issues sometimes
with keys with passphrases)

What things can be good Spark packages?
● Input formats (especially Spark SQL, Streaming)
● Machine learning pipeline components & algorithms
● Testing support
● Monitoring data sinks
● Deployment tools

How about writing a book?
● Can be lots of fun
● Can also take up 100% of your “free” time
● Can get you invited to more nerd parties
● Most of the publisher are looking to improve/broaden
their Spark book line up
● Like an old book that hasn’t been updated? Talk to the
publisher about updating it.

Spark Videos
● Apache Spark Youtube Channel
● My Spark videos on YouTube -
○ http://bit.ly/holdenSparkVideos
● Spark Summit 2014 training
● Paco’s Introduction to Apache Spark

Learning Spark
Fast Data
Processing with
Spark
(Out of Date)
Fast Data
Processing with
Spark
(2nd edition)
Advanced
Analytics with
Spark
Coming soon:
Spark in Action

Learning Spark
Fast Data
Processing with
Spark
(Out of Date)
Fast Data
Processing with
Spark
(2nd edition)
Advanced
Analytics with
Spark
Coming soon:
Spark in Action
Early Release
High Performance Spark

And the next book…..
First five chapters are available in “Early Release”*:
● Buy from O’Reilly - http://bit.ly/highPerfSpark
Get notified when updated & finished:
● http://www.highperformancespark.com
● https://twitter.com/highperfspark
* Early Release means extra mistakes, but also a chance to help us make a more awesome
book.

And some upcoming talks:
● September
○ This meetup (yay)!
○ Toronto - Beyond the Code (Contributing to Spark)
○ New York City Strata Conf (Structured Streaming & Machine Learning)
● October
○ PyData DC - Making Spark go fast in Python (vroom vroom)
○ Salt Lake City Spark Meetup - TBD
○ London - OSCON - Getting Started Contributing to Spark
● December
○ Strata Singapore (Introduction to Datasets)

k thnx bye!
If you care about Spark testing and
don’t hate surveys:
http://bit.ly/holdenTestingSpark
Will tweet results
“eventually” @holdenkarau
Any PySpark Users: Have some
simple UDFs you wish ran faster
you are willing to share?:
http://bit.ly/pySparkUDF
Pssst: Have feedback on the workshop? Give me a shout
(holden@pigscanfly.ca) if you feel comfortable doing so :)

Getting started contributing to Apache Spark

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