Adam Gutglick
e80694e369
## Which issue does this PR close? - Closes #20134 . ## Rationale for this change The check for simplifying const expressions was recursive and expensive, repeatedly checking the expression's children in a recursive way. I've tried other approached like pre-computing the result for all expressions outside of the loop and using that cache during the traversal, but I've found that it only yielded between 5-8% improvement while adding complexity, while this approach simplifies the code and seems to be more performant in my benchmarks (change is compared to current main branch): ``` tpc-ds/q76/cs/16 time: [27.112 µs 27.159 µs 27.214 µs] change: [−13.533% −13.167% −12.801%] (p = 0.00 < 0.05) Performance has improved. Found 7 outliers among 100 measurements (7.00%) 1 (1.00%) low mild 4 (4.00%) high mild 2 (2.00%) high severe tpc-ds/q76/ws/16 time: [26.175 µs 26.280 µs 26.394 µs] change: [−14.312% −13.833% −13.346%] (p = 0.00 < 0.05) Performance has improved. Found 1 outliers among 100 measurements (1.00%) 1 (1.00%) low mild tpc-ds/q76/cs/128 time: [195.79 µs 196.17 µs 196.56 µs] change: [−14.362% −14.080% −13.816%] (p = 0.00 < 0.05) Performance has improved. Found 5 outliers among 100 measurements (5.00%) 1 (1.00%) low severe 1 (1.00%) low mild 3 (3.00%) high mild tpc-ds/q76/ws/128 time: [197.08 µs 197.61 µs 198.23 µs] change: [−13.531% −13.142% −12.737%] (p = 0.00 < 0.05) Performance has improved. Found 3 outliers among 100 measurements (3.00%) 1 (1.00%) low mild 2 (2.00%) high mild ``` ## What changes are included in this PR? 1. `simplify_const_expr` now only checks itself and whether all of its children are literals, because it assumes the order of simplification is bottoms-up. 2. Removes some code from the public API, see the last section for the full details. ## Are these changes tested? Existing test suite ## Are there any user-facing changes? I suggest removing some of the physical expression simplification code from the public API, which I believe reduces the maintenance burden here. These changes also helps removing code like the distinct `simplify_const_expr` and `simplify_const_expr_with_dummy`. 1. Makes all `datafusion-physical-expr::simplifier` sub-modules (`not` and `const_evaluator`) private, including their key functions. They are not used externally, and being able to change their behavior seems more valuable long term. The simplifier is also not currently an extension point as far as I can tell, so there's no value in providing atomic building blocks like them for now. 2. Removes `has_column_references` completely, its trivial to re-implement and isn't used anywhere in the codebase. --------- Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>
Apache DataFusion
DataFusion is an extensible query engine written in Rust that uses Apache Arrow as its in-memory format.
This crate provides libraries and binaries for developers building fast and feature-rich database and analytic systems, customized for particular workloads. See use cases for examples. The following related subprojects target end users:
- DataFusion Python offers a Python interface for SQL and DataFrame queries.
- DataFusion Comet is an accelerator for Apache Spark based on DataFusion.
"Out of the box," DataFusion offers SQL and DataFrame APIs, excellent performance, built-in support for CSV, Parquet, JSON, and Avro, extensive customization, and a great community.
DataFusion features a full query planner, a columnar, streaming, multi-threaded, vectorized execution engine, and partitioned data sources. You can customize DataFusion at almost all points including additional data sources, query languages, functions, custom operators and more. See the Architecture section for more details.
Here are links to important resources:
- Project Site
- Installation
- Rust Getting Started
- Rust DataFrame API
- Rust API docs
- Rust Examples
- Python DataFrame API
- Architecture
What can you do with this crate?
DataFusion is great for building projects such as domain-specific query engines, new database platforms and data pipelines, query languages and more. It lets you start quickly from a fully working engine, and then customize those features specific to your needs. See the list of known users.
Contributing to DataFusion
Please see the contributor guide and communication pages for more information.
Crate features
This crate has several features which can be specified in your Cargo.toml.
Default features:
nested_expressions: functions for working with nested types such asarray_to_stringcompression: reading files compressed withxz2,bzip2,flate2, andzstdcrypto_expressions: cryptographic functions such asmd5andsha256datetime_expressions: date and time functions such asto_timestampencoding_expressions:encodeanddecodefunctionsparquet: support for reading the Apache Parquet formatsql: support for SQL parsing and planningregex_expressions: regular expression functions, such asregexp_matchunicode_expressions: include Unicode-aware functions such ascharacter_lengthunparser: enables support to reverse LogicalPlans back into SQLrecursive_protection: uses recursive for stack overflow protection.
Optional features:
avro: support for reading the Apache Avro formatbacktrace: include backtrace information in error messagesparquet_encryption: support for using Parquet Modular Encryptionserde: enable arrow-schema'sserdefeature
DataFusion API Evolution and Deprecation Guidelines
Public methods in Apache DataFusion evolve over time: while we try to maintain a stable API, we also improve the API over time. As a result, we typically deprecate methods before removing them, according to the deprecation guidelines.
Dependencies and Cargo.lock
Following the guidance on committing Cargo.lock files, this project commits
its Cargo.lock file.
CI uses the committed Cargo.lock file, and dependencies are updated regularly
using Dependabot PRs.