Tools and Tips to Diagnose Performance Issues

Tools and Tips to Diagnose Performance Issues Claudio Miranda Summa Technologies 3320

2 Objective Learn some tips and tools to better diagnose and solve the most common performance issues of Java applications. The main focus going on to diagnose memory and CPU problems.

3 Disclaimer The presented tools are based on the author's experience. These arguments can be applied to development and production systems

4 Disclaimer 2 There are plenty of others free and commercial tools available, some better suited to specific tasks, other tools can be easy or complex to use, it all depends of: Time Money

5 AGENDA > Where it all begins > Tools and tips to diagnose problems > Application and system performance > General tips

7 Where it all begins > No performance requirements at project level > Traps – “The application is too slow” – “Speed it up at all costs” How much to tune ? It is necessary to have performance numbers to work with > Typical numbers – Tx/s (Average transactions per second) – Concurrent users – Number of sessions

8 Where it all begins > What is a transaction ? – Database – Messaging – Connector – Filesystem – Is “two phase commit” required ? > Call it a business transaction – Example: 2 DB inserts + 1 messaging – Identify the hot spots

9 Where it all begins > Where is the problem ? – Memory – I/O – Networking – CPU >

10 Where it all begins > Personal diagnose and solve steps – Analysis => What is the matter ? – Priority => Is the application down or slow ? – Diagnose => Where is the problem ? – Solution => How to solve it ?  Sledgehammer way  Best practices – Tests => Make sure it will not happen again – Documentation => To remember what happened

12 Tools and Tips > Memory issues – Memory Leak – OutOfMemoryError (OOME) > CPU issues – High CPU usage – Threads > Garbage Collector

13 Tools and Tips Each tool and tip has different level of intrusion on the overall system. It ranges from simple monitoring (with ready to use tools) to profiling and debugging. That is one key point, to consider which approach to use, to diagnose a problem

14 Tools and Tips > Monitoring – Non intrusive – No pre-configuration – Monitor production systems – Easy to use > Profiling and Debugging – Easily shows where is the problem – Nice graphics – Needs to restart system – Slowdown system runtime – Additional settings – Can distort results

15 Tools and Tips Diagnose Memory Issues

16 Tools and Tips - Memory > Required steps – How much physical memory is available – How many programs are using it – Who is the memory hunger ?  What are the VM parameters ? – Application did entire life cycle to prevent new classes being loaded  Initial load time

17 Tools and Tips – Monitoring Memory > How much Physical memory > Who is the memory hunger > Monitoring: top – RES = Physical memory

18 Tools and Tips – Monitoring Memory Java heap space > Monitoring: jmap > GC Algorithm > Heap size

19 Tools and Tips – Monitoring Memory Java heap space > Monitoring: jstat > GC Activity

20 Tools and Tips – Monitoring Memory Each GC releases less memory than before Memory Leak indicator

21 Tools and Tips - Memory > Track down where is the problem – Heap dump (non intrusive)  Generate a dump file as large as the heap memory  Freezes application while dump is generated – Profilers (intrusive)  Need to reconfigure VM settings  Attach a client profiler to introspect

22 Tools and Tips - Memory > Heap dump > jmap -dump:live,format=b,file=dump23855_appserv1 23855 > -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=heapdump.hprof

23 Tools and Tips - Memory > Heap dump and profilers > Dump Analyzers and Profilers – IBM Heap Dump Analyzer – Eclipse Memory Analyzer – NetBeans Profiler

24 Tools and Tips - Memory > IBM Heap Analyzer

25 Tools and Tips - Memory > IBM Heap Analyzer

26 Tools and Tips - Memory > Eclipse Memory Analyzer

27 Tools and Tips - Memory > NetBeans Profiler 1 2

28 Tools and Tips - Memory > OutOfMemoryError – Look at log files – Search for hprof, hs_err or core files – Monitor memory usage  prstat, top, ps – Monitor GC activity  jstat, -verbose:gc, visualgc, jconsole,

29 Tools and Tips - Memory > OutOfMemoryError types – Java heap space – PermGen space – Out of swap space – unable to create new native thread – Requested array size exceeds VM limit – GC overhead limit exceeded Exception in thread quot;mainquot; java.lang.OutOfMemoryError: Java heap space at ConsumeHeap$BigObject.<init>(ConsumeHeap.java:22) at ConsumeHeap.main(ConsumeHeap.java:41)

30 Tools and Tips - Memory Java heap space > Causes – Low RAM memory – Small heap – Memory leak > Fix – More physical memory – Make heap larger – Fix memory leaks

31 Tools and Tips - Memory PermGen space > Causes – Low memory for permanent generation area – Classes on permanent generation are prevented to be collected  Classloader leak > Fix – Make permanent generation area, larger – Disable hot deployment or class reloading – for classloader leak

32 Tools and Tips - Memory Out of swap space > Cause – Often is caused by JNI code – No memory available to operating system > Fix – Reserve more memory to operating system – Lower the heap size

33 Tools and Tips - Memory Unable to create new native thread > Cause – Big stack size (-Xss) – Small memory available – Poor thread management > Fix – Make stack size smaller – Reserve more memory to operating system – Lower heap size – Better thread management  Java 5 thread pool

34 Tools and Tips - Memory Requested array size exceeds VM limit > Cause – Attempt to allocate an array that is larger than the heap size > Fix – Lower the array size – Make heap larger

35 Tools and Tips - Memory GC overhead limit exceeded > Cause – Too much time spent on GC (98%) and little heap (2%) to be free > Fix – Similar to “java heap space” – Tune GC behavior

