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https://issues.apache.org/jira/browse/HDFS-554?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12748603#action_12748603
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Suresh Srinivas commented on HDFS-554:
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Also the array size that we are copying is generally 9 (assuming 3 replicas)

> BlockInfo.ensureCapacity may get a speedup from System.arraycopy()
> ------------------------------------------------------------------
>
>                 Key: HDFS-554
>                 URL: https://issues.apache.org/jira/browse/HDFS-554
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>    Affects Versions: 0.21.0
>            Reporter: Steve Loughran
>            Priority: Minor
>
> BlockInfo.ensureCapacity() uses a for() loop to copy the old array data into 
> the expanded array.  {{System.arraycopy()}} is generally much faster for 
> this, as it can do a bulk memory copy. There is also the typesafe Java6 
> {{Arrays.copyOf()}} to consider, though here it offers no tangible benefit.

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