Reading and Writing ORC files#

The Apache ORC project provides a standardized open-source columnar storage format for use in data analysis systems. It was created originally for use in Apache Hadoop with systems like Apache Drill, Apache Hive, Apache Impala, and Apache Spark adopting it as a shared standard for high performance data IO.

Apache Arrow is an ideal in-memory representation layer for data that is being read or written with ORC files.

Supported ORC features#

The ORC format has many features, and we support a subset of them.

Data types#

Here are a list of ORC types and mapped Arrow types.

Logical type	Mapped Arrow type	Notes
BOOLEAN	Boolean
BYTE	Int8
SHORT	Int16
INT	Int32
LONG	Int64
FLOAT	Float32
DOUBLE	Float64
STRING	String/LargeString	(2)
BINARY	Binary/LargeBinary/FixedSizeBinary	(2)
TIMESTAMP	Timestamp/Date64	(2) (3)
LIST	List/LargeList/FixedSizeList	(2)
MAP	Map
STRUCT	Struct
UNION	DenseUnion/SparseUnion	(1)
DECIMAL	Decimal128/Decimal64	(2)
DATE	Date32
VARCHAR	String

Unsupported ORC types: CHAR, TIMESTAMP_INSTANT.

(1) We do not support writing UNION types.
(2) On the read side the ORC type is read as the first corresponding Arrow type in the table.
(3) On the read side the ORC TIMESTAMP type is read as the Arrow Timestamp type with arrow::TimeUnit::NANO. Also we currently don’t support timezones.

Compression#

Compression codec
SNAPPY
GZIP/ZLIB
LZ4
ZSTD

Unsupported compression codec: LZO.

Reading ORC Files#

The ORCFileReader class reads data for an entire file or stripe into an ::arrow::Table.

ORCFileReader#

The ORCFileReader class requires a ::arrow::io::RandomAccessFile instance representing the input file.

#include <arrow/adapters/orc/adapter.h>

{
    // ...
    arrow::Status st;
    arrow::MemoryPool* pool = default_memory_pool();
    std::shared_ptr<arrow::io::RandomAccessFile> input = ...;

    // Open ORC file reader
    auto maybe_reader = arrow::adapters::orc::ORCFileReader::Open(input, pool);
    if (!maybe_reader.ok()) {
        // Handle error instantiating file reader...
    }
    std::unique_ptr<arrow::adapters::orc::ORCFileReader> reader = maybe_reader.ValueOrDie();

    // Read entire file as a single Arrow table
    auto maybe_table = reader->Read();
    if (!maybe_table.ok()) {
        // Handle error reading ORC data...
    }
    std::shared_ptr<arrow::Table> table = maybe_table.ValueOrDie();
}

Writing ORC Files#

ORCFileWriter#

An ORC file is written to a OutputStream.

#include <arrow/adapters/orc/adapter.h>
{
    // Oneshot write
    // ...
    std::shared_ptr<arrow::io::OutputStream> output = ...;
    auto writer_options = WriterOptions();
    auto maybe_writer = arrow::adapters::orc::ORCFileWriter::Open(output.get(), writer_options);
    if (!maybe_writer.ok()) {
       // Handle error instantiating file writer...
    }
    std::unique_ptr<arrow::adapters::orc::ORCFileWriter> writer = maybe_writer.ValueOrDie();
    if (!(writer->Write(*input_table)).ok()) {
        // Handle write error...
    }
    if (!(writer->Close()).ok()) {
        // Handle close error...
    }
}

Reading and writing the Arrow IPC format

Reading and writing Parquet files