What is Samza?
Apache Samza is a distributed stream processing framework. It uses Apache Kafka for messaging, and Apache Hadoop YARN to provide fault tolerance, processor isolation, security, and resource management.
Samza's key features include:
- Simple API: Unlike most low-level messaging system APIs, Samza provides a very simple callback-based "process message" API comparable to MapReduce.
- Managed state: Samza manages snapshotting and restoration of a stream processor's state. When the processor is restarted, Samza restores its state to a consistent snapshot. Samza is built to handle large amounts of state (many gigabytes per partition).
- Fault tolerance: Whenever a machine in the cluster fails, Samza works with YARN to transparently migrate your tasks to another machine.
- Durability: Samza uses Kafka to guarantee that messages are processed in the order they were written to a partition, and that no messages are ever lost.
- Scalability: Samza is partitioned and distributed at every level. Kafka provides ordered, partitioned, replayable, fault-tolerant streams. YARN provides a distributed environment for Samza containers to run in.
- Pluggable: Though Samza works out of the box with Kafka and YARN, Samza provides a pluggable API that lets you run Samza with other messaging systems and execution environments.
- Processor isolation: Samza works with Apache YARN, which supports Hadoop's security model, and resource isolation through Linux CGroups.
Check out Hello Samza to try Samza. Read the Background page to learn more about Samza.
Building Samza
To build Samza from a git checkout, run:
./gradlew clean build
To build Samza from a source release, it is first necessary to download the gradle wrapper script above. This bootstrapping process requires Gradle to be installed on the source machine. Gradle is available through most package managers or directly from its website. To bootstrap the wrapper, run:
gradle -b bootstrap.gradle
After the bootstrap script has completed, the regular gradlew instructions below are available.
Scala and YARN
Samza builds with Scala 2.10 and YARN 2.6.1, by default. Use the -PscalaVersion switches to change Scala versions. Samza supports building Scala with 2.10.
./gradlew -PscalaVersion=2.10 clean build
Testing Samza
To run all tests:
./gradlew clean test
To run a single test:
./gradlew clean :samza-test:test -Dtest.single=TestStatefulTask
To run key-value performance tests:
./gradlew samza-shell:kvPerformanceTest -PconfigPath=file://$PWD/samza-test/src/main/config/perf/kv-perf.properties
To run all integration tests:
./bin/integration-tests.sh <dir>
Running checkstyle on the java code
./gradlew checkstyleMain checkstyleTest
Job Management
To run a job (defined in a properties file):
./gradlew samza-shell:runJob -PconfigPath=file:///path/to/job/config.properties
To inspect a job's latest checkpoint:
./gradlew samza-shell:checkpointTool -PconfigPath=file:///path/to/job/config.properties
To modify a job's checkpoint (assumes that the job is not currently running), give it a file with the new offset for each partition, in the format systems.<system>.streams.<topic>.partitions.<partition>=<offset>:
./gradlew samza-shell:checkpointTool -PconfigPath=file:///path/to/job/config.properties \
-PnewOffsets=file:///path/to/new/offsets.properties
Developers
To get Eclipse projects, run:
./gradlew eclipse
For IntelliJ, run:
./gradlew idea
Contribution
To start contributing on Samza please read Rules and Contributor Corner. Notice that Samza git repository does not support git pull request.
Apache Software Foundation
Apache Samza is a top level project of the Apache Software Foundation.
