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62 lines
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8 years ago
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###JMH-Benchmark module
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This module contains benchmarks written using [JMH](http://openjdk.java.net/projects/code-tools/jmh/) from OpenJDK.
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Writing correct micro-benchmarks is Java (or another JVM language) is difficult and there are many non-obvious pitfalls (many
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due to compiler optimizations). JMH is a framework for running and analyzing benchmarks (micro or macro) written in Java (or
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another JVM language).
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For help in writing correct JMH tests, the best place to start is the [sample code](http://hg.openjdk.java.net/code-tools/jmh/file/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/) provided
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by the JMH project.
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Typically, JMH is expected to run as a separate project in Maven. The jmh-benchmarks module uses
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the [gradle shadow jar](https://github.com/johnrengelman/shadow) plugin to emulate this behavior, by creating the required
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uber-jar file containing the benchmarking code and required JMH classes.
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JMH is highly configurable and users are encouraged to look through the samples for suggestions
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on what options are available. A good tutorial for using JMH can be found [here](http://tutorials.jenkov.com/java-performance/jmh.html#return-value-from-benchmark-method)
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###Gradle Tasks / Running benchmarks in gradle
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If no benchmark mode is specified, the default is used which is throughput. It is assumed that users run
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the gradle tasks with './gradlew' from the root of the Kafka project.
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* jmh-benchmarks:shadowJar - creates the uber jar required to run the benchmarks.
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* jmh-benchmarks:jmh - runs the `clean` and `shadowJar` tasks followed by all the benchmarks.
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### Using the jmh script
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If you want to set specific JMH flags or only run a certain test(s) passing arguments via
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gradle tasks is cumbersome. Instead you can use the `jhm.sh` script. NOTE: It is assumed users run
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the jmh.sh script from the jmh-benchmarks module.
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* Run a specific test setting fork-mode (number iterations) to 2 :`./jmh.sh -f 2 LRUCacheBenchmark`
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* By default all JMH output goes to stdout. To run a benchmark and capture the results in a file:
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`./jmh.sh -f 2 -o benchmarkResults.txt LRUCacheBenchmark`
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NOTE: For now this script needs to be run from the jmh-benchmarks directory.
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### Running JMH outside of gradle
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The JMH benchmarks can be run outside of gradle as you would with any executable jar file:
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`java -jar <kafka-repo-dir>/jmh-benchmarks/build/libs/kafka-jmh-benchmarks-all.jar -f2 LRUCacheBenchmark`
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### JMH Options
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Some common JMH options are:
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```text
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-e <regexp+> Benchmarks to exclude from the run.
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-f <int> How many times to fork a single benchmark. Use 0 to
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disable forking altogether. Warning: disabling
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forking may have detrimental impact on benchmark
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and infrastructure reliability, you might want
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to use different warmup mode instead.
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-o <filename> Redirect human-readable output to a given file.
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-v <mode> Verbosity mode. Available modes are: [SILENT, NORMAL,
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EXTRA]
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```
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To view all options run jmh with the -h flag.
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