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

6
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
>

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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

11
AGENDA
> Where it all begins
> Tools and tips to diagnose problems
> Application and system performance
> General tips

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

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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

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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

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Tools and Tips
Diagnose Memory Issues

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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

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

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

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

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

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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

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

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

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Tools and Tips - Memory
> IBM Heap Analyzer

25
Tools and Tips - Memory
> IBM Heap Analyzer

26
Tools and Tips - Memory
> Eclipse Memory Analyzer

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Tools and Tips - Memory
> NetBeans Profiler
1
2

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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,

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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 \"main\" java.lang.OutOfMemoryError: Java heap space
at ConsumeHeap$BigObject.<init>(ConsumeHeap.java:22)
at ConsumeHeap.main(ConsumeHeap.java:41)

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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

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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

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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

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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

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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

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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

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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

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Tools and Tips - CPU
Diagnosing CPU Issues

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

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

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Tools and Tips - CPU
> Thread dump and analyzer

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Tools and Tips - CPU
> Thread dump and analyzer

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Tools and Tips - CPU
> Thread dump and analyzer

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Tools and Tips - CPU
> Profiler
> CPU intensive task

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

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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

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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
>

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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,

49
AGENDA
> Where it all begins
> Tools and tips to diagnose problems
> Application and system performance
> General tips

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

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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

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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

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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

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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
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– 32 bit systems have address space restrictions of 2 bytes
 Cannot configure -Xmx4g
 If possible don't enable 64 bits (-d64)

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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

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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

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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

58
AGENDA
> Where it all begins
> Tools and tips to diagnose problems
> Application and system performance
> General tips

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

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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

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Questions ?

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