reduce bytearray copy to minimal optimize VSizeIndexedWriter

processing/src/main/java/io/druid/segment/data/VSizeIndexedInts.java

@@ -50,11 +50,31 @@ public class VSizeIndexedInts implements IndexedInts, Comparable<VSizeIndexedInt
     return fromList(Lists.<Integer>newArrayList(), 0);
   }
 
+  /**
+   * provide for performance reason.
+   */
+  public static byte[] getBytesNoPaddingfromList(List<Integer> list, int maxValue)
+  {
+    int numBytes = getNumBytesForMax(maxValue);
+
+    final ByteBuffer buffer = ByteBuffer.allocate((list.size() * numBytes));
+    writeToBuffer(buffer, list, numBytes, maxValue);
+
+    return buffer.array();
+  }
+
   public static VSizeIndexedInts fromList(List<Integer> list, int maxValue)
   {
     int numBytes = getNumBytesForMax(maxValue);
 
     final ByteBuffer buffer = ByteBuffer.allocate((list.size() * numBytes) + (4 - numBytes));
+    writeToBuffer(buffer, list, numBytes, maxValue);
+
+    return new VSizeIndexedInts(buffer.asReadOnlyBuffer(), numBytes);
+  }
+
+  private static void writeToBuffer(ByteBuffer buffer, List<Integer> list, int numBytes, int maxValue)
+  {
     int i = 0;
     for (Integer val : list) {
       if (val < 0) {
@@ -69,8 +89,6 @@ public class VSizeIndexedInts implements IndexedInts, Comparable<VSizeIndexedInt
       ++i;
     }
     buffer.position(0);
-
-    return new VSizeIndexedInts(buffer.asReadOnlyBuffer(), numBytes);
   }
 
   public static byte getNumBytesForMax(int maxValue)

processing/src/main/java/io/druid/segment/data/VSizeIndexedWriter.java

@@ -70,7 +70,7 @@ public class VSizeIndexedWriter implements Closeable
 
   public void write(List<Integer> ints) throws IOException
   {
-    byte[] bytesToWrite = ints == null ? EMPTY_ARRAY : VSizeIndexedInts.fromList(ints, maxId).getBytesNoPadding();
+    byte[] bytesToWrite = ints == null ? EMPTY_ARRAY : VSizeIndexedInts.getBytesNoPaddingfromList(ints, maxId);
 
     valuesOut.write(bytesToWrite);
 

processing/src/test/java/io/druid/segment/data/VSizeIndexedIntsTest.java

@@ -22,9 +22,12 @@ package io.druid.segment.data;
 import org.junit.Assert;
 import org.junit.Test;
 
+import com.google.common.primitives.Ints;
+
 import java.io.ByteArrayOutputStream;
 import java.nio.ByteBuffer;
 import java.nio.channels.Channels;
+import java.util.List;
 
 /**
  */
@@ -63,4 +66,15 @@ public class VSizeIndexedIntsTest
     }
   }
 
+  @Test
+  public void testGetBytesNoPaddingfromList() throws Exception
+  {
+    final int[] array = {1, 2, 4, 5, 6, 8, 9, 10};
+    List<Integer> list = Ints.asList(array);
+    int maxValue = Ints.max(array);
+    VSizeIndexedInts ints = VSizeIndexedInts.fromList(list, maxValue);
+    byte[] bytes1 = ints.getBytesNoPadding();
+    byte[] bytes2 = VSizeIndexedInts.getBytesNoPaddingfromList(list, maxValue);
+    Assert.assertArrayEquals(bytes1, bytes2);
+  }
 }