Download Java Garbage Collection Tip or Technique Product(s): IBM Cognos 8

Tip or Technique
Java Garbage Collection
Product(s): IBM Cognos 8
Area of Interest: Performance
Java Garbage Collection
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Copyright
Copyright © 2008 Cognos ULC (formerly Cognos Incorporated). Cognos ULC is
an IBM Company. While every attempt has been made to ensure that the
information in this document is accurate and complete, some typographical errors
or technical inaccuracies may exist. Cognos does not accept responsibility for
any kind of loss resulting from the use of information contained in this document.
This document shows the publication date. The information contained in this
document is subject to change without notice. Any improvements or changes to
the information contained in this document will be documented in subsequent
editions. This document contains proprietary information of Cognos. All rights are
reserved. No part of this document may be copied, photocopied, reproduced,
stored in a retrieval system, transmitted in any form or by any means, or
translated into another language without the prior written consent of Cognos.
Cognos and the Cognos logo are trademarks of Cognos ULC (formerly Cognos
Incorporated) in the United States and/or other countries. IBM and the IBM logo
are trademarks of International Business Machines Corporation in the United
States, or other countries, or both. All other names are trademarks or registered
trademarks of their respective companies. Information about Cognos products
can be found at www.cognos.com
This document is maintained by the Best Practices, Product and Technology
team. You can send comments, suggestions, and additions to
[email protected] .
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Contents
1
INTRODUCTION ............................................................................................ 4
1.1
1.2
1.3
PURPOSE ................................................................................................................ 4
APPLICABILITY ......................................................................................................... 4
EXCLUSIONS AND EXCEPTIONS ..................................................................................... 4
2
JAVA COMMAND-LINE OPTIONS .................................................................. 5
2.1
2.2
2.3
SUN ...................................................................................................................... 5
IBM...................................................................................................................... 5
HP ....................................................................................................................... 5
3
STARTUP ....................................................................................................... 6
3.1
3.2
3.3
LIMITATIONS ........................................................................................................... 6
STARTUP.BAT ........................................................................................................... 6
COGBOOTSTRAPSERVICE ............................................................................................. 9
4
MONITORING GARBAGE COLLECTION ....................................................... 11
4.1
GCVIEWER FROM TAGTRAUM .................................................................................... 11
5
ADDITIONAL JAVA PARAMETERS ............................................................... 13
5.1
5.2
5.3
HTTP PROXY ........................................................................................................ 13
ORACLE JDBC TRACING ........................................................................................... 14
DB2 JDBC TRACING ............................................................................................... 14
6
REFERENCES ............................................................................................... 15
6.1
6.2
6.3
6.4
6.5
SUN .................................................................................................................... 15
IBM.................................................................................................................... 15
HP ..................................................................................................................... 15
TAGTRAUM INDUSTRIES ........................................................................................... 15
TOMCAT PERFORMANCE............................................................................................ 15
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1 Introduction
1.1
Purpose
The allocation of Heap memory is one of the few tuneable parameters for a
Servlet Engine. Both excessive and insufficient Heap can cause performance
degradation due to Garbage Collection.
This document offers guidance on how to capture and observe the use of Heap
memory by Java for IBM Cognos 8 or IBM Cognos ReportNet.
1.2
Applicability
Instructions are provided only for integration with the Apache Tomcat servlet
engine embedded with the IBM Cognos products. When using an alternate
Application Server similar steps will be necessary but may be applied using that
product's Administrative User Interface.
1.3
Exclusions and Exceptions
Instructions are appropriate for all versions of IBM Cognos 8 and IBM Cognos
Report Net only when using Java 1.4.x or higher. The Java command-line
parameters indicated are not all supported by Java 1.3.x.
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2 Java Command-line options
We list here only the parameters which affect Garbage Collection logging. There
are many more supported and unsupported parameters which are not directly
relevant.
2.1
Sun
-verbose:gc
Prints out information about garbage collections. The default destination
is StdOut, so to redirect the same information to a file, use –
Xloggc:<file>
Example:
[GC 325407K->83000K(776768K), 0.2300771 secs]
[GC 325816K->83372K(776768K), 0.2454258 secs]
[Full GC 267628K->83769K(776768K), 1.8479984 secs]
-Xloggc:<filename>
Prints information about garbage collections to the specified file.
-XX:+PrintGCDetails
Instructs the VM to be more verbose when printing out garbage collecion
data. Specifically it does not only tell you that there was a collection, but
also what impact it had on the different generations. This flag is very
useful when tuning generation sizes.
