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https://issues.apache.org/jira/browse/HDFS-3456?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13283090#comment-13283090
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Colin Patrick McCabe commented on HDFS-3456:
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bq. Low bits values should depend on high bits; try max = (1L << 32) + (1L <<
16)
(1L << 32) + (1L << 16) = 4295032832.
I guess I can sort of see what you're getting at here. The (1L << 16) part
will be completely ignored with this current code.
bq. High bits should range from 0 to highMax INCLUSIVELY in some cases; try (1L
<< 32) - 1
(1L << 32) - 1 = 0xffffffff
This is MAX_INT. So you'll take the first branch of the 'if' statement and get
a number between [0 and 0xffffffff).
So, it works fine here.
bq. Two 31-bit int's cannot handle a 63-bit long; try Long.MAX_VALUE
Now this criticism is fair. It could be fixed by just using nextInt() rather
than nextInt(Int.MAX_INT) to get the lower half of the return value.
I think I can fix this code to work in the 64-bit case. The big insight of
this code was that a uniformly randomly distributed 63-bit number can be viewed
as a linear decomposition of several smaller uniformly distributed random
numbers.
I'm tempted to try fixing this. However, it may be more practical to limit
ourselves to 31-bit values...
> 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
>
>
> 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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