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https://issues.apache.org/jira/browse/HDFS-3456?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13286118#comment-13286118
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Andy Isaacson commented on HDFS-3456:
-------------------------------------
.003.patch uses nextDouble, which does not provide enough entropy -- there are
only 53 bits in the mantissa of a double. So if I ask for 60-bit random
values, it will return a 60-bit value with 7 zero bits at the bottom. (Or
something like that -- I didn't test the specific failure mode.)
I am not aware of any easy way to implement nextRandomLong given only a 31-bit
nextInt. So, I would suggest to address the potential overflow in
scheduleBlockReport -- either use nextDouble directly, or limit the maximum
range to Integer.MAX_VALUE.
> blockReportInterval is long value but when we take the random value it uses
> getRandom().nextInt,it is causing frequently BR
> ---------------------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-3456
> URL: https://issues.apache.org/jira/browse/HDFS-3456
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: data-node
> Affects Versions: 2.0.0-alpha
> Reporter: Brahma Reddy Battula
> Assignee: Colin Patrick McCabe
> Priority: Minor
> Attachments: HDFS-3456.001.patch, HDFS-3456.002.patch,
> HDFS-3456.003.patch
>
>
> blockReportInterval is long value but when we take the random value it uses
> getRandom().nextInt.
> Due to this, offerService can throw exception as long may get rotated to
> negative value.
> So, block report may send very frequently.
> {code}
> if (resetBlockReportTime) {
> lastBlockReport = startTime -
> DFSUtil.getRandom().nextInt((int)(dnConf.blockReportInterval));
> resetBlockReportTime = false;
> {code}
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