@Override
  protected String getOpImplId() {
    return isLeftSide ? joinOpSpec.getLeftOpId() : joinOpSpec.getRightOpId();
  }
The ID for this {@link PartialJoinOperatorImpl} that includes information about which
side of the join it is for.

@return the {@link PartialJoinOperatorImpl} ID.
samza-core/src/main/java/org/apache/samza/operators/impl/PartialJoinOperatorImpl.java