Uploaded byFilippo Pacifici
Scala profiling
The document discusses how Java profiling methods can be applied to Scala programs, given that Scala is compiled into bytecode and runs on the JVM. It covers various profiling techniques for methods and memory, highlights profiling tools, and provides insights into Scala's data structures and performance optimizations. The presentation emphasizes understanding Scala's translation into bytecode and offers tips on GC selection and memory management for improved performance.
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Scala profiling
- 1. SCALA PROFILING (for Java developers) Filippo Pacifici mercoledì 23 maggio 12
- 2. Who am I • Filippo Pacifici • Twitter: OddId_ • mail: filippo.pacifici@gmail.com • Blog: http://outofmemoryblog.blogspot.com • One of the 9M devs thinking Java is not so bad • recently started looking at Scala mercoledì 23 maggio 12
- 3. What’s this allabout? • Apply Java profiling methods to Scala programs • How do we deal with performance in Java? • Is it the same in Scala? • How do we optimize a JVM for Scala applications? mercoledì 23 maggio 12
- 4. Java profiling 101 mercoledì23 maggio 12
- 5. Java profiling 101 • Goals: • troubleshoot performance problems • estimate application performance • estimate application scalability mercoledì 23 maggio 12
- 6. Java profiling 101 • Ehi, I use Scala, why should I care about Java profiling? • Scala compiled in byte code and runs in a JVM • We can profile a Scala application as it was Java • We can use the same tools • I am not aware of alternatives mercoledì 23 maggio 12
- 7. Java methods profiling • Tracks methods invocations • Runtime instrumentation • Time analysis mercoledì 23 maggio 12
- 8. Java memory profiling • Dumps heap content • Browse objects in the heap • Memory usage analysis mercoledì 23 maggio 12
- 9. Profiling tools • Method profiling • Java Visual VM (embedded in JDK) • Yourkit, Dynatrace, etc. • Memory profiling • Eclipse MAT (www.eclipse.org/ mat) • Yourkit, Dynatrace, etc. mercoledì 23 maggio 12
- 10. Back to Scala... • We won’t find Scala specific constructs • Need to know how Scala is translated into bytecode • Goals: • Identify methods generated by Scala compilers • Characterize Scala data structures in memory mercoledì 23 maggio 12
- 11. Scala Functions mercoledì 23maggio 12
- 12. Short discouraging comparative demo mercoledì 23 maggio 12
- 13. Scala functions vsbyte code • Classic functions converted in methods • First class function do not exist in Java • Anonymous classes extending scala.runtime.AbstractFunction • apply method to execute. mercoledì 23 maggio 12
- 14. AbstractFunction • AbstractFunction2 • takes 2 input parameters • One apply method per combination of input and output types • example apply.mcFID • F= returns float • I takes one Int • D takes one Double mercoledì 23 maggio 12
- 15. AbstractFunction • Find the call in the profile: • anonfun => instance of the anonymous class • main$1 => first anonymous class defined in main method mercoledì 23 maggio 12
- 16. Functions in theheap • Each instance of AbstractFunction present in the heap • Very small impact • Stateless mercoledì 23 maggio 12
- 17. Where do weuse them? • Our program did not contain any anonymous function, right? • AbstractFunction used: • For first class functions • For closures • For partially applied functions • To manage for loops blocks • To manage filter logic in for loops mercoledì 23 maggio 12
- 18. Performance impact • Is this a performance impact? • Scala compiler performs optimizations: • Same anonymous functions reused (avoid multiple instantiations) • Anonymous functions doing the same thing are shared • Attention to partially applied: • New function created. mercoledì 23 maggio 12
- 19. Some examples mercoledì 23maggio 12
- 20. Scala data structures (Collections in heap dump) mercoledì 23 maggio 12
- 21. Scala Lists • A Scala view: • Linked lists (single link) • abstract class List + two case classes: :: and Nil mercoledì 23 maggio 12
- 22. Scala Lists • A byte code view: • Case classes become inner classes: • :: becomes $colon$colon • Nil becomes Nil mercoledì 23 maggio 12
- 23. Scala Lists • Heads and elements have the same type mercoledì 23 maggio 12
- 24. Scala Lists • What about mutable lists? • ListBuffer • Wrapper on a Linked List • Keeps an additional reference to the last element: last0 mercoledì 23 maggio 12
- 25. Scala Sets • Immutable sets • scala.collection.immutable.Set • Case classes for different sizes • HashSet over 5 elements mercoledì 23 maggio 12
- 26. Scala Maps • Immutable: • small number of elements: scala.collections.immutable.Map$MapN • N = number of elements • over 5 elements: scala.collection.immutable.HashMap • Mutable: scala.collection.mutable.HashMap mercoledì 23 maggio 12
- 27. Map and Setsexamples mercoledì 23 maggio 12
- 28. Primitive types boxing mercoledì23 maggio 12
- 29. Primitive types and generics • Type parameters cannot be primitive in generic types. • Scala systematically boxes and unboxes them to Object • scala.runtime.BoxesRunTime methods mercoledì 23 maggio 12
- 30. Basic tuning tips mercoledì23 maggio 12
- 31. Exploit tail recursion • Long recursion • Long stack • Performance impact on stack size • Scala compiler recognizes tail recursion • Recursive call must be the last operation of the method • Scala transforms it into iterative form mercoledì 23 maggio 12
- 32. Can’t exploit tail recursion? • If (and only if) you run out of stack space (frequent java.lang.StackOverflowError): • -Xss JVM option sets stack size • example: -Xss2048k • Normally limited at OS level • Each thread statically allocates stack size: • pay attention mercoledì 23 maggio 12
- 33. Memory structure • Optimize for small, short lived objects • Anonymous functions: • small • frequently instantiated • Use a big young space • GC is fast and frequent • Objects do not get promoted mercoledì 23 maggio 12
- 34. Memory structure • What about the perm gen? • Anonymous classes reused • No insane usage of proxies • No specific issues mercoledì 23 maggio 12
- 35. Which GC shouldI use? • Depends on your application requirements • The same consideration done for Java still hold • Need throughput : parallel GC • Need response time : CMS • You are brave : G1 mercoledì 23 maggio 12
- 36.