[jira] [Commented] (HDFS-6591) while loop is executed tens of thousands of times in Hedged Read

["Liang Xie (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-6591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14041856#comment-14041856 ] 

Liang Xie commented on HDFS-6591:
---------------------------------

Yes, it's a valid bug report, just verified on my box.[~cnauroth] The fix from HDFS-6231 has a minor side effect(the original behavior is countDown only after a successful actualGetFromOneDataNode call): since we moved the latch to finaly statement. then once a actualGetFromOneDataNode() failed, we still fire "latch.countDown();" , then getFirstToComplete() will pass the "latch.await" after that, then goes to "thorw new InterruptedException", so in hedgedFetchBlockByteRange(), we will continue to try to do getBestNodeDNAddrPair(), and in the test case, the replica is two and due to the previous failed actualGetFromOneDataNode() so one dn had been added into deadnode list:) so it looks like the loop in hedgedFetchBlockByteRange() is:
{code}
while(true) {
getBestNodeDNAddrPair();
getFirstToComplete();
catch exception...
}
{code}

I'll make a patch soon, thank you [~liulei.cn] !

> while loop is executed tens of thousands of times  in Hedged  Read
> ------------------------------------------------------------------
>
>                 Key: HDFS-6591
>                 URL: https://issues.apache.org/jira/browse/HDFS-6591
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs-client
>    Affects Versions: 2.4.0
>            Reporter: LiuLei
>            Assignee: Liang Xie
>         Attachments: LoopTooManyTimesTestCase.patch
>
>
> I download hadoop-2.4.1-rc1 code from http://people.apache.org/~acmurthy/hadoop-2.4.1-rc1/,  I test the  Hedged  Read. I find the while loop in hedgedFetchBlockByteRange method is executed tens of thousands of times.



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