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https://issues.apache.org/jira/browse/HDFS-767?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12797439#action_12797439
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Hudson commented on HDFS-767:
-----------------------------
Integrated in Hdfs-Patch-h5.grid.sp2.yahoo.net #171 (See
[http://hudson.zones.apache.org/hudson/job/Hdfs-Patch-h5.grid.sp2.yahoo.net/171/])
> Job failure due to BlockMissingException
> ----------------------------------------
>
> Key: HDFS-767
> URL: https://issues.apache.org/jira/browse/HDFS-767
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Ning Zhang
> Assignee: Ning Zhang
> Fix For: 0.22.0
>
> Attachments: HDFS-767.patch, HDFS-767_2.patch, HDFS-767_3.patch,
> HDFS-767_4.txt
>
>
> If a block is request by too many mappers/reducers (say, 3000) at the same
> time, a BlockMissingException is thrown because it exceeds the upper limit (I
> think 256 by default) of number of threads accessing the same block at the
> same time. The DFSClient wil catch that exception and retry 3 times after
> waiting for 3 seconds. Since the wait time is a fixed value, a lot of clients
> will retry at about the same time and a large portion of them get another
> failure. After 3 retries, there are about 256*4 = 1024 clients got the block.
> If the number of clients are more than that, the job will fail.
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