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stack commented on HDFS-5776: ----------------------------- bq. An alternative way to do this is to have an "Allow-Hedged-Reads" configuration, and if it is set to true, we load the number of thread pool and the threshold time. We will provide an isHedgedReadsEnabled method but we will not provide enable/disable methods. The reviews are great. On the above, while I can see putting the on/off switch as a DN config., we should allow setting at least the config on when to start the hedge read per DFSCient instance. bq. This means that we do need to put this in a static, for now, or else FileContext users will be constantly destroying and creating thread-pools. Thanks Colin. Makes sense. > 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.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. -- This message was sent by Atlassian JIRA (v6.1.5#6160)