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https://issues.apache.org/jira/browse/HDFS-767?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ning Zhang updated HDFS-767:
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Attachment: HDFS-767_2.patch
I am attaching the second version of the patch. It fixes the javac warning
issue.
I also did a simple test on nanoTime() on jdk1.6.0_16 on Linux and found it is
highly fine grained (consistent with the description that it was implemented
using CPU clock cycles). So Random() seed confliction is fairly rare. As
mentioined by Dhruba, Random() was used in many places. So we probably don't
want to change it in this one place. A separate JIRA is probably the best if
it renders iteself as a real problem later.
> 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
> Attachments: HDFS-767.patch, HDFS-767_2.patch
>
>
> 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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