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https://issues.apache.org/jira/browse/HADOOP-12975?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15278854#comment-15278854
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Colin Patrick McCabe commented on HADOOP-12975:
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Thanks, [~eclark].
{code}
169 // add/subtract the jitter.
170 refreshInterval +=
171 ThreadLocalRandom.current()
172 .nextLong(jitter, jitter);
{code}
Hmm, is this a typo? It seems like this is always going to return exactly
'jitter' since the 'least' and the 'bound' arguments are the same? That seems
to defeat the point of randomization.
https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ThreadLocalRandom.html#nextLong(long,%20long)
{code}
126 if (configuration == null) {
127 return DEFAULT_JITTER;
128 }
{code}
Can we throw an exception in {{GetSpaceUsed#build}} if {{conf == null}}? It's
a weird special case to have no {{Configuration}} object, and I'm not sure why
we'd ever want to do that. Then this function could just be {{return
this.conf.getLong(JITTER_KEY, DEFAULT_JITTER);}}.
> Add jitter to CachingGetSpaceUsed's thread
> ------------------------------------------
>
> Key: HADOOP-12975
> URL: https://issues.apache.org/jira/browse/HADOOP-12975
> Project: Hadoop Common
> Issue Type: Sub-task
> Affects Versions: 2.9.0
> Reporter: Elliott Clark
> Assignee: Elliott Clark
> Attachments: HADOOP-12975v0.patch, HADOOP-12975v1.patch,
> HADOOP-12975v2.patch, HADOOP-12975v3.patch, HADOOP-12975v4.patch,
> HADOOP-12975v5.patch
>
>
> Running DU across lots of disks is very expensive and running all of the
> processes at the same time creates a noticeable IO spike. We should add some
> jitter.
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