Plumbing Memory Leaks

Transcript

1. Plumbing memory leaks
2. Who am I • Nikita Salnikov-Tarnovski! • Founder and Master Developer from ! • We solve performance problems! • @iNikem, @JavaPlumbr
3. JVM and memory • When JVM runs, it uses different regions of memory! • Native! • Heap (Young generation and Old generation)! • Permanent Generation
4. Java memory management • JVM has automatic memory management! • Developers don’t think about it! • They just new and go on
5. Garbage goes to Heap 5
6. Garbage Collector 6
7. Garbage Collector • Subsystem of JVM for reclaiming “unused” memory! • Memory occupied by unused objects! • Not JVM specific, many runtimes have it! • Different algorithms
8. Memory problems • Memory leaks! • Long GC pauses! • GC overhead
9. GC “wizardry” • GC is not mind reading magician! • It always works by very specific and strict algorithm! • “No references, thus garbage”
10. Reachability • Mark all GC roots as “reachable”! • Mark all objects referenced from “reachable” objects as “reachable” too! • Repeat until all reachable objects found! • Everything else is garbage and can be thrown away
11. Memory leak • Reachable object(s), that will never be used by application! • Repetitive creation of such objects
12. Examples • Caches without look-ups and eviction! • String.substring! • Immortal threads! • Unclosed IO streams! • Storages with longer lifespan than stored values
13. Symptoms • OutOfMemoryError: XXX! • Application is very slow due to excessive GC
14. Not a memory leak • Too high allocation rate! • Cache with wrong size! • Trying to load too much data at once! • Fat data structures
15. GC pauses • GC has to stop the world to do his job! • These pauses are almost unpredictable! • Huge impact on users’ perception
16. GC overhead • GC shares CPU with your application! • Whenever he wants CPU, he just takes it
17. Tools • Profilers! • Heap dump analyzers! • APM! • command line tools of JDK
18. Results • crashes, sometimes together with the application;! • tons of flickering dashboards, graphics, buttons, bells and whistles, but no answer;! • console full of cryptic text and java class names;! • … or application adapted for snails and turtles, with response times increased 5-350 times.! • http://plumbr.eu/blog/solving-outofmemoryerror-no- tools-will-help-you
19. Memory Analyzer (MAT) • From Eclipse! • It really works for finding memory leaks! • If you have experience! • http://www.eclipse.org/mat/
20. Plumbr • Java agent monitoring your application! • In case of problem reports you exact details! • Memory leak, class loader leaks! • GC related problems soon
21. Solving performance problems is hard. ! We don’t think it needs to be.