@Override
  public long ramBytesUsed() {
    return INSTANCE_SIZE
        + MemoryEstimationHelper.getEstimatedSizeOfAccountableObject(leftChild)
        + MemoryEstimationHelper.getEstimatedSizeOfAccountableObject(rightChild)
        + RamUsageEstimator.sizeOf(leftOutputSymbolIdx)
        + RamUsageEstimator.sizeOf(rightOutputSymbolIdx)
        + MemoryEstimationHelper.getEstimatedSizeOfAccountableObject(operatorContext)
        + resultBuilder.getRetainedSizeInBytes();
  }
This method will be invoked only when `allRightLessThanLeft` or `leftFinished`.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/MergeSortFullOuterJoinOperator.java