protected void computeSerializedHashCodes() {
    int offset = 0;
    int keyLength;
    byte[] bytes = output.getData();
    for (int i = 0; i < nonNullKeyCount; i++) {
      keyLength = serializedKeyLengths[i];
      hashCodes[i] = Murmur3.hash32(bytes, offset, keyLength, 0);
      offset += keyLength;
    }
  }
Batch compute the hash codes for all the serialized keys.

NOTE: MAJOR MAJOR ASSUMPTION:
    We use Murmur3.hash32(seed=0) across the board for the ReduceSink UNIFORM distribution.
    Previous use of HashCodeUtil is deprecated.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/keyseries/VectorKeySeriesSerializedImpl.java