What's the meaning of "Locality Level"on Spark cluster - Stack Overflow

What's the meaning of "Locality Level"on Spark cluster - Stack Overflow

With respect to the different levels PROCESS_LOCAL, NODE_LOCAL, RACK_LOCAL, or ANY I think the methods findTask and findSpeculativeTask in org.apache.spark.scheduler.TaskSetManager illustrate how Spark chooses tasks based on their locality level. It first will check for PROCESS_LOCAL tasks which are going to be launched in the same executor process. If not, it will check for NODE_LOCAL tasks that may be in other executors in the same node or it need to be retrieved from systems like HDFS, cached, etc. RACK_LOCAL means that data is in another node and therefore it need to be transferred prior execution. And finally, ANY is just to take any pending task that may run in the current node.

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