2.2
IBM
-verbose:gc
Prints out information about garbage collections to standard out.
-Xverbosegclog:<filename[,X,Y]>
Prints out information about garbage collections to a file. If the integers X
and Y are specified, the output is redirected to X files each containing
output from Y GC cycles.
2.3
HP
-Xverbosegc[:help]|[0|1][:file=[stdout|stderr|<filename>]]
:help prints this message.
0|1 controls the printing of heap information:
0 Print after every Old Generation GC or Full GC
1 (default) Print after every Scavenge and Old Generation GC or Full GC
:file=[stdout|stderr|<filename>] specifies output file
stderr (default) directs output to standard error stream
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stdout
directs output to standard output stream
<filename> file to which the output will be written
3 Startup
3.1
Limitations
Java applications scale "out" better than "up". That is, performance is better by
distributing components of an application across many moderate sized Servlet
Containers rather than a monolithic instance. Each Servlet Container represents
one invocation of Java, and hence may also bind to a distinct CPU.
The IBM Cognos 8 application uses Java Native Methods for interaction with
external Security Namespaces, and for some Cryptographic functions. These are
32bit libraries, so a 32bit JRE is required (a 64bit JRE cannot load 32bit JNI
libraries).
A 32bit application can address a very finite amount of RAM. If the application
attempts to allocate more RAM than it can address then the Operating System
will terminate the application.
You will notice that even if Maximum Java Heap is 768MB (recommended), you
may observe that the total memory utilisation by the Java process exceeds 1GB.
This additional utilisation is Java itself plus JNI.
Java itself also needs some memory for its own operation. The sum of Java
working memory, maximum Heap, and JNI must not exceed addressable
memory. If the JNI is unable to allocate memory for eg User Session Information
[in the CAM subcomponent of the Content Manager] then Java may be
terminated. JNI memory is not subject to Garbage Collection, as that memory is
managed entirely by the JNI libraries that extend Java.
Problems have been observed allocating Java Heap > 1152MB on Windows.
IBM Cognos recommend:
Heap(Windows) < 1152MB
Java + Heap + JNI < 2GB
IBM Cognos further recommends that you do NOT assign the Initial (-Xms) and
Maximum (-Xmx) Heap to the same values as this practice degrades performance
of the garbage collector.
3.2
startup.bat
startup.bat (or startup.sh on Unix) is located at "c8_location/bin/startup.bat".
This is not an IBM Cognos-supported tool for starting the IBM Cognos-embedded
Tomcat but may be useful while debugging an errant installation, or if unable to
create the Service in Windows.
The startup.bat constructs a Java Command Line which directly invokes Tomcat.
It does not start any Service, and particularly does not start the IBM Cognos
watchdog process "cogbootstrapservice" which is normally used to ensure that
Tomcat is automatically restarted after any unexpected failure.
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The parameters indicated in startup.bat assume a Sun JRE. If using an IBM JRE
then CATALINA_OPTS must be modified.
@rem Copyright (C) 2006 Cognos Incorporated. All rights reserved.
@rem Cognos (R) is a trademark of Cognos Incorporated.
@echo off
setlocal
set CATALINA_HOME=..\tomcat4.1.27
if "%JAVA_HOME%" == "" set JAVA_HOME=..\bin\jre\1.4.2
set CATALINA_TMPDIR=..\temp
IF NOT EXIST %CATALINA_TMPDIR% md %CATALINA_TMPDIR%
rem uncomment next line to run tomcat with debug settings,
rem so you can attach a debugger.
rem set DEBUG_OPTS=-Xdebug -Xnoagent Xrunjdwp:transport=dt_socket,address=9091,server=y,suspend=y Djava.compiler=NONE
rem
set
set
set
uncomment next lines to
DEBUG_OPTS=%DEBUG_OPTS%
DEBUG_OPTS=%DEBUG_OPTS%
DEBUG_OPTS=%DEBUG_OPTS%
enable GarbageCollection logging
-Xincgc
-Xloggc:../logs/gc.log
-XX:+PrintGCDetails
rem "for machines with 1GB RAM"
set CATALINA_OPTS=-Xmx768m -XX:MaxNewSize=384m -XX:NewSize=192m XX:MaxPermSize=128m %DEBUG_OPTS%
rem "for machines with 2GB RAM"
rem set CATALINA_OPTS=-Xmx1152m -XX:MaxNewSize=576m -XX:NewSize=288m XX:MaxPermSize=128m %DEBUG_OPTS%
rem "for machines with 3GB RAM"
rem set CATALINA_OPTS=-Xmx1536m -XX:MaxNewSize=768m -XX:NewSize=384m XX:MaxPermSize=128m %DEBUG_OPTS%
call "%CATALINA_HOME%\bin\catalina"
run
%*
endlocal
As Windows cannot manage a Heap larger than 1152MB then the section "for
machines with 3GB RAM" above should not be used.
