Spark Memory Management on EMR

Karunanithi Shanmugam gives us some tips on memory management for Spark in Amazon’s ElasticMapReduce:

Amazon EMR provides high-level information on how it sets the default values for Spark parameters in the release guide. These values are automatically set in the spark-defaults settings based on the core and task instance types in the cluster.

To use all the resources available in a cluster, set the maximizeResourceAllocation parameter to true. This EMR-specific option calculates the maximum compute and memory resources available for an executor on an instance in the core instance group. It then sets these parameters in the spark-defaults settings. Even with this setting, generally the default numbers are low and the application doesn’t use the full strength of the cluster. For example, the default for spark.default.parallelism is only 2 x the number of virtual cores available, though parallelism can be higher for a large cluster.

Spark on YARN can dynamically scale the number of executors used for a Spark application based on the workloads. Using Amazon EMR release version 4.4.0 and later, dynamic allocation is enabled by default (as described in the Spark documentation).

There’s a lot in here, much of which applies to Spark in general and not just EMR.