Apache Arrow DataFusion 8.0.0 Release

Published 16 May 2022
By The Apache Arrow PMC (pmc)

Introduction

DataFusion is an extensible query execution framework, written in Rust, that uses Apache Arrow as its in-memory format.

When you want to extend your Rust project with SQL support, a DataFrame API, or the ability to read and process Parquet, JSON, Avro or CSV data, DataFusion is definitely worth checking out.

DataFusion’s SQL, DataFrame, and manual PlanBuilder API let users access a sophisticated query optimizer and execution engine capable of fast, resource efficient, and parallel execution that takes optimal advantage of today’s multicore hardware. Being written in Rust means DataFusion can offer both the safety of a dynamic language and the resource efficiency of a compiled language.

The Apache Arrow team is pleased to announce the DataFusion 8.0.0 release (and also the release of version 0.7.0 of the Ballista subproject). This covers 3 months of development work and includes 279 commits from the following 49 distinct contributors.

    39  Andy Grove
    33  Andrew Lamb
    21  DuRipeng
    20  Yijie Shen
    19  Yang Jiang
    17  Raphael Taylor-Davies
    11  Dan Harris
    11  Matthew Turner
    11  yahoNanJing
     9  dependabot[bot]
     8  jakevin
     6  Kun Liu
     5  Jiayu Liu
     4  Daniël Heres
     4  mingmwang
     4  xudong.w
     3  Carol (Nichols || Goulding)
     3  Dmitry Patsura
     3  Eduard Karacharov
     3  Jeremy Dyer
     3  Kaushik
     3  Rich
     3  comphead
     3  gaojun2048
     3  Feynman Han
     2  Jie Han
     2  Jon Mease
     2  Tim Van Wassenhove
     2  Yt
     2  Zhang Li
     2  silence-coding
     1  Alexander Spies
     1  George Andronchik
     1  Guillaume Balaine
     1  Hao Xin
     1  Jiacai Liu
     1  Jörn Horstmann
     1  Liang-Chi Hsieh
     1  Max Burke
     1  NaincyKumariKnoldus
     1  Nga Tran
     1  Patrick More
     1  Pierre Zemb
     1  Remzi Yang
     1  Sergey Melnychuk
     1  Stephen Carman
     1  doki

The following sections highlight some of the changes in this release. Of course, many other bug fixes and improvements have been made and we encourage you to check out the changelog for full details.

Summary

DDL Support

DDL support has been expanded to include the following commands for creating databases, schemas, and views. This allows DataFusion to be used more effectively from the CLI.

  • CREATE DATABASE
  • CREATE VIEW
  • CREATE SCHEMA
  • CREATE EXTERNAL TABLE now supports JSON files, IF NOT EXISTS, and partition columns

SQL Support

The SQL query planner now supports a number of new SQL features, including:

  • Subqueries: when used via IN, EXISTS, and as scalars
  • Grouping Sets: CUBE and ROLLUP grouping sets.
  • Aggregate functions: approx_percentile, approx_percentile_cont, approx_percentile_cont_with_weight, approx_distinct, approx_median and array
  • null literals
  • bitwise operations: for example ‘|’

There are also many bug fixes and improvements around normalizing identifiers consistently.

We continue our tradition of incrementally releasing support for new features as they are developed. Thus, while the physical plan may not yet support all new features, it gets more complete each release. These changes also make DataFusion an increasingly compelling choice for projects looking for a SQL parser and query planner that can produce optimized logical plans that can be translated to their own execution engine.

Query Execution & Internals

There are several notable improvements and new features in the query execution engine:

  • The ExecutionContext has been renamed to SessionContext and now supports multi-tenancy
  • The ExecutionPlan trait is no longer async
  • A new serialization API for serializing plans to bytes (based on protobuf)

In addition, we have added several foundational features to drive even more advanced query processing into DataFusion, focusing on running arbitrary queries larger than available memory, and pushing the envelope for performance of sorting, grouping, and joining even further:

Improved file support

DataFusion now supports JSON, both for reading and writing. There are also new DataFrame methods for writing query results to files in CSV, Parquet, and JSON format.

Ballista

Ballista continues to mature and now supports a wider range of operators and expressions. There are also improvements to the scheduler to support UDFs, and there are some robustness improvements, such as cleaning up work directories and persisting session configs to allow schedulers to restart and continue processing in-flight jobs.

Upcoming Work

Here are some of the initiatives that the community plans on working on prior to the next release.

  • There is a proposal to move Ballista to its own top-level arrow-ballista repository to decouple DataFusion and Ballista releases and to allow each project to have documentation better targeted at its particular audience.
  • We plan on increasing the frequency of DataFusion releases, with monthly releases now instead of quarterly. This is driven by requests from the increasing number of projects that now depend on DataFusion.
  • There is ongoing work to implement new optimizer rules to rewrite queries containing subquery expressions as joins, to support a wider range of queries.
  • The new scheduler based on morsel-driven execution will continue to evolve in this next release, with work to refine IO abstractions to improve performance and integration with the new scheduler.
  • Improved performance for Sort, Grouping and Joins

How to Get Involved

If you are interested in contributing to DataFusion, and learning about state-of-the-art query processing, we would love to have you join us on the journey! You can help by trying out DataFusion on some of your own data and projects and let us know how it goes or contribute a PR with documentation, tests or code. A list of open issues suitable for beginners is here

Check out our new Communication Doc on more ways to engage with the community.