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In the last line where "catalina" is invoked, the parameter "run" instructs Tomcat
to run in a foreground window –useful for observing TCP or JDBC errors. The
default is "start" which runs Tomcat in a background window.
To stop Tomcat, either terminate the Command Window or invoke
"shutdown.bat".
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3.3
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cogbootstrapservice
The Windows Service "cogbootstrapservice" uses the information in
"c8_location/bin/bootstrap_win32.xml" and
"c8_location/configuration/cogstartup.xml" to construct a Java Command-line
which invokes Tomcat.
Similarly, the startup procedure "cogconfig.sh –s" on Unix uses the information in
"c8_location/bin/bootstrap_<OS>.xml" [where <OS> is "aix", etc] to construct
the Java Command-line.
If using an alternate Application Server (eg IBM WebSphere) then this file is not
used.
<process name="catalina">
<start>
<spawn sync="0" wait_time="5">
<path quoteAsParam="true">${java_home}/bin/java.exe</path>
<param>-Xrs</param>
<param>-Xmx${dispatcherMaxMemory}m</param>
<param condName="${java_vendor}" condValue="Sun">XX:MaxNewSize=${dispatcherMaxMemoryBy2}m</param>
<param condName="${java_vendor}" condValue="Sun">XX:NewSize=${dispatcherMaxMemoryBy4}m</param>
<param condName="${java_vendor}" condValue="Sun">XX:MaxPermSize=128m</param>
<!-- uncomment these for debug -->
<!— (useless without Source Code)
<param>-Xdebug</param>
<param>-Xnoagent</param>
<param>Xrunjdwp:transport=dt_socket,address=9091,server=y,suspend=y</param>
<param>-Djava.compiler=NONE</param>
-->
<!-- end debug params -->
<!-- uncomment these for garbage collection logging -->
<!-< param condName="${java_vendor}" condValue="Sun">-Xincgc</param>
< param condName="${java_vendor}" condValue="Sun">Xloggc:${install_path}/logs/gc.log</param>
< param condName="${java_vendor}" condValue="Sun">XX:+PrintGCDetails</param>
< param condName="${java_vendor}" condValue="IBM">verbose:gc</param>
< param condName="${java_vendor}" condValue="IBM">Xverbosegclog:${install_path}/logs/gc.log</param>
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-->
<!-- end gc -->
<param>-cp</param>
<param>"${install_path}/tomcat4.1.27/bin/bootstrap.jar;${java_home}/lib/
tools.jar"</param>
<param>"-Dcatalina.base=${install_path}/tomcat4.1.27"</param>
<param>"-Dcatalina.home=${install_path}/tomcat4.1.27"</param>
<param>"-Djava.io.tmpdir=${temp}"</param>
<param>org.apache.catalina.startup.Bootstrap</param>
<param>start</param>
</spawn>
</start>
… … …
Currently (IBM Cognos 8.1 mr2) the condValue element above supports only Sun
and IBM. If using HP's JVM then merely use the following fragment to capture
Garbage Collection logs:
<param>-Xverbosegc:file=${install_path}/logs/gc.log</param>
The ClassPath ("-cp") specifies only the JAR files necessary to start Tomcat itself.
Tomcat uses the information in "server.xml" and each deployed application's
Deployment Descriptor "web.xml" to locate and load the JAR files of each
Servlet.
See http://tomcat.apache.org/tomcat-4.1-doc/config/index.html for more details.
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4 Monitoring Garbage Collection
4.1
GCViewer from TagTraum
See http://www.tagtraum.com/gcviewer.html
This tool allows you to retrieve Garbage Collection Logs directly from a URL as
well as from a file. If you assign an Alias to the "c8_location/logs" or configure
the Garbage Collection logs to be written to "c8_location/webcontent/gc.log"
then you can observe the Heap utilisation remotely, eg:
• if written to "c8_location/logs/gc.log" and is assigned to an alias then
http://webserver:80/cognos8/logs/gc.log
• if written to "c8_location/webcontent/gc.log" then
http://webserver:80/cognos8/gc.log
• if written to "c8_location/webapps/p2pd/gc.log" (IBM Cognos-supplied
Tomcat only) then http://appserver:9300/p2pd/gc.log
In the sample graph above you can see the Actual heap utilisation in the
sawtooth Blue line. Each "tooth" represents a garbage collection. The Red
shading shows the Maximum heap utilisation over time.
