Drizzle is a low latency execution engine for Apache Spark that is targeted at stream processing and iterative workloads. Currently, Spark uses a BSP computation model, and notifies the scheduler at the end of each task. Invoking the scheduler at the end of each task adds overheads and results in decreased throughput and increased latency.

In Drizzle, we introduce group scheduling, where multiple batches (or a group) of computation are scheduled at once. This helps decouple the granularity of task execution from scheduling and amortize the costs of task serialization and launch.

The current Drizzle prototype exposes a low level API using the runJobs method in SparkContext. This method takes in a Seq of RDDs and corresponding functions to execute on these RDDs. Examples of using this API can be seen in DrizzleSingleStageExample and DrizzleRunningSum.

To try out Drizzle locally, we first build Spark based on existing instructions. For example, using SBT we can run

  ./build/sbt package

We can run then run the DrizzleRunningSum example with 4 cores for 10 iterations with group size 10. Note that this example requires at least 4GB of memory on your machine.

  ./bin/run-example --master "local-cluster[4,1,1024]" org.apache.spark.examples.DrizzleRunningSum 10 10

To compare this with existing Spark, we can run the same 10 iterations but now with a group size of 1

  ./bin/run-example --master "local-cluster[4,1,1024]" org.apache.spark.examples.DrizzleRunningSum 10 1

The benefit from using Drizzle is more apparent on large clusters. Results from running the single stage benchmark for 100 iterations on a Amazon EC2 cluster of 128 machines is shown below.

The source code in this repository is a research prototype and only implements the scheduling techniques described in our paper. The existing Spark unit tests pass with our changes and we are actively working on adding more tests for Drizzle. We are also working towards a Spark JIRA to discuss integrating Drizzle with the Apache Spark project.

Finally we would like to note that extensions to integrate Structured Streaming and Spark ML will be implemented separately.

For more details about the architecture of Drizzle please see our Spark Summit 2015 Talk and our Technical Report

This is joint work with Aurojit Panda, Kay Ousterhout, Mike Franklin, Ali Ghodsi, Ben Recht and Ion Stoica from the AMPLab at UC Berkeley.