Book Image

Clojure High Performance Programming

By : Shantanu Kumar
Book Image

Clojure High Performance Programming

By: Shantanu Kumar

Overview of this book

<p>Clojure is a young, dynamic, functional programming language that runs on the Java Virtual Machine. It is built with performance, pragmatism, and simplicity in mind. Like most general purpose languages, Clojure’s features have different performance characteristics that one should know in order to write high performance code.<br /><br />Clojure High Performance Programming is a practical, to-the-point guide that shows you how to evaluate the performance implications of different Clojure abstractions, learn about their underpinnings, and apply the right approach for optimum performance in real-world programs.<br /><br />This book discusses the Clojure language in the light of performance factors that you can exploit in your own code.</p> <p>You will also learn about hardware and JVM internals that also impact Clojure’s performance. Key features include performance vocabulary, performance analysis, optimization techniques, and how to apply these to your programs. You will also find detailed information on Clojure's concurrency, state-management, and parallelization primitives.</p> <p>This book is your key to writing high performance Clojure code using the right abstraction, in the right place, using the right technique.</p>
Table of Contents (15 chapters)
Clojure High Performance Programming
Credits
About the Author
Acknowledgments
About the Reviewers
www.PacktPub.com
Preface
Index

Measuring latency with Criterium


Clojure has a neat little macro called time that evaluates the body of code passed to it and then prints out the time it took and simply returns the value. However, we can note that often the time taken to execute the code varies quite a bit across various runs.

user=> (time (reduce + (range 100000)))
"Elapsed time: 112.480752 msecs"
4999950000
user=> (time (reduce + (range 1000000)))
"Elapsed time: 387.974799 msecs"
499999500000

There are several reasons associated to this variance in behavior. When cold started, the JVM has its heap segments empty and is unaware of the code path. As the JVM keeps running, the heap fills up and the GC patterns start becoming noticeable. The JIT compiler gets a chance to profile the different code paths and optimize them. Only after quite some GC and JIT compilation rounds does the JVM performance get less unpredictable.

Criterium (https://github.com/hugoduncan/criterium) is a Clojure library to scientifically measure...