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Memory Heap Analysis with AppDynamics - AppSphere16
This document provides an overview of memory heap analysis using AppDynamics, detailing Java memory management, garbage collection processes, and tools available for monitoring memory issues. It covers essential topics such as the anatomy of the Java memory heap, object instance tracking, and automatic leak detection. Additionally, it emphasizes the importance of understanding garbage collection to prevent memory leaks and outlines the types of garbage collectors in Java.
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Memory Heap Analysis with AppDynamics - AppSphere16
- 1. Memory Heap Analysis withAppDynamics AppDynamics Version 4.2
- 2. APPDYNAMICS CONFIDENTIAL ANDPROPRIETARY 2 Notice The information and materials included in this presentation (collectively, the “Materials”) are the confidential and proprietary information of AppDynamics, Inc. (the “Company”). No part of the Materials may be reproduced, distributed, communicated or displayed in any form or by any means, or used to make any derivative work, without prior written permission from the Company. © 2016 AppDynamics, Inc. All rights reserved. All third party trademarks, including names, logos and brands, referenced by the Company in this presentation are property of their respective owners. All references to third party trademarks are for identification purposes only and shall be considered nominative fair use under trademark law.
- 3. Objectives By the endof this course, you will be able to: • Describe Java memory managementin detail • Visualize Java garbage collection processes with a profiler • Use the AppDynamics Memory dashboard to monitor and troubleshootgarbage collection issues in your applications • Use AppDynamics ObjectInstance Tracking and Automatic Leak Detection features to find the root cause of many common memory issues in Java applications • Describe the issues with ClassLoader leaks and other PermGen / MetaSpace issues, and how to preventthem APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 3 Course After completing the labs in the course,you will be able to use Object Instance Tracking,and Automatic Leak Detection to help troubleshootmemory problems and find the root cause of these issues. Labs
- 4. APPDYNAMICS CONFIDENTIAL ANDPROPRIETARY 4 Topic 1 Garbage Collection Explained A. How Garbage Collection Works In Java B. The Anatomy Of The Java Memory Heap C. Using A Profiler To Visualize The Java Memory Heap Topic 2 Memory Heap Analysis Tooling & Workflows A. Available Tooling B. Using Automatic Leak Detection And Object Instance Tracking C. OutOfMemoryError ! = Memory Leak D. The Problem Of ClassLoader Leaks Memory Heap Analysis with AppDynamics Agenda
- 5. APPDYNAMICS CONFIDENTIAL ANDPROPRIETARY 5 Topic 1 Garbage Collection Explained A. How Garbage Collection Works In Java B. The Anatomy Of The Java Memory Heap C. Using A Profiler To Visualize The Java Memory Heap Agenda Memory Heap Analysis with AppDynamics
- 6. Java Memory Management MostJava developers know thatJava uses automatic memory management,and that a garbage collector manages memory withoutthe need for explicit developer interaction. Few of us know the details and limitations of the garbage collector’s inner workings,and even fewer know what to look for in order to ensure that a Java application is notinadvertently preventing the garbage collector from doing its job effectively. APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 6 Concepts, Details & Limitations We’ll explain the concepts behind memory management,and go into detail abouthow garbage collection works,then we’ll cover the types of garbage collectors available to Java virtual machines,and some situations in which they might be useful. Finally,we’ll actually look at garbage collection in action with the help of a profiler.
