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https://issues.apache.org/jira/browse/HDFS-13978?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16650328#comment-16650328
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BELUGA BEHR commented on HDFS-13978:
------------------------------------
All the failed unit tests are known flaky tests. Please consider the patch for
inclusion into the project.
> Review of DiskBalancer
> ----------------------
>
> Key: HDFS-13978
> URL: https://issues.apache.org/jira/browse/HDFS-13978
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode, hdfs
> Affects Versions: 3.2.0
> Reporter: BELUGA BEHR
> Assignee: BELUGA BEHR
> Priority: Minor
> Attachments: HDFS-13978.1.patch
>
>
> * Use ArrayList instead of LinkedList. Especially because this code here uses
> the {{List#get()}} method, which is very slow for the LinkedList since it has
> to traverse every node to get to the offset: O(N^2)
> {code}
> ExtendedBlock getNextBlock(List<FsVolumeSpi.BlockIterator> poolIters,
> DiskBalancerWorkItem item) {
> Preconditions.checkNotNull(poolIters);
> int currentCount = 0;
> ExtendedBlock block = null;
> while (block == null && currentCount < poolIters.size()) {
> currentCount++;
> int index = poolIndex++ % poolIters.size();
> FsVolumeSpi.BlockIterator currentPoolIter = poolIters.get(index);
> block = getBlockToCopy(currentPoolIter, item);
> }
> {code}
> * Do not "log and throw" errors. This is an anti-pattern and should be
> avoided. Log or throw, but don't do both. Removed some logging
> * Improved other logging statements
> * Improved the {{hashcode}} method of one of the inner classes. It was
> instantiating a List and performing iteration for every call. Replace with
> Eclipse-generated hashcode method.
> * Fixed compiler warnings for deprecated code or code that was not
> parameterized
> * Fix check style issue
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