AWS EMR Spark – Much Larger Executors are Created than Requested

Starting EMR 5.32 and EMR 6.2 you can notice that Spark can launch much larger executors that you request in your job settings.

For example - We started a Spark Job with

spark.executor.cores = 4

But, one can see that the executors with 20 cores (instead of 4 as defined by spark.executor.cores) were launched.

The reason for allocating larger executors is that there is a AWS specific Spark option spark.yarn.heterogeneousExecutors.enabled (exists in EMR only, does not exist in Open Source Spark) that is set to true by default that combines multiple executor creation requests on the same node into a larger executor container.

So as the result you have fewer executor containers than you expected, each of them has more memory and cores that you specified.

If you disable this option (--conf "spark.yarn.heterogeneousExecutors.enabled=false"), EMR will create containers with the specified spark.executor.memory and spark.executor.cores settings and will not coalesce them into larger containers.

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