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### What changes were proposed in this pull request? `hash()` and `xxhash64()` cannot be used on elements of `Maptype`. A new configuration `spark.sql.legacy.useHashOnMapType` is introduced to allow users to restore the previous behaviour. When `spark.sql.legacy.useHashOnMapType` is set to false: ``` scala> spark.sql("select hash(map())"); org.apache.spark.sql.AnalysisException: cannot resolve 'hash(map())' due to data type mismatch: input to function hash cannot contain elements of MapType; line 1 pos 7; 'Project [unresolvedalias(hash(map(), 42), None)] +- OneRowRelation ``` when `spark.sql.legacy.useHashOnMapType` is set to true : ``` scala> spark.sql("set spark.sql.legacy.useHashOnMapType=true"); res3: org.apache.spark.sql.DataFrame = [key: string, value: string] scala> spark.sql("select hash(map())").first() res4: org.apache.spark.sql.Row = [42] ``` ### Why are the changes needed? As discussed in Jira, SparkSql's map hashcodes depends on their order of insertion which is not consistent with the normal scala behaviour which might confuse users. Code snippet from JIRA : ``` val a = spark.createDataset(Map(1->1, 2->2) :: Nil) val b = spark.createDataset(Map(2->2, 1->1) :: Nil) // Demonstration of how Scala Map equality is unaffected by insertion order: assert(Map(1->1, 2->2).hashCode() == Map(2->2, 1->1).hashCode()) assert(Map(1->1, 2->2) == Map(2->2, 1->1)) assert(a.first() == b.first()) // In contrast, this will print two different hashcodes: println(Seq(a, b).map(_.selectExpr("hash(*)").first())) ``` Also `MapType` is prohibited for aggregation / joins / equality comparisons #7819 and set operations #17236. ### Does this PR introduce any user-facing change? Yes. Now users cannot use hash functions on elements of `mapType`. To restore the previous behaviour set `spark.sql.legacy.useHashOnMapType` to true. ### How was this patch tested? UT added. Closes #27580 from iRakson/SPARK-27619. Authored-by: iRakson <raksonrakesh@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, 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.