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Posted to hdfs-issues@hadoop.apache.org by "dhruba borthakur (JIRA)" <ji...@apache.org> on 2011/01/04 07:42:46 UTC
[jira] Created: (HDFS-1567) DFSClient should retry reading from all
datanodes in round robin fashion
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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[jira] Commented: (HDFS-1567) DFSClient should retry reading from
all datanodes in round robin fashion
Posted by "dhruba borthakur (JIRA)" <ji...@apache.org>.
[ https://issues.apache.org/jira/browse/HDFS-1567?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12977145#action_12977145 ]
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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