2 files changed, 20 insertions, 0 deletions
diff --git a/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java b/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
index 3e1cc67dbf..57522003ba 100644
--- a/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
+++ b/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
@@ -138,6 +138,15 @@ public final class UTF8String implements Comparable<UTF8String>, Serializable {
   }
 
   /**
+   * Returns a 64-bit integer that can be used as the prefix used in sorting.
+   */
+  public long getPrefix() {
+    long p = PlatformDependent.UNSAFE.getLong(base, offset);
+    p = java.lang.Long.reverseBytes(p);
+    return p;
+  }
+
+  /**
    * Returns the underline bytes, will be a copy of it if it's part of another array.
    */
   public byte[] getBytes() {
diff --git a/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java b/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java
index e2a5628ff4..42e09e435a 100644
--- a/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java
+++ b/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java
@@ -64,7 +64,18 @@ public class UTF8StringSuite {
   }
 
   @Test
+  public void prefix() {
+    assertTrue(fromString("a").getPrefix() - fromString("b").getPrefix() < 0);
+    assertTrue(fromString("ab").getPrefix() - fromString("b").getPrefix() < 0);
+    assertTrue(
+      fromString("abbbbbbbbbbbasdf").getPrefix() - fromString("bbbbbbbbbbbbasdf").getPrefix() < 0);
+    assertTrue(fromString("").getPrefix() - fromString("a").getPrefix() < 0);
+    assertTrue(fromString("你好").getPrefix() - fromString("世界").getPrefix() > 0);
+  }
+
+  @Test
   public void compareTo() {
+    assertTrue(fromString("").compareTo(fromString("a")) < 0);
     assertTrue(fromString("abc").compareTo(fromString("ABC")) > 0);
     assertTrue(fromString("abc0").compareTo(fromString("abc")) > 0);
     assertTrue(fromString("abcabcabc").compareTo(fromString("abcabcabc")) == 0);