[jira] [Resolved] (SPARK-22838) Avoid unnecessary copying of data

["Saisai Shao (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-22838?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Saisai Shao resolved SPARK-22838.
---------------------------------
    Resolution: Invalid

> Avoid unnecessary copying of data
> ---------------------------------
>
>                 Key: SPARK-22838
>                 URL: https://issues.apache.org/jira/browse/SPARK-22838
>             Project: Spark
>          Issue Type: Improvement
>          Components: Spark Core
>    Affects Versions: 2.2.1
>            Reporter: Xianyang Liu
>            Priority: Major
>
> If we read data from FileChannel to HeapByteBuffer, there is a need to copy the data from the off-heap to the on-heap, you can see the follow code:
> ```java
> static int read(FileDescriptor var0, ByteBuffer var1, long var2, NativeDispatcher var4) throws IOException {
>     if(var1.isReadOnly()) {
>       throw new IllegalArgumentException("Read-only buffer");
>     } else if(var1 instanceof DirectBuffer) {
>       return readIntoNativeBuffer(var0, var1, var2, var4);
>     } else {
>       ByteBuffer var5 = Util.getTemporaryDirectBuffer(var1.remaining());
>       int var7;
>       try {
>         int var6 = readIntoNativeBuffer(var0, var5, var2, var4);
>         var5.flip();
>         if(var6 > 0) {
>           var1.put(var5);
>         }
>         var7 = var6;
>       } finally {
>         Util.offerFirstTemporaryDirectBuffer(var5);
>       }
>       return var7;
>     }
>   }
> ```



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