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https://issues.apache.org/jira/browse/HDFS-5776?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13877173#comment-13877173
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Liang Xie commented on HDFS-5776:
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{quote}
Nit: Should the '60' below here:
+ Thread.sleep(60);
Be more related to the the '100' you pass as the
DFS_DFSCLIENT_HEDGED_READ_THRESHOLD_MILLIS config? Be half of whatever
DFS_DFSCLIENT_HEDGED_READ_THRESHOLD_MILLIS is? My concern is that someone could
change one of these settings not realizing they are related (they are, right)?
Is it possible that on a slow machine – such as apache jenkins – that we may
get a hedged read when we do not expect it ?
+ // assert that there were no hedged reads. 60ms + delta < 100ms
i.e. could this test turn flakey on a strained testing infrastructure?
{quote}
very good suggestion, i modfied the 100ms to 500ms and sleep interval now is
50ms, it should be enough at least to me:)
> 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-v2.txt, HDFS-5776-v3.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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