8b4862953a
### What changes were proposed in this pull request? [Delay scheduling](http://elmeleegy.com/khaled/papers/delay_scheduling.pdf) is an optimization that sacrifices fairness for data locality in order to improve cluster and workload throughput. One useful definition of "delay" here is how much time has passed since the TaskSet was using its fair share of resources. However it is impractical to calculate this delay, as it would require running simulations assuming no delay scheduling. Tasks would be run in different orders with different run times. Currently the heuristic used to estimate this delay is the time since a task was last launched for a TaskSet. The problem is that it essentially does not account for resource utilization, potentially leaving the cluster heavily underutilized. This PR modifies the heuristic in an attempt to move closer to the useful definition of delay above. The newly proposed delay is the time since a TasksSet last launched a task **and** did not reject any resources due to delay scheduling when offered its "fair share". See the last comments of #26696 for more discussion. ### Why are the changes needed? cluster can become heavily underutilized as described in [SPARK-18886](https://issues.apache.org/jira/browse/SPARK-18886?jql=project%20%3D%20SPARK%20AND%20text%20~%20delay) ### How was this patch tested? TaskSchedulerImplSuite cloud-fan tgravescs squito Closes #27207 from bmarcott/nmarcott-fulfill-slots-2. Authored-by: Nicholas Marcott <481161+bmarcott@users.noreply.github.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.