- 7. Garbage Collection Concepts First,what we all know about Java memory management and garbage collection • Java collects memory automatically by running one or more garbage collector threads thatremove objects that are no longer needed by the application • Therefore, Java can not produce a memory leak per se, right? We’ll not really.We’ll examine this question further. The biggestreason that the 2nd bulleton the left is not always true is that what Java thinks is “no longer needed” may differ from what you, the developer think, so an application may leak memory because objects that you think are “no longer needed” are keptin memory by Java. APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 7 Concepts, Details & Limitations BAD NEWS Knowing how the garbage collector works is more complicated than it seems. GOOD NEWS Java generally “does the right thing”,so if you know how the garbage collector works, you should be able to avoid most memory management issues
- 8. Knowing How TheGarbage Collector Works Because one can not force the garbage collector to do its job on command, this is more complex than following simple guidelines like • Setting all objects to null when no longer needed • Calling System.gc() • Using certain design patterns Each situation you encounter may be different and requires analysis. Rather than following a recipe,it is best to understand conceptually how the garbage collection process works. Once you know the conceptual framework,you will usually be able to analyze a situation and make the right decisions to avoid memory issues. APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 8 Concepts, Details & Limitations
- 9. APPDYNAMICS CONFIDENTIAL ANDPROPRIETARY 9 Topic 1 Garbage Collection Explained A. How Garbage Collection Works In Java B. The Anatomy Of The Java Memory Heap C. Using A Profiler To Visualize The Java Memory Heap Memory Heap Analysis with AppDynamics Agenda
- 10. Setting The Stage Thereare many kinds of Java applications, and, as stated earlier, they are all different and need to be analyzed. However, we can make some basic assumptions that will help narrow the space to a manageable one. 1. Our target application will be a Java Web Application running on an Oracle Java 7+ JVM 2. We’ll use Tomcat Application Server,but most Java EE servers have similar memory managementcharacteristics 3. The JVM is using the -server switch, and therefore using a server-optimized garbage collector 4. The JVM is not using the G1 garbage collector APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 10
- 11. The HotSpot MemorySpace APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 11 A HotSpot JVM contains a number of different memory spaces In our discussions of memory management, we’ll concentrate on the heap,as it contains the majority of application objectinstances that are garbage collected during the life of the application The various memory spaces are The heap contains (most) objectreferences. This is segmented into different regions or generations Stacks and other memory spaces includes the stacks as well as method, thread, native, and JVM execution spaces,and are smaller than the heap
- 12. Short- v. Long-LivedObjects In Web Apps APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 12 In our discussions of memory management,we’ll concentrate on the heap,as it contains the majority of application objectinstances that are garbage collected during the life of the application. OBJECT AGE NUMBEROFOBJECTS Web apps contain many more short-lived than long-lived objects, and show an inverse relationship between the number of instances and their age
- 13. Generational Heap Structure APPDYNAMICSCONFIDENTIAL AND PROPRIETARY 13 JVM Heap
- 14. Generational Heap Structure APPDYNAMICSCONFIDENTIAL AND PROPRIETARY 14 JVM Heap Minor Collection STOP THE WORLD Major Collection STOP THE WORLD
- 15. Generational Heap Structure APPDYNAMICSCONFIDENTIAL AND PROPRIETARY 15 JVM Heap Total Collection STOP THE WORLD
- 16. Generational Heap Structure APPDYNAMICSCONFIDENTIAL AND PROPRIETARY 16 JVM Heap Minor Collection STOP THE WORLD Major Collection STOP THE WORLD
- 17. Ways to Controlthe Shape & Size of the Heap APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 17 -Xms //initial total heap size -Xmx //Maximum total heap size; allows the heap to grow from initial to maximum size -Xmn //Young generation size -XX:PermSize //Initial PermGen size -XX:MaxPermSize //Maximum PermGen size; allows PermGen to grow from initial to maximum size Java has a number of system switches that allow developers to control the size or relative size of the different parts of the heap
- 18. APPDYNAMICS CONFIDENTIAL ANDPROPRIETARY 18 Topic 1 Garbage Collection Explained A. How Garbage Collection Works In Java B. The Anatomy Of The Java Memory Heap C. Using A Profiler To Visualize The Java Memory Heap Memory Heap Analysis with AppDynamics Agenda
- 19. Types Of GarbageCollectors APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 19 SerialGC Optimized for client applications with small memory footprints ParallelGC Uses multiple threads to GC. Optimized for situations in which throughputis importantand long pauses are acceptable,such as batch processing Concurrent Mark-Sweep(CMS) GC Attempts to minimize pauses.Optimized for server JVMs Garbage First (G1) GC Attempts to improve on CMS GC performance while providing configurable pause thresholds
