Module parquet::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.

use std::{fs, path::Path, rc::Rc};

use parquet::{
    column::{reader::ColumnReader, writer::ColumnWriter},
    file::{
        properties::WriterProperties,
        reader::{FileReader, SerializedFileReader},
        writer::{FileWriter, SerializedFileWriter},
    },
    schema::parser::parse_message_type,
};

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 = Rc::new(parse_message_type(message_type).unwrap());
let props = Rc::new(WriterProperties::builder().build());
let file = fs::File::create(path).unwrap();
let mut writer = SerializedFileWriter::new(file, schema, props).unwrap();
let mut row_group_writer = writer.next_row_group().unwrap();
while let Some(mut col_writer) = row_group_writer.next_column().unwrap() {
    match col_writer {
        // You can also use `get_typed_column_writer` method to extract typed writer.
        ColumnWriter::Int32ColumnWriter(ref mut typed_writer) => {
            typed_writer
                .write_batch(&[1, 2, 3], Some(&[3, 3, 3, 2, 2]), Some(&[0, 1, 0, 1, 1]))
                .unwrap();
        }
        _ => {}
    }
    row_group_writer.close_column(col_writer).unwrap();
}
writer.close_row_group(row_group_writer).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 res = Ok((0, 0));
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) => {
                res = typed_reader.read_batch(
                    8, // batch size
                    Some(&mut def_levels),
                    Some(&mut rep_levels),
                    &mut values,
                );
            }
            _ => {}
        }
    }
}

assert_eq!(res, Ok((3, 5)));
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.