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From "Harsh J (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-554) BlockInfo.ensureCapacity may get a speedup from System.arraycopy()
Date Mon, 21 Nov 2011 14:28:51 GMT

     [ https://issues.apache.org/jira/browse/HDFS-554?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Harsh J updated HDFS-554:
-------------------------

    Attachment: HDFS-554.patch

The difference is apparently very clear, in terms of speed, from even a silly test:

{code}
public class TestSpeed {
  public static void main(String[] args) {
    // Load about a million "Integers".
    Object[] arr = new Object[1000000];
    for (Integer i = 0; i < 1000000; i++) {
      arr[i] = i;
    }
    long now = System.currentTimeMillis();
    // Copy iteratively into a new sized array.
    Object[] arr2 = new Object[3000000];
    for (Integer i = 0; i < arr.length; i++) {
      arr2[i] = arr[i];
    }
    System.out.println(System.currentTimeMillis() - now);
    now = System.currentTimeMillis();
    // arraycopy into a new sized array.
    Object[] arr3 = new Object[3000000];
    System.arraycopy(arr, 0, arr3, 0, arr.length);
    System.out.println(System.currentTimeMillis() - now);
  }
}
{code}

A few runs do, for example:
||Loop||System.arraycopy||
|59|17|
|54|14|
|52|14|
|52|15|
                
> 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
>         Attachments: HDFS-554.patch
>
>
> 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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