protected boolean leftFinishedWithIncIndex() {
    leftIndex++;
    if (leftIndex >= leftBlock.getPositionCount()) {
      resetLeftBlock();
      return true;
    }
    return false;
  }
@return true if current left block is consumed up
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/AbstractMergeSortJoinOperator.java