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When you change the number of spark slaves, you may also want to update the property spark.default.parallellism in the service configuration. This is to optimize the performance of the Spark cluster. However, in order for the change in the Spark configuration to become effective you must restart the cluster and submit the spark application. For further information about spark.default.parallellism, see 4.3 KPI Management - External Software.
If the Spark UI indicates that a worker has status "DEAD", you must restart the cluster.
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