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https://issues.apache.org/jira/browse/HDFS-15574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17195661#comment-17195661
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Mingliang Liu commented on HDFS-15574:
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V3 patch looks good to me. Thanks,

> Remove unnecessary sort of block list in DirectoryScanner
> ---------------------------------------------------------
>
>                 Key: HDFS-15574
>                 URL: https://issues.apache.org/jira/browse/HDFS-15574
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 3.4.0
>            Reporter: Stephen O'Donnell
>            Assignee: Stephen O'Donnell
>            Priority: Major
>         Attachments: HDFS-15574.001.patch, HDFS-15574.002.patch, 
> HDFS-15574.003.patch
>
>
> These lines of code in DirectoryScanner#scan(), obtain a snapshot of the 
> finalized blocks from memory, and then sort them, under the DN lock. However 
> the blocks are stored in a sorted structure (FoldedTreeSet) and hence the 
> sort should be unnecessary.
> {code}
>   final List<ReplicaInfo> bl = dataset.getFinalizedBlocks(bpid);
>   Collections.sort(bl); // Sort based on blockId
> {code}
> This Jira removes the sort, and renames the getFinalizedBlocks to 
> getSortedFinalizedBlocks to make the intent of the method more clear.
> Also added a test, just in case the underlying block structure is ever 
> changed to something unsorted.



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