HBASE-12716 A bug in RegionSplitter.UniformSplit algorithm (Weichen Ye)

hbase-common/src/main/java/org/apache/hadoop/hbase/util/Bytes.java

@@ -1701,8 +1701,19 @@ public class Bytes {
       diffBI = diffBI.add(BigInteger.ONE);
     }
     final BigInteger splitsBI = BigInteger.valueOf(num + 1);
+    //when diffBI < splitBI, use an additional byte to increase diffBI
     if(diffBI.compareTo(splitsBI) < 0) {
-      return null;
+      byte[] aPaddedAdditional = new byte[aPadded.length+1];
+      byte[] bPaddedAdditional = new byte[bPadded.length+1];
+      for (int i = 0; i < aPadded.length; i++){
+        aPaddedAdditional[i] = aPadded[i];
+      }
+      for (int j = 0; j < bPadded.length; j++){
+        bPaddedAdditional[j] = bPadded[j];
+      }
+      aPaddedAdditional[aPadded.length] = 0;
+      bPaddedAdditional[bPadded.length] = 0;
+      return iterateOnSplits(aPaddedAdditional, bPaddedAdditional, inclusive,  num);
     }
     final BigInteger intervalBI;
     try {

hbase-common/src/test/java/org/apache/hadoop/hbase/util/TestBytes.java

@@ -101,9 +101,10 @@ public class TestBytes extends TestCase {
     }
     assertTrue("Returned split should have 3 parts but has " + parts.length, parts.length == 3);
 
-    // If split more than once, this should fail
+    // If split more than once, use additional byte to split
     parts = Bytes.split(low, high, 2);
-    assertTrue("Returned split but should have failed", parts == null);
+    assertTrue("Split with an additional byte", parts != null);
+    assertEquals(parts.length, low.length + 1);
 
     // Split 0 times should throw IAE
     try {

hbase-server/src/test/java/org/apache/hadoop/hbase/util/TestRegionSplitter.java

@@ -207,6 +207,9 @@ public class TestRegionSplitter {
                 xFF, xFF, xFF}, lastRow);
         assertArrayEquals(splitPoint,
                 new byte[] {(byte)0xef, xFF, xFF, xFF, xFF, xFF, xFF, xFF});
+
+        splitPoint = splitter.split(new byte[] {'a', 'a', 'a'}, new byte[] {'a', 'a', 'b'});
+        assertArrayEquals(splitPoint, new byte[] {'a', 'a', 'a', (byte)0x80 });
     }
 
   @Test
@@ -227,7 +230,7 @@ public class TestRegionSplitter {
     assertTrue(splitFailsPrecondition(algo, "\\xAA", "\\xAA")); // range error
     assertFalse(splitFailsPrecondition(algo, "\\x00", "\\x02", 3)); // should be fine
     assertFalse(splitFailsPrecondition(algo, "\\x00", "\\x0A", 11)); // should be fine
-    assertTrue(splitFailsPrecondition(algo, "\\x00", "\\x0A", 12)); // too granular
+    assertFalse(splitFailsPrecondition(algo, "\\x00", "\\x0A", 12)); // should be fine
   }
 
   private boolean splitFailsPrecondition(SplitAlgorithm algo) {