Cross-language compatibility is important in Apache Arrow. To maintain it, we use the following process when dealing with changes to the format (files in https://github.com/apache/arrow/tree/main/format):

• We must discuss and vote on the changes on the public mailing list
• We must have at least two reference implementations and associated integration tests

These do not have to be done in order. In most cases, having at least one draft reference implementation is helpful for design discussion.

Changes to the format should be discussed on the public mailing list. Anyone can join the discussion. The discussion should be started by a thread in dev@arrow.apache.org with the [DISCUSS] prefixed subject.

Here are some examples:

• [Discuss][Format] Add 32-bit and 64-bit Decimals
• [DISCUSS][Format] Starting to do some concrete work on the new "StringView" columnar data type

The voting process is used to verify we have reached consensus. We can start a vote for the format changes after we reach consensus in the preceding DISCUSS mailing list thread. Similar to discussion threads, voting thread must have the subject prefix [VOTE].

See also: Apache Voting Process

We must have at least two reference implementations and associated integration tests to confirm whether the format changes are compatible across languages and consistent.

Reference implementations must be within complete Arrow implementations. For example, the C++ library is acceptable but the Python library is not, since it is a wrapper around the C++ library. Here are candidate implementations:

• The C++ implementation
• The Java implementation
• The Rust (arrow-rs) implementation
• The Go implementation

We can discuss and vote to add more implementations to the list. We may use :doc:`../status` to determine which implementations are complete.

The format version (which is separate from the library versions) must also be incremented as new changed are made. See :doc:`Versioning`.