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feat: Add compatibility guide #316

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Apr 24, 2024
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feat: Add compatibility guide #316

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40 changes: 40 additions & 0 deletions docs/source/compatibility.md
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<!---
Licensed to the Apache Software Foundation (ASF) under one
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regarding copyright ownership. The ASF licenses this file
to you under the Apache License, Version 2.0 (the
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Unless required by applicable law or agreed to in writing,
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-->

# Compatibility Guide

Comet aims to provide consistent results with the version of Apache Spark that is being used.

This guide offers information about areas of functionality where there are known differences.

## ANSI mode

Comet currently ignores ANSI mode in most cases, and therefore can produce different results than Spark. By default,
Comet will fall back to Spark if ANSI mode is enabled. To enable Comet to accelerate queries when ANSI mode is enabled,
specify `spark.comet.ansi.enabled=true` in the Spark configuration. Comet's ANSI support is experimental and should not
be used in production.

There is an [epic](https://github.com/apache/datafusion-comet/issues/313) where we are tracking the work to fully implement ANSI support.

## Cast

Comet currently delegates to Apache DataFusion for most cast operations, and this means that the behavior is not
guaranteed to be consistent with Spark.

There is an [epic](https://github.com/apache/datafusion-comet/issues/286) where we are tracking the work to implement Spark-compatible cast expressions.
1 change: 1 addition & 0 deletions docs/source/index.rst
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Expand Up @@ -43,6 +43,7 @@ GitHub repository at https://github.com/apache/datafusion-comet.
:maxdepth: 1
:caption: Project Links

compatibility
Github and Issue Tracker <https://github.com/apache/datafusion-comet>

.. _toc.asf-links:
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