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https://issues.apache.org/jira/browse/HDFS-1567?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12977145#action_12977145
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dhruba borthakur commented on HDFS-1567:
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Just to elaborate, the above is applicable only for *retries* and retries occur
when the client encounters errors while reading a block from a datanode.
> DFSClient should retry reading from all datanodes in round robin fashion
> ------------------------------------------------------------------------
>
> 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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