How to change number of executors in local mode?

Question

Is it possible to set multiple executors for Spark Streaming application in a local mode using some Spark Conf settings? For now, I can not see any changes in Spark UI in terms of performance or executors number increase when I change spark.executor.instances parameter to 4, for example.

Answer 1

Local mode is a development tool, where all components are simulated in a single machine. Since single JVM mean single executor changing of the number of executors is simply not possible, and spark.executor.instances is not applicable.

All you can do in local mode is to increase number of threads by modifying the master URL - local[n] where n is the number of threads.

Answer 2

local mode is by definition "pseudo-cluster" that runs in Single JVM. That means maximum number of executors is 1.

If you want to experiment with multiple executors on local machine, what you can do is to create cluster with couple workers running on your local machine. Number of running instances is max number of executors for your tasks.

Answer 3

spark.executor.instances is not honoured in local mode.

Reference - https://books.japila.pl/apache-spark-internals/local/?h=local

Local-Mode: In this non-distributed single-JVM deployment mode, Spark spawns all the execution components - driver, executor, LocalSchedulerBackend, and master - in the same single JVM. The default parallelism is the number of threads as specified in the master URL. This is the only mode where a driver is used for execution.

So you can increase number of threads in JVM to n by passing master url as local[n].