@Override
  public void setNextNonNullKey(int nonNullKeyPosition) {
    serializedStart = bufferOffset;
    serializedLength = serializedKeyLengths[nonNullKeyPosition];
    Preconditions.checkState(serializedStart + serializedLength <= output.getData().length);
    bufferOffset += serializedLength;
  }
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