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https://issues.apache.org/jira/browse/HDFS-5776?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13965839#comment-13965839
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Chris Nauroth commented on HDFS-5776:
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FYI, I've discovered that the {{DFSClient}} can hang infinitely if using hedged
reads and all eligible datanodes die. This bug is present in 2.4.0. I've
posted a patch on HDFS-6231 to fix it, hopefully for inclusion in 2.4.1.
> 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
> Fix For: 2.4.0
>
> Attachments: HDFS-5776-v10.txt, HDFS-5776-v11.txt, HDFS-5776-v12.txt,
> HDFS-5776-v12.txt, HDFS-5776-v13.wip.txt, HDFS-5776-v14.txt,
> HDFS-5776-v15.txt, HDFS-5776-v17.txt, HDFS-5776-v17.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,
> HDFS-5776v18.txt, HDFS-5776v21-branch2.txt, HDFS-5776v21.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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