[
https://issues.apache.org/jira/browse/HDFS-5776?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13883079#comment-13883079
]
Colin Patrick McCabe commented on HDFS-5776:
--------------------------------------------
bq. Fine, let me introduce a hard code up-limit for
DFS_DFSCLIENT_HEDGED_READ_THREADPOOL_SIZE to 128.
Please don't. There's no reason to put arbitrary limits into the code. We
don't do this with any other configuration settings. At some point, you have
to trust the configuration.
bq. we don't need to restart DN/RS or sth else, we can modify/introduce a hbase
shell script to disable/enable the feature per instance or modify the thread
number or other requirements, i think it's feasible, and those works, in deed,
are the major task for supporting hedged read in HBase side
Are you suggesting that we make the thread number setting changeable at
runtime? That seems like a good idea, but probably something we should do as a
follow-on JIRA.
> 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-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)
