@Override
  public void mergeEstimators(NumDistinctValueEstimator o) {
    // Bitwise OR the bitvector with the bitvector in the agg buffer
    for (int i = 0; i < numBitVectors; i++) {
      bitVector[i].or(((FMSketch) o).getBitVector(i));
    }
  }
Resets a distinctValueEstimator object to its original state.
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/common/ndv/fm/FMSketch.java