36 Tools and Tips - Memory > VM Crashes – Search for hprof, hs_err or core files > Enable post morten diagnostics gcore -o <file> PID -XX:+HeapDumpOnOutOfMemoryError -XX:OnError > Generate thread and heap dumps to analyze it later

37 Tools and Tips - CPU Diagnosing CPU Issues

38 Tools and Tips - CPU > OS diagnostic tool – prstat, ps, top > Thread behavior – Thread dump, thread analyzer > GC Activity (again) – Monitor heap > Profiling

39 Tools and Tips - CPU Everybody waiting this guy ! > Thread dump and analyzer

40 Tools and Tips - CPU > Thread dump and analyzer

43 Tools and Tips - CPU > Profiler > CPU intensive task

44 Tools and Tips - CPU > Profiler > CPU intensive task, the caller class

45 Tools and Tips - CPU GC Activity Too much GC in short period of time, degrades performance > Fix – Adjust GC – Make heap larger

46 Tools and Tips – More tools More Tools to help diagnose issues... ...or to mess around your toolbox

47 Tools and Tips – More tools > Dtrace (Solaris, FreeBSD, Mac OSX) – Examine program behavior by reading points of instrumentation on java and solaris. > Sun Studio Tools (Solaris and Linux) – Graphical tools to help diagnose and debug memory and cpu issues > Profilers: Jprobe, Optimize It, YourKit, (commercial) > BEA JRockit Memory Leak Detector > JBoss Profiler (collect first, analyze later) > JXInsight (commercial - free dev. edition) – Monitor, diagnose and analysis of java systems >

48 Tools and Tips – More tools > CPU and Memory statistics – dstat, prstat, vmstat, mpstat > Networking – Wireshark (AKA ethereal), tcpdump, snoop, dig, netstat, > System call tracing – truss, strace, dtrace > Threading – pstack > Process – lsof, ps,

50 Application and System Performance Some general tips to improve overall performance

51 Application and System Performance > Application Servers – Properly configure pool resources  Threads pools are used everywhere  Connection pools for Http, JDBC, JMS, JCA, JMX, EJBs Monitor TCP connections and blocking connections to have a  general view to tune those parameters Many threads waiting on a single monitor, adjust the pool  – Http services  Enable resource cache  Configure timeout setting for http, database, session  Enable keep-alive  Put the data where it belongs Static data on webservers  Dynamic data on appserver  – Disable DNS lookup

52 Application and System Performance > Application Servers – Clustering  When session (HttpSession and SFSB) must synchronize themselves ?  Application must be designed to work under cluster  Make sure there are no-firewall between nodes  Hardware load balancers are faster  Large session size, can bring down the cluster  Memory replication is better – Classloader and Dynamic loading  Disable redeploy, autodeploy, auto discovery and JSP compilation

53 Application and System Performance > Java Concurrent Programming – Use thread pools – Lower VM stack size (-Xss) – Use util.concurrent classes  Collections  Atomic operations  Framework for multithread system – Synchronize the smallest possible code – Parallelize tasks on SMP systems  Be careful, context switching can be expensive

54 Application and System Performance > Java Runtime – Disable security manager at trusted sites – Disable class verifier (-Xnoverify) – Garbage Collector  Use Parallel GC when possible  Disable verbose:gc, prefer jstat 32 – 32 bit systems have address space restrictions of 2 bytes  Cannot configure -Xmx4g  If possible don't enable 64 bits (-d64)

55 Application and System Performance > Database – Have a database expert – For report systems  Configure a specific connection pool  Set a less restrictive transaction isolation level – Data cache  A cleaning policy is highly recommended – Don't use XA protocol, if possible – Use stored procedures for:  Data transformation between datasets  For large datasets – Pure JDBC for reporting or complex queries – Create indexes – Use optimistic concurrency scheme

56 Application and System Performance > I/O System – Get rid of all System.out – Use “if (log.isDebugEnabled())” before logging statements, to prevent string concatenation – Prefer java.io.Externalizable over standard serialization – Use buffers on I/O operations – On NIO systems  Be careful of allocation outside heap, use -XX:MaxDirectMemorySize  Decide which type of allocation to use  Consider FileChannel for copy or read operations

57 Application and System Performance > General Java Programming – Use Weak and Soft references – Bad hashCode and equals implementation can make your cache crazy > XML – Prefer a binary formato for communication protocol > Log management – Log levels for production and development systems – No debug messages for production systems, please – Don't log method names or package abbreviation

59 General Tips Why is the top management upset at stacktraces on the server ?

60 General Tips > Don't panic yourself into the crazy bandwagon > Try to have a good view of the overall computing system – Infrastructure, operating system, daemons, firewalls, application servers, configurations, what was working before > Be careful to trust the information sources > Don't prematurely tell the customer about the solution > Critical understanding of the affected services and importance to the customer > Get to know teams and respective leaders/managers > Confirm reports told by other people > Verify system settings

61 General Tips > Understand how to use the tools and its output > Don't depend on graphical consoles > Have access to the application's source code > Have a good decompiler (if the previous one fails) > When notifying the customer about the issue, bring him the fix – And have a happy customer

62 Questions ?

Claudio Miranda http://weblogs.java.net/blog/claudio claudio@claudius.com.br Summa Technologies http://www.summa-tech.com

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Tools and Tips to Diagnose Performance Issues

by Claudio Miranda on Jun 24, 2008

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Tools and Tips to Diagnose Performance Issues — Presentation Transcript