presto-orc/src/main/java/io/prestosql/orc/reader/StructColumnReader.java/StructColumnReader/getRetainedSizeInBytes
class StructColumnReader:    @Override
    public long getRetainedSizeInBytes()
    {
        long retainedSizeInBytes = INSTANCE_SIZE;
        for (ColumnReader structField : structFields.values()) {
            retainedSizeInBytes += structField.getRetainedSizeInBytes();
        }
        return retainedSizeInBytes;
    }