Skip to content

orc.rst

Latest commit

 

History

History
183 lines (147 loc) · 6.71 KB

orc.rst

File metadata and controls

183 lines (147 loc) · 6.71 KB
.. default-domain:: cpp
.. cpp:namespace:: arrow::adapters::orc

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.

.. seealso::
   :ref:`ORC reader/writer API reference <cpp-api-orc>`.

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 :cpp:enumerator:`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 :class:`ORCFileReader` class reads data for an entire file or stripe into an :class:`::arrow::Table`.

ORCFileReader

The :class:`ORCFileReader` class requires a :class:`::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 :class:`~arrow::io::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...
    }
}