- 20. Serial GC APPDYNAMICS CONFIDENTIALAND PROPRIETARY 20 -XX:+UseSerialGC Java has a number of system switches that allow developers to control the size or relative size of the different parts of the heap • Uses a single thread for both major and minor collections • Uses compacting in the Old Gen to move surviving objects to contiguous memory,which makes it faster to allocate memory for new objects • Best for clientapplications with small memory footprints To use the SerialGC collector,add the following switch to your Java command: STOP THE WORLD PAUSE STOP THE WORLD PAUSE
- 21. Parallel GC APPDYNAMICS CONFIDENTIALAND PROPRIETARY 21 -XX:+UseParallelGC //(default) parallel Young Gen + serial compacting Old Gen -XX:+UseParallelOldGC //parallel Young Gen + parallel compacting Old Gen Java has a number of system switches that allow developers to control the size or relative size of the different parts of the heap • Uses multiple threads,generally more efficientthan SerialGC • Will perform better than SerialGC on host with 3+ CPUs • Optimized for throughput.However,long pauses will occur for major collections • Best for batch processing environments thatrequire high throughput,but not high responsiveness The ParallelGC collector comes in two flavors: STOP THE WORLD PAUSE STOP THE WORLD PAUSE
- 22. Concurrent Mark-Sweep(CMS) GC APPDYNAMICSCONFIDENTIAL AND PROPRIETARY 22 -XX:+UseConcMarkSweepGC //in addition, the number of threads used is set with -XX:ParallelCMSThreads=<n> //where <n> is the number of threads required Java has a number of system switches that allow developers to control the size or relative size of the different parts of the heap • Only an Old Gen collector.Uses the same algorithm as ParallelGC for Young Gen • No compaction.If fragmentation is an issue, switch to ParallelGC or use larger heap • Optimized for low pause length relative to ParallelGC • Performs majority of GC work concurrently with the application threads (less Stop The World time). • Best for server apps that need to be highly responsive The CMS GC collector is invoked with: STOP THE WORLD PAUSE INITIAL MARK CONCURRENTMARK REMARK
- 23. Garbage First (G1)GC APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 23 -XX:+UseG1GC //in addition, the maximum pause length can be set with -XX:MaxGCPauseMillis=<n> //the default is 200 Java has a number of system switches that allow developers to control the size or relative size of the different parts of the heap • Is a parallel,concurrent,incrementally compacting low-pause collector – the most advanced general purpose collector available • Divides the heap into small regions of equal size, rather than Young and Old generations • Focuses on collecting regions with few live objects • Always compacts objects into differentregion,and leaves the current region empty • Decreases pause time, because whole region can be collected in one operation;Includes a pause-time threshold control The CMS GC collector is invoked with
- 24. Instructor Demo APPDYNAMICS CONFIDENTIALAND PROPRIETARY 24 Visualizing the Garbage Collection Process
- 25. Java Garbage CollectionIn Action APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 25 To take the concepts we’ve learned aboutgarbage collection and make them more concrete,we’ll actually take a look at garbage collection in action We will use the standard Java profiler that comes with the JDK, JVisualVM,on a web application running on Tomcat 7 and JDK 7, and see whatthe memory heap actually looks like in real-time
- 26. APPDYNAMICS CONFIDENTIAL ANDPROPRIETARY 26 Topic 2 Memory HeapAnalysis Tooling & Workflows A. Available Tooling B. Using Automatic Leak Detection And Object Instance Tracking C. OutOfMemoryError ! = Memory Leak D. The Problem Of ClassLoader Leaks Memory Heap Analysis with AppDynamics Agenda
- 27. Node-Level Memory Dashboard APPDYNAMICSCONFIDENTIAL AND PROPRIETARY 27 AGENTS Shows state of all AppDynamics agents associated with this node • App Server Agent • Machine Agent • Agent Diagnostics HARDWARE Shows CPU/ Memory Utilization and File/Network I/O metrics MEMORY Shows JVM/CLR Heap state •Object Instance Tracking •Automatic Leak Detection Provides detailed information on the state of each node
- 28. Object Instance Tracking(OIT) APPDYNAMICSCONFIDENTIAL AND PROPRIETARY 28 Shows the allocated trend for • Top 20 Application Classes • Top 20 System Classes • Custom Classes OIT allows a drill-down into how objects are being instantiated and which part of your application code is creating each objecttype. It is useful for diagnostic memory leak/memory thrash situations.
- 29. APPDYNAMICS CONFIDENTIAL ANDPROPRIETARY 29 Topic 2 Memory HeapAnalysis Tooling & Workflows A. Available Tooling B. Using Automatic Leak DetectionAnd Object Instance Tracking C. OutOfMemoryError ! = Memory Leak D. The Problem Of ClassLoader Leaks Memory Heap Analysis with AppDynamics Agenda
- 30. Automatic Leak Detection(ALD) APPDYNAMICSCONFIDENTIAL AND PROPRIETARY 30 • Monitors all collection classes in your application • Shows any collections thatare growing monotonously for a long time • Useful for detecting collection- based memory leaks • Can cause significant overhead:Best used in dev/test. If used in production, enable on a single node rather than the whole tier
- 31. Instructor Demo APPDYNAMICS CONFIDENTIALAND PROPRIETARY 31 Workflow for Memory Heap Analysis
- 32. Using Object InstanceTracking APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 32 We will cause our web application to experience a memory leak by repeatedly adding instances ofan objectin memory. Then we’ll monitor the app with Object Instance Tracking and see if we can find the objects responsible for the memory leak. If we do find some suspect classes, we’ll start an allocation tracking session to see where these objects are being created in our code.
