[HIVE-21531] Vectorization: all NULL hashcodes are not computed using Murmur3

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 3.1.1, 4.0.0
• Fix Version/s: 4.0.0-alpha-1
• Assignee: Gopal Vijayaraghavan Assign to me
• Reporter: Gopal Vijayaraghavan
• Created: 28/Mar/19 05:53
• Updated: 27/Feb/24 22:23
• Resolved: 24/Apr/19 22:35

Description

The comments in Vectorized hash computation call out the MurmurHash implementation (the one using 0x5bd1e995), while the non-vectorized codepath calls out the Murmur3 one (using 0xcc9e2d51).

The comments here are wrong

 /**
   * Batch compute the hash codes for all the serialized keys.
   *
   * NOTE: MAJOR MAJOR ASSUMPTION:
   *     We assume that HashCodeUtil.murmurHash produces the same result
   *     as MurmurHash.hash with seed = 0 (the method used by ReduceSinkOperator for
   *     UNIFORM distribution).
   */
  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;
    }
  }

but the wrong comment is followed in the Vector RS operator

      System.arraycopy(nullKeyOutput.getData(), 0, nullBytes, 0, nullBytesLength);
      nullKeyHashCode = HashCodeUtil.calculateBytesHashCode(nullBytes, 0, nullBytesLength);