[ https://issues.apache.org/jira/browse/HDFS-5776?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13886107#comment-13886107 ]
stack commented on HDFS-5776: ----------------------------- [~jingzhao] Thanks for the new input. Please help me better understand what you mean by making more clean so we can adjust the patch accordingly. Hedged reads are set on or off in the client configuration xml and per DFSClient instance can be enabled/disabled as you go. Yes, you could read code and figure that it is possible to do some heavyweight gymnastics creating your own Configuration -- expensive -- and a new DFSClient -- ditto -- if you wanted to work around whatever is out in the configuration xml. That seems fine by me especially as there is no real means of shutting down this access route. Pardon me but I do not follow what you are asking for in 1. Maybe you are referring to a 'hole' where if the thread count is <= 0 on construction, the enable will have no effect -- and you want it to have an 'effect' post construction? For 2., you are suggesting that setThreadsNumForHedgedReads not be private but be available API for the DFSClient to toggle as it sees fit? I'll let @liang xie address your enoughNodesForHedgedRead comment. Thanks for checking back. > 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-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. -- This message was sent by Atlassian JIRA (v6.1.5#6160)