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I recently upgraded to 0.16.2 from 0.15.2 on our 10 node cluster. Unfortunately we're seeing datanode timeout issues. In previous versions we've often seen in the nn webui that one or two datanodes "last contact" goes from the usual 0-3 sec to ~200-300 before it drops down to 0 again. This causes mild discomfort but the big problems appear when all nodes do this at once, as happened a few times after the upgrade. It was suggested that this could be due to namenode garbage collection, but looking at the gc log output it doesn't seem to be the case.
org.apache.hadoop.dfs.DataNode: PacketResponder blk_-9149681676832791404 2 Exception java.io.EOFException