DFSClient should retry reading from all datanodes in round robin fashion
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Key: HDFS-1567
URL: https://issues.apache.org/jira/browse/HDFS-1567
Project: Hadoop HDFS
Issue Type: Improvement
Components: hdfs client
Reporter: dhruba borthakur
In the current implementation, the DFSClient retries the same datanode a few
times (for reading) before marking the datanode as "dead" and moving on to
trying the read-request from the next replica. This introduces additional delay
when the first candidate datanode was really out-of-service. Instead, it might
be beneficial (for performance) to make the DFSClient retry all datanode
replicas one after another (while keeping the total number of retries per
datanode the same as now); if all the replicas were tried unsuccessfully once,
then loop back to retrying the first one and so on.
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