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From "Liang Xie (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6695) Investigate using Java 7's nonblocking file I/O in BlockReaderLocal to implement read timeouts
Date Thu, 17 Jul 2014 04:00:06 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6695?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14064550#comment-14064550
] 

Liang Xie commented on HDFS-6695:
---------------------------------

I did not look through AsynchronousfileChannel impl, but per the above link saying: " This
class also defines read and write methods that initiate asynchronous operations, returning
a Future to represent the pending result of the operation. The Future may be used to check
if the operation has completed, wait for its completion, and retrieve the result. ",  seems
does the same idea like my pseudo code at https://issues.apache.org/jira/browse/HDFS-6286?focusedCommentId=14008621&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14008621

> Investigate using Java 7's nonblocking file I/O in BlockReaderLocal to implement read
timeouts
> ----------------------------------------------------------------------------------------------
>
>                 Key: HDFS-6695
>                 URL: https://issues.apache.org/jira/browse/HDFS-6695
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Colin Patrick McCabe
>
> In BlockReaderLocal, the "read" system call could block for a long time if the disk drive
is having problems, or there is a huge amount of I/O contention.  This might cause poor latency
performance.
> In the remote block readers, we have implemented a read timeout, but we don't have one
for the local block reader, since {{FileChannel#read}} doesn't support this.  
> Once we move to JDK 7, we should investigate the {{java.nio.file}} nonblocking file I/O
package to see if it could be used to implement read timeouts.



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