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### What changes were proposed in this pull request? This PR fixes an existing correctness issue where a non-deterministic With-CTE can be executed multiple times producing different results, by deferring the inline of With-CTE to after the analysis stage. This fix also provides the future opportunity of performance improvement by executing deterministic With-CTEs only once in some circumstances. The major changes include: 1. Added new With-CTE logical nodes: `CTERelationDef`, `CTERelationRef`, `WithCTE`. Each `CTERelationDef` has a unique ID and the mapping between CTE def and CTE ref is based on IDs rather than names. `WithCTE` is a resolved version of `With`, only that: 1) `WithCTE` is a multi-children logical node so that most logical rules can automatically apply to CTE defs; 2) In the main query and each subquery, there can only be at most one `WithCTE`, which means nested With-CTEs are combined. 2. Changed `CTESubstitution` rule so that if NOT in legacy mode, CTE defs will not be inlined immediately, but rather transformed into a `CTERelationRef` per reference. 3. Added new With-CTE rules: 1) `ResolveWithCTE` - to update `CTERelationRef`s with resolved output from corresponding `CTERelationDef`s; 2) `InlineCTE` - to inline deterministic CTEs or non-deterministic CTEs with only ONE reference; 3) `UpdateCTERelationStats` - to update stats for `CTERelationRef`s that are not inlined. 4. Added a CTE physical planning strategy to plan `CTERelationRef`s as an independent shuffle with round-robin partitioning so that such CTEs will only be materialized once and different references will later be a shuffle reuse. A current limitation is that With-CTEs mixed with SQL commands or DMLs will still go through the old inline code path because of our non-standard language specs and not-unified command/DML interfaces. ### Why are the changes needed? This is a correctness issue. Non-deterministic CTEs should produce the same output regardless of how many times it is referenced/used in query, while under the current implementation there is no such guarantee and would lead to incorrect query results. ### Does this PR introduce _any_ user-facing change? No. ### How was this patch tested? Added UTs. Regenerated golden files for TPCDS plan stability tests. There is NO change to the `simplified.txt` files, the only differences are expression IDs. Closes #33671 from maryannxue/spark-36447. Authored-by: Maryann Xue <maryann.xue@gmail.com> Signed-off-by: Wenchen Fan <wenchen@databricks.com> |
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Apache Spark
Spark is a unified analytics engine for large-scale data processing. It provides high-level APIs in Scala, Java, Python, and R, and an optimized engine that supports general computation graphs for data analysis. It also supports a rich set of higher-level tools including Spark SQL for SQL and DataFrames, pandas API on Spark for pandas workloads, MLlib for machine learning, GraphX for graph processing, and Structured Streaming for stream processing.
Online Documentation
You can find the latest Spark documentation, including a programming guide, on the project web page. This README file only contains basic setup instructions.
Building Spark
Spark is built using Apache Maven. To build Spark and its example programs, run:
./build/mvn -DskipTests clean package
(You do not need to do this if you downloaded a pre-built package.)
More detailed documentation is available from the project site, at "Building Spark".
For general development tips, including info on developing Spark using an IDE, see "Useful Developer Tools".
Interactive Scala Shell
The easiest way to start using Spark is through the Scala shell:
./bin/spark-shell
Try the following command, which should return 1,000,000,000:
scala> spark.range(1000 * 1000 * 1000).count()
Interactive Python Shell
Alternatively, if you prefer Python, you can use the Python shell:
./bin/pyspark
And run the following command, which should also return 1,000,000,000:
>>> spark.range(1000 * 1000 * 1000).count()
Example Programs
Spark also comes with several sample programs in the examples directory.
To run one of them, use ./bin/run-example <class> [params]. For example:
./bin/run-example SparkPi
will run the Pi example locally.
You can set the MASTER environment variable when running examples to submit
examples to a cluster. This can be a mesos:// or spark:// URL,
"yarn" to run on YARN, and "local" to run
locally with one thread, or "local[N]" to run locally with N threads. You
can also use an abbreviated class name if the class is in the examples
package. For instance:
MASTER=spark://host:7077 ./bin/run-example SparkPi
Many of the example programs print usage help if no params are given.
Running Tests
Testing first requires building Spark. Once Spark is built, tests can be run using:
./dev/run-tests
Please see the guidance on how to run tests for a module, or individual tests.
There is also a Kubernetes integration test, see resource-managers/kubernetes/integration-tests/README.md
A Note About Hadoop Versions
Spark uses the Hadoop core library to talk to HDFS and other Hadoop-supported storage systems. Because the protocols have changed in different versions of Hadoop, you must build Spark against the same version that your cluster runs.
Please refer to the build documentation at "Specifying the Hadoop Version and Enabling YARN" for detailed guidance on building for a particular distribution of Hadoop, including building for particular Hive and Hive Thriftserver distributions.
Configuration
Please refer to the Configuration Guide in the online documentation for an overview on how to configure Spark.
Contributing
Please review the Contribution to Spark guide for information on how to get started contributing to the project.