Apache Arrow

An implementation of Arrow targeting .NET Standard.

See our current feature matrix for currently available features.

Implementation

• Arrow 0.11 (specification)
• C# 8
• .NET Standard 1.3
• Asynchronous I/O
• Uses modern .NET runtime features such as Span<T>, Memory<T>, MemoryManager<T>, and System.Buffers primitives for memory allocation, memory storage, and fast serialization.
• Uses Acyclic Visitor Pattern for array types and arrays to facilitate serialization, record batch traversal, and format growth.

Known Issues

• Cannot read Arrow files containing tensors.
• Cannot easily modify allocation strategy without implementing a custom memory pool. All allocations are currently 64-byte aligned and padded to 8-bytes.
• Default memory allocation strategy uses an over-allocation strategy with pointer fixing, which results in significant memory overhead for small buffers. A buffer that requires a single byte for storage may be backed by an allocation of up to 64-bytes to satisfy alignment requirements.
• There are currently few builder APIs available for specific array types. Arrays must be built manually with an arrow buffer builder abstraction.
• FlatBuffer code generation is not included in the build process.
• Serialization implementation does not perform exhaustive validation checks during deserialization in every scenario.
• Throws exceptions with vague, inconsistent, or non-localized messages in many situations
• Throws exceptions that are non-specific to the Arrow implementation in some circumstances where it probably should (eg. does not throw ArrowException exceptions)
• Lack of code documentation
• Lack of usage examples

Usage

using System.Diagnostics;
using System.IO;
using System.Threading.Tasks;
using Apache.Arrow;
using Apache.Arrow.Ipc;

public static async Task<RecordBatch> ReadArrowAsync(string filename)
{
    using (var stream = File.OpenRead(filename))
    using (var reader = new ArrowFileReader(stream))
    {
        var recordBatch = await reader.ReadNextRecordBatchAsync();
        Debug.WriteLine("Read record batch with {0} column(s)", recordBatch.ColumnCount);
        return recordBatch;
    }
}

Status

Memory Management

• Allocations are 64-byte aligned and padded to 8-bytes.
• Allocations are automatically garbage collected

Arrays

Primitive Types

• Int8, Int16, Int32, Int64
• UInt8, UInt16, UInt32, UInt64
• Float, Double, Half-float (.NET 6+)
• Binary (variable-length)
• String (utf-8)
• Null

Parametric Types

• Timestamp
• Date32
• Date64
• Decimal
• Time32
• Time64
• Binary (fixed-length)
• List
• Struct

Type Metadata

• Data Types
• Fields
• Schema

Serialization

• File
• Stream

IPC Format

Compression

• Buffer compression is not supported when writing IPC files or streams
• Buffer decompression is supported, but requires installing the Apache.Arrow.Compression package, and passing an Apache.Arrow.Compression.CompressionCodecFactory instance to the ArrowFileReader or ArrowStreamReader constructor. Alternatively, a custom implementation of ICompressionCodecFactory can be used.

Not Implemented

• Serialization
  • Exhaustive validation
  • Dictionary Batch
    • Cannot serialize files or streams containing dictionary batches
  • Dictionary Encoding
• Types
  • Tensor
• Arrays
  • Union
    • Dense
    • Sparse
• Array Operations
  • Equality / Comparison
  • Casting
• Compute
  • There is currently no API available for a compute / kernel abstraction.

Build

Install the latest .NET Core SDK from https://dotnet.microsoft.com/download.

dotnet build

NuGet Build

To build the NuGet package run the following command to build a debug flavor, preview package into the artifacts folder.

dotnet pack

When building the officially released version run: (see Note below about current git repository)

dotnet pack -c Release

Which will build the final/stable package.

NOTE: When building the officially released version, ensure that your git repository has the origin remote set to https://github.com/apache/arrow.git, which will ensure Source Link is set correctly. See https://github.com/dotnet/sourcelink/blob/main/docs/README.md for more information.

There are two output artifacts:

1. Apache.Arrow.<version>.nupkg - this contains the executable assemblies
2. Apache.Arrow.<version>.snupkg - this contains the debug symbols files

Both of these artifacts can then be uploaded to https://www.nuget.org/packages/manage/upload.

Docker Build

Build from the Apache Arrow project root.

docker build -f csharp/build/docker/Dockerfile .

Testing

dotnet test

All build artifacts are placed in the artifacts folder in the project root.

Coding Style

This project follows the coding style specified in Coding Style.

Updating FlatBuffers code

See https://google.github.io/flatbuffers/flatbuffers_guide_use_java_c-sharp.html for how to get the flatc executable.

Run flatc --csharp on each .fbs file in the format folder. And replace the checked in .cs files under FlatBuf with the generated files.

Update the non-generated FlatBuffers .cs files with the files from the google/flatbuffers repo.