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From "John Zhuge (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11738) Hedged pread takes more time when block moved from initial locations
Date Fri, 18 Aug 2017 07:48:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11738?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16131867#comment-16131867
] 

John Zhuge commented on HDFS-11738:
-----------------------------------

The patch looks great! Only a few minor comments:
* Keep the old chooseDataNode with 2 parameters. A few changes can be avoided.
* DFSInputStream.java:836: typo, replace "Whether to refetch if no nodes to chose currently."
with "Whether to refetch if no node to choose from."
* TestPread:766: replace "maximum two failures" with "maximum " + maxFailures + " failures".

> Hedged pread takes more time when block moved from initial locations
> --------------------------------------------------------------------
>
>                 Key: HDFS-11738
>                 URL: https://issues.apache.org/jira/browse/HDFS-11738
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs-client
>            Reporter: Vinayakumar B
>            Assignee: Vinayakumar B
>         Attachments: HDFS-11738-01.patch, HDFS-11738-02.patch, HDFS-11738-03.patch, HDFS-11738-04.patch
>
>
> Scenario : 
> Same as HDFS-11708.
> During Hedge read, 
> 1. First two locations fails to read the data in hedged mode.
> 2. chooseData refetches locations and adds a future to read from DN3.
> 3. after adding future to DN3, main thread goes for refetching locations in loop and
stucks there till all 3  retries to fetch locations exhausted, which consumes ~20 seconds
with exponential retry time.



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