44a71741d5
## What changes were proposed in this pull request?
This PR contains 3 optimizations:
1) it improves significantly the operation `--` on `AttributeSet`. As a benchmark for the `--` operation, the following code has been run
```
test("AttributeSet -- benchmark") {
val attrSetA = AttributeSet((1 to 100).map { i => AttributeReference(s"c$i", IntegerType)() })
val attrSetB = AttributeSet(attrSetA.take(80).toSeq)
val attrSetC = AttributeSet((1 to 100).map { i => AttributeReference(s"c2_$i", IntegerType)() })
val attrSetD = AttributeSet((attrSetA.take(50) ++ attrSetC.take(50)).toSeq)
val attrSetE = AttributeSet((attrSetC.take(50) ++ attrSetA.take(50)).toSeq)
val n_iter = 1000000
val t0 = System.nanoTime()
(1 to n_iter) foreach { _ =>
val r1 = attrSetA -- attrSetB
val r2 = attrSetA -- attrSetC
val r3 = attrSetA -- attrSetD
val r4 = attrSetA -- attrSetE
}
val t1 = System.nanoTime()
val totalTime = t1 - t0
println(s"Average time: ${totalTime / n_iter} us")
}
```
The results are:
```
Before PR - Average time: 67674 us (100 %)
After PR - Average time: 28827 us (42.6 %)
```
2) In `ColumnPruning`, it replaces the occurrences of `(attributeSet1 -- attributeSet2).nonEmpty` with `attributeSet1.subsetOf(attributeSet2)` which is order of magnitudes more efficient (especially where there are many attributes). Running the previous benchmark replacing `--` with `subsetOf` returns:
```
Average time: 67 us (0.1 %)
```
3) Provides a more efficient way of building `AttributeSet`s, which can greatly improve the performance of the methods `references` and `outputSet` of `Expression` and `QueryPlan`. This basically avoids unneeded operations (eg. creating many `AttributeEqual` wrapper classes which could be avoided)
The overall effect of those optimizations has been tested on `ColumnPruning` with the following benchmark:
```
test("ColumnPruning benchmark") {
val attrSetA = (1 to 100).map { i => AttributeReference(s"c$i", IntegerType)() }
val attrSetB = attrSetA.take(80)
val attrSetC = attrSetA.take(20).map(a => Alias(Add(a, Literal(1)), s"${a.name}_1")())
val input = LocalRelation(attrSetA)
val query1 = Project(attrSetB, Project(attrSetA, input)).analyze
val query2 = Project(attrSetC, Project(attrSetA, input)).analyze
val query3 = Project(attrSetA, Project(attrSetA, input)).analyze
val nIter = 100000
val t0 = System.nanoTime()
(1 to nIter).foreach { _ =>
ColumnPruning(query1)
ColumnPruning(query2)
ColumnPruning(query3)
}
val t1 = System.nanoTime()
val totalTime = t1 - t0
println(s"Average time: ${totalTime / nIter} us")
}
```
The output of the test is:
```
Before PR - Average time: 733471 us (100 %)
After PR - Average time: 362455 us (49.4 %)
```
The performance improvement has been evaluated also on the `SQLQueryTestSuite`'s queries:
```
(before) org.apache.spark.sql.catalyst.optimizer.ColumnPruning 518413198 / 1377707172 2756 / 15717
(after) org.apache.spark.sql.catalyst.optimizer.ColumnPruning 415432579 / 1121147950 2756 / 15717
% Running time 80.1% / 81.3%
```
Also other rules benefit especially from (3), despite the impact is lower, eg:
```
(before) org.apache.spark.sql.catalyst.analysis.Analyzer$ResolveReferences 307341442 / 623436806 2154 / 16480
(after) org.apache.spark.sql.catalyst.analysis.Analyzer$ResolveReferences 290511312 / 560962495 2154 / 16480
% Running time 94.5% / 90.0%
```
The reason why the impact on the `SQLQueryTestSuite`'s queries is lower compared to the other benchmark is that the optimizations are more significant when the number of attributes involved is higher. Since in the tests we often have very few attributes, the effect there is lower.
## How was this patch tested?
run benchmarks + existing UTs
Closes #22364 from mgaido91/SPARK-25379.
Authored-by: Marco Gaido <marcogaido91@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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Apache Spark
Spark is a fast and general cluster computing system for Big Data. 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 Spark 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.)
You can build Spark using more than one thread by using the -T option with Maven, see "Parallel builds in Maven 3". 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 1000:
scala> sc.parallelize(1 to 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 1000:
>>> sc.parallelize(range(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.