[jira] [Updated] (HDFS-5776) Support 'hedged' reads in DFSClient

["stack (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-5776?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

stack updated HDFS-5776:
------------------------

    Attachment: HDFS-5776-v13.wip.txt

Addressing Jing Zhao's concerns.  Removed all the setters, redo of enoughNodesForHedgedReads, and fix an issue w/ the countdown latch.  Not done yet (Test in TestPread fails) and looking to add more....

> Support 'hedged' reads in DFSClient
> -----------------------------------
>
>                 Key: HDFS-5776
>                 URL: https://issues.apache.org/jira/browse/HDFS-5776
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client
>    Affects Versions: 3.0.0
>            Reporter: Liang Xie
>            Assignee: Liang Xie
>         Attachments: HDFS-5776-v10.txt, HDFS-5776-v11.txt, HDFS-5776-v12.txt, HDFS-5776-v12.txt, HDFS-5776-v13.wip.txt, HDFS-5776-v2.txt, HDFS-5776-v3.txt, HDFS-5776-v4.txt, HDFS-5776-v5.txt, HDFS-5776-v6.txt, HDFS-5776-v7.txt, HDFS-5776-v8.txt, HDFS-5776-v9.txt, HDFS-5776.txt
>
>
> This is a placeholder of hdfs related stuff backport from https://issues.apache.org/jira/browse/HBASE-7509
> The quorum read ability should be helpful especially to optimize read outliers
> we can utilize "dfs.dfsclient.quorum.read.threshold.millis" & "dfs.dfsclient.quorum.read.threadpool.size" to enable/disable the hedged read ability from client side(e.g. HBase), and by using DFSQuorumReadMetrics, we could export the interested metric valus into client system(e.g. HBase's regionserver metric).
> The core logic is in pread code path, we decide to goto the original fetchBlockByteRange or the new introduced fetchBlockByteRangeSpeculative per the above config items.



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