Revert "[FLINK-4154] [core] Correction of murmur hash breaks backward…

…s compatibility"

This reverts commit 81cf229.

We had an incorrent implementation of Murmur hash in Flink 1.0. This
was fixed in 641a0d4 for Flink 1.1. Then we thought that we need to
revert this in order to ensure backwards compatability between Flink
1.0 and 1.1 savepoints (81cf22). Turns out, savepoint backwards
compatability is broken for other reasons, too. Therefore, we revert
81cf22 here, ending up with a correct implementation of Murmur hash
again.

flink-contrib/flink-storm-examples/src/test/java/org/apache/flink/storm/tests/StormFieldsGroupingITCase.java

@@ -49,9 +49,9 @@ protected void preSubmit() throws Exception {
 
  @Override
  protected void postSubmit() throws Exception {
- compareResultsByLinesInMemory("3> -1155484576\n" + "3> 1033096058\n" + "3> -1930858313\n" +
- "3> 1431162155\n" + "4> -1557280266\n" + "4> -1728529858\n" + "4> 1654374947\n" +
- "4> -65105105\n" + "4> -518907128\n" + "4> -252332814\n", this.resultPath);
+ compareResultsByLinesInMemory("4> -1155484576\n" + "3> 1033096058\n" + "3> -1930858313\n" +
+ "4> 1431162155\n" + "3> -1557280266\n" + "4> -1728529858\n" + "3> 1654374947\n" +
+ "3> -65105105\n" + "3> -518907128\n" + "4> -252332814\n", this.resultPath);
  }
 
  @Override

flink-core/src/main/java/org/apache/flink/util/MathUtils.java

@@ -135,10 +135,7 @@ public static int murmurHash(int code) {
  code *= 0x1b873593;
 
  code = Integer.rotateLeft(code, 13);
- // By the MurmurHash algorithm the following should be "code = code * 5 + 0xe6546b64;" (see FLINK-3623)
- // but correcting the algorithm is a breaking change (see FLINK-4154). The effect of the resulting skew
- // increases with increased parallelism (see FLINK-4154).
- code *= 0xe6546b64;
+ code = code * 5 + 0xe6546b64;
 
  code ^= 4;
  code ^= code >>> 16;

flink-streaming-scala/src/test/scala/org/apache/flink/streaming/api/scala/StreamingOperatorsITCase.scala

@@ -74,7 +74,8 @@ class StreamingOperatorsITCase extends ScalaStreamingMultipleProgramsTestBase {
 
  override def run(ctx: SourceContext[(Int, Int)]): Unit = {
  0 until numElements foreach {
- i => ctx.collect((MathUtils.murmurHash(i) % numKeys, i))
+ // keys '1' and '2' hash to different buckets
+ i => ctx.collect((1 + (MathUtils.murmurHash(i)) % numKeys, i))
  }
  }
 

flink-tests/src/test/java/org/apache/flink/test/streaming/api/StreamingOperatorsITCase.java

@@ -223,7 +223,8 @@ public TupleSource(int numElements, int numKeys) {
  @Override
  public void run(SourceContext<Tuple2<Integer, Integer>> ctx) throws Exception {
  for (int i = 0; i < numElements; i++) {
- Tuple2<Integer, Integer> result = new Tuple2<>(MathUtils.murmurHash(i) % numKeys, i);
+ // keys '1' and '2' hash to different buckets
+ Tuple2<Integer, Integer> result = new Tuple2<>(1 + (MathUtils.murmurHash(i) % numKeys), i);
  ctx.collect(result);
  }
  }