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Arpit Agarwal commented on HDFS-5776:
-------------------------------------
{quote}
I don't see why we wouldn't expose this setting. It doesn't give the client the ability to
do anything bad it couldn't already do. You can already try to open a zillion files at once
in order to attack the NameNode / DataNodes. Preventing denial-of-service attacks is not currently
something we try to do. And in the future, if we ever do try to prevent denial-of-service
attacks, I don't think having hedged reads makes that any more or less difficult than it would
otherwise be.
{quote}
[~cmccabe] I am thinking of carelessly configured settings, not a deliberate dos.
> 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-v4.txt, HDFS-5776-v5.txt,
HDFS-5776-v6.txt, HDFS-5776-v7.txt, HDFS-5776-v8.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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