1. Apache Samza
Reliable Stream Processing Atop
Apache Kafka and Hadoop YARN
Jakob Homan
London HUG

2. Who I am
• Samza for five months
• Before that Hadoop, Hive, Giraph
• Say hi: @blueboxtraveler

3. Things we would like to do
(better)

4. Provide timely, relevant updates to your newsfeed

5. Update search results with new information as it appears

6. Sculpt metrics and logs into useful shapes

7. Tools?
RPC
Samza
Response latency
Milliseconds to minutes
Synchronous
Later. Possibly much later.

8. Frame(work) of reference
Storage layer
Execution
engine
Classic
Hadoop
HDFS
Map-Reduce
Samza
Kafka
YARN
API
map(k, v) => (k,v)
reduce(k, list(v)) => (k,v)
process(msg(k,v)) => msg(k,v)

9. Storage layer: Kafka

10. Apache Kafka
• Persistent,
reliable,
distributed
message queue
Shiny new logo!

11. At LinkedIn
10+ billion
writes per day
172k
messages per second
(average)
55+ billion
messages per day
to real-time consumers

12. Quick aside…
Kafka: First among (pluggable) equals
LinkedIn: Espresso and Databus
Coming soon? HDFS, ActiveMQ, Amazon SQS

13. Kafka in four bullet points
• Producers send messages to brokers
• Messages are key, value pairs
• Brokers store messages in topics for
consumers
• Consumers pull messages from brokers

14. A Kafka Topic
“The ref’s blind!”
534
“Car nicked!”
234
“Very sleepy”
755
534
Topic: StatusUpdateEvent
“Nicked a car!”
Value: Timestamp, new status, geolocation, etc.
Key: User ID of user who updated the status

15. For our purposes, hash partitioned on the key!
Key
Message
contents
Message
content
Key
Message
contents
Key
Message
contents
Message
contents
Key
Key
Message
contents
Key
Message
contents
Message
contents
Key
Partition 2
Key
Partition 1
Key
Partition 0
Message
contents
Key
Kafka topics are partitioned
Message
content

16. A Samza job
• StatusUpdateEvent
• NewConnectionEvent
• LikeUpdateEvent
MyStreamTask
implements StreamTask
{ …………. }
Input topics
Some code
• NewsUpdatePost
• UpdatesPerHourMetric
Output topics

17. Execution engine: YARN

18. What we use YARN for
• Distributing our tasks across multiple
machines
• Letting us know when one has died
• Distributing a replacement
• Isolating our tasks from each other

19. YARN: Execution and reliability
MyStreamTask:process()
Samza TaskRunner: Partition 0
Samza App Master
MyStreamTask:process()
Samza TaskRunner: Partition 1
Node Manager 1
Node Manager 2
Kafka Broker
Kafka Broker
Machine 1
Machine 1

20. Co-partitioning of topics
MyStreamTask:process()
StatusUpdateEvent, Partition 0
Samza TaskRunner: Partition 0
NewsUpdatePost
NewConnectionEvent, Partition 0
An instance of StreamTask is responsible for a specific partition

21. API: process()

22. getKey(), getMsg()
public interface StreamTask {
void process(IncomingMessageEnvelope envelope,
MessageCollector collector,
TaskCoordinator coordinator
)
sendMsg(topic, key, value)
}
commit(), shutdown()

23. Awesome feature: State
MyStreamTask:process()
Samza TaskRunner: Partition 0
Store state
• Generic data store interface
• Key-value out-of-box
– More soon? Bloom filter, lucene, etc.
• Restored by Samza upon task crash

24. (Pseudo)code snippet: Newsfeed
• Consume StatusUpdateEvent
– Send those updates to all your conmections via
the NewsUpdatePost topic
• Consume NewConnectionEvent
– Maintain state of connections to know who to
send to

25. public class NewsFeed implements StreamTask {
void process(envelope, collector, coordinator) {
msg = env.getMsg()
userId = msg.get(“userID”);
if(msg.get(“type”)==STATUS_UPDATE) {
foreach(conn: kvStore.get(userId) {
collector.send(“NewsUpdatePost”,
new Msg(conn, msg.get(“newStatus”))
}
} else {
newConn = msg.get(“newConnection”)
connections = kvStore.get(userId)
kvStore.put(userID, connections ++ newConn)
}

26. Current status

27. Hello, Samza!
Up and running in 3 minutes
Consume Wikipedia edits live
Generate stats on those edits
Cool, eh? bit.ly/hello-samza

28. samza.incubator.apache.org
bit.ly/samza_newbie_issues

29. Cheers!
•
•
•
•
•
Quick start: bit.ly/hello-samza
Project homepage: samza.incubator.apache.org
Newbie issues: bit.ly/samza_newbie_issues
Detailed Samza and YARN talk: bit.ly/samza_and_yarn
Twitter: @samzastream