- 33. Using Automatic LeakDetection APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 33 We will now cause our web application to experience a collection- based memory leak. Then we’ll monitor with Automatic Leak Detection and see if ALD can pinpoint the leaking collection. If we do find a culprit, we can run allocation sessions to find out what is in the collection and where in our code it is being allocated.
- 34. APPDYNAMICS CONFIDENTIAL ANDPROPRIETARY 34 Topic 2 Memory HeapAnalysis Tooling & Workflows A. Available Tooling B. Using Automatic Leak Detection And Object Instance Tracking C. OutOfMemoryError ! = Memory Leak D. The Problem Of ClassLoader Leaks Memory Heap Analysis with AppDynamics Agenda
- 35. Non-Memory Leak Causeof OutOfMemoryError APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 35 Heap is too small for (normal) operation Overload causes heap to fill OutOfMemoryError in PermGen Misconfiguration or Capacity Mismatch Misconfiguration or Capacity Mismatch Misconfiguration (but see ClassLoader leak issue, discussed next) OutOfMemoryError can happen for a number of reasons
- 36. APPDYNAMICS CONFIDENTIAL ANDPROPRIETARY 36 Topic 2 Memory HeapAnalysis Tooling & Workflows A. Available Tooling B. Using Automatic Leak Detection And Object Instance Tracking C. OutOfMemoryError ! = Memory Leak D. The Problem Of ClassLoader Leaks Memory Heap Analysis with AppDynamics Agenda
- 37. ClassLoader Reference CannotBe Garbage APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 37 Except sometimes Any time that a class is loaded inside your application by the system ClassLoader,a memory leak may result Given the fact that the ClassLoader has references to every Class objectin your application,this can chew up the PermGen quickly • Best way to explain is to look at an example.An excellent one is the issue of loading JDBC drivers • The below code loads a JDBC driver Class.forName(“com.mysql.jdbc.Driver”); Connection c = DriverManager.getConnection(“jdbc:mysql://dbhost/dbName”); …
- 38. Many So-Called SystemClasses APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 38 This can occur with any of them While the JDBC driver is a very common example, what I’m about to show you can happen with any of the following • Bean introspection caches • Shutdown hooks • Custom defaultauthenticator • Custom security providers • Custom MBeans,ThreadGroups,or PropertyEditors Now back to loading our JDBC driver…
- 39. Reference Map FromJRE System Object to Your Application ClassLoader APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 39
- 40. General Rule ForWeb Apps APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 40 The general rule applies to many other System classes and resources • If you load a class in your application thatwill register itselfwith the system, when your web application is reloaded,the JVM may not be able to garbage collectthe ClassLoader • Any time you have an OutOfMemoryError in PermGen, you should suspect a ClassLoader leak • Since many classes register themselves with a central system registry, this is often called the “central registration problem” and itleads directly to PermGen memory leaks as web applications are redeployed by the app server • The problem can be particularly severe in continuous integration environments in which applications are redeployed regularly The way to solve the JDBC issue in our example is easy — simply move the JDBC driver class from your application to the common app server
- 41. What We LearnedToday APPDYNAMICS CONFIDENTIAL AND PROPRIETARY 41 • Describe in detail the structure of the Java HotSpot JVM memory space • Understand the process of garbage collection and how objects are promoted through the differentmemory spaces in the Java heap • Describe the differenttypes of garbage collectors available in Java,and what conditions they are optimized for • Use AppDynamics memory managementtools like ALD and OIT to diagnose memory issues in your application • Understand the causes of ClassLoader memory leaks and how to avoid them You should now be able to complete a few tasks
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- 47. Thank You Please fillout the survey: https://www.surveymonkey.com/r/AppDynamicsUniversity Your feedback is very important to us. We use it to help us improve our content and incorporate new features to keep our courses relevantfor our audience. Ray Baco ray.baco@appdynamics.com