Details
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Improvement
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Status: Resolved
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Major
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Resolution: Not A Problem
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All
Description
Currently Hadoop spawns a single threaded JVM for each task. While good for many tasks, this does not maximize resource usage for slaves that have many cores (machines with more cores are getting more cost effective everyday) and are running jobs that require many gigabytes of read-only in-memory resources to maximize throughput. Running in separate JVMs requires redundantly loading large amounts of data, reducing the possible number of parallel tasks that can run per a machine even though more cpus are available.
Adding this ability will give hadoop users the flexibility to balance their need for maximizing memory usage & throughput and task segmentation.
Note: This is a blocking bug in porting processes over to hadoop for my own organization. I am testing a patch for this now that leaves the existing behavior for single threaded operation in-tact. All synchronization is done through wrapper classes and helper methods and should not add any overhead to non-threaded processes.
