Module column

Low level column reader and writer APIs.

This API is designed for reading and writing column values, definition and repetition levels directly.

Example of writing and reading data

Data has the following format:

+---------------+
|         values|
+---------------+
|[1, 2]         |
|[3, null, null]|
+---------------+

The example uses column writer and reader APIs to write raw values, definition and repetition levels and read them to verify write/read correctness.

let path = Path::new("/path/to/column_sample.parquet");

// Writing data using column writer API.

let message_type = "
  message schema {
    optional group values (LIST) {
      repeated group list {
        optional INT32 element;
      }
    }
  }
";
let schema = Arc::new(parse_message_type(message_type).unwrap());
let file = fs::File::create(path).unwrap();
let mut writer = SerializedFileWriter::new(file, schema, Default::default()).unwrap();

let mut row_group_writer = writer.next_row_group().unwrap();
while let Some(mut col_writer) = row_group_writer.next_column().unwrap() {
    col_writer
        .typed::<Int32Type>()
        .write_batch(&[1, 2, 3], Some(&[3, 3, 3, 2, 2]), Some(&[0, 1, 0, 1, 1]))
        .unwrap();
    col_writer.close().unwrap();
}
row_group_writer.close().unwrap();

writer.close().unwrap();

// Reading data using column reader API.

let file = fs::File::open(path).unwrap();
let reader = SerializedFileReader::new(file).unwrap();
let metadata = reader.metadata();

let mut values = vec![0; 8];
let mut def_levels = vec![0; 8];
let mut rep_levels = vec![0; 8];

for i in 0..metadata.num_row_groups() {
    let row_group_reader = reader.get_row_group(i).unwrap();
    let row_group_metadata = metadata.row_group(i);

    for j in 0..row_group_metadata.num_columns() {
        let mut column_reader = row_group_reader.get_column_reader(j).unwrap();
        match column_reader {
            // You can also use `get_typed_column_reader` method to extract typed reader.
            ColumnReader::Int32ColumnReader(ref mut typed_reader) => {
                let (records, values, levels) = typed_reader.read_records(
                    8, // maximum records to read
                    Some(&mut def_levels),
                    Some(&mut rep_levels),
                    &mut values,
                ).unwrap();
                assert_eq!(records, 2);
                assert_eq!(levels, 5);
                assert_eq!(values, 3);
            }
            _ => {}
        }
    }
}

assert_eq!(values, vec![1, 2, 3, 0, 0, 0, 0, 0]);
assert_eq!(def_levels, vec![3, 3, 3, 2, 2, 0, 0, 0]);
assert_eq!(rep_levels, vec![0, 1, 0, 1, 1, 0, 0, 0]);

Modules

• page
  Contains Parquet Page definitions and page reader interface.
• reader
  Contains column reader API.
• writer
  Contains column writer API.