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You need to size the "-Xmx" Java parameter to represent slightly more than the
observed Maximum Utilisation. Cognos recommends 768MB in most cases, and
that you should distribute Cognos components over multiple Java Servlet
Containers rather than creating a monolithic container.
Additional Java parameters may be used to manage the size of the different
generation portions of the Heap which are GC'd differently.
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5 Additional Java Parameters
5.1
HTTP Proxy
If operating IBM Cognos 8 in a network that requires a Proxy Server to access
the Internet, then IBM Cognos 8 may be unable to access RSS sites.
You can modify the Java Command-line to specify HTTP Proxy settings so that
the RSS Client within the Presentation Service of the IBM Cognos 8 servlet is able
to retrieve the RSS content.
Example RSS feeds that you could add to a Page in IBM Cognos 8:
• IBM Cognos http://www.cognos.com/rss/
o SupportLink http://support.cognos.com/en/gcs/rss/supportlink.xml
o News Releases
http://www.cognos.com/rss/cognosnewsreleases.xml
• BBC World News
http://newsrss.bbc.co.uk/rss/newsonline_uk_edition/front_page/rss.xml
• New York Times International News
http://www.nytimes.com/services/xml/rss/nyt/International.xml
Add the bolded fragment below into the <start> section of
"c8_location/bin/bootstrap_<OS>.xml" amongst the <param> entries:
<!-- uncomment these to enable Proxy access to Internet -->
<!-<param>-Dhttp.proxyHost=YourProxyServer</param>
<param>-Dhttp.proxyPort=3128</param>
<param>-Dhttp.nonProxyHosts=localhost</param>
-->
<!-<param>-Dhttp.proxyUser=username</param>
<param>-Dhttp.proxyPassword=password</param>
-->
<!-- end proxy -->
<param>"-cp"</param>
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5.2
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Oracle JDBC Tracing
If experiencing problems connecting from the Content Manager to an Oracle
Content Store, or from the Scheduling & Delivery Service to the Notification
Store, or from Logging Service to an Oracle Audit database then you may need
to enable JDBC Tracing.
Refer to
http://www.oracle.com/technology/tech/java/sqlj_jdbc/htdocs/jdbc_faq.htm#32_
00
You must replace the "classes12.jar" with the debugging-enabled version
"classes12_g.jar", or "ojdbc14.jar" with "ojdbc14_g.jar", and must add the
bolded fragment below into the <start> section of
"c8_location/bin/bootstrap_<OS>.xml" amongst the <param> entries:
<!-- uncomment these to enable Oracle JDBC tracing -->
<!-<param>-Doracle.jdbc.Trace=true</param>
<param>-Doracle.jdbc.LogFile=${install_path}/logs/ojdbc.log</param>
-->
<!-- end Oracle trace -->
<param>"-cp"</param>
Note that issues involving interaction between Reports and Oracle are not
captured by these logs. The Report Servers use Oracle Native connectivity (OCI),
not JDBC.
5.3
DB2 JDBC Tracing
The DB2 JDBC driver "db2java.jar" is a JDBC Type-II driver which uses the native
DB2 Client libraries to connect to the database.
JDBC tracing is enabled in the client configuration files, and does not require
changes to the Java command-line.
Refer:
• http://www128.ibm.com/developerworks/db2/library/techarticle/0205bargas/0205bar
gas.html
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6 References
6.1
Sun
Java Tuning Whitepaper
http://java.sun.com/performance/reference/whitepapers/tuning.html
Tuning Garbage Collection with the 1.4.2 Java Virtual Machine
http://java.sun.com/docs/hotspot/gc1.4.2/index.html
VM flags
http://www.tagtraum.com/gcviewer-vmflags.html#sun
6.2
IBM
IBM JVM Garbage Collection and Storage Allocation techniques
ftp://www6.software.ibm.com/software/developer/jdk/diagnosis/GCandMemory042005.pdf
Tivoli Performance Viewer
http://publib.boulder.ibm.com/infocenter/wasinfo/v6r0/index.jsp?topic=/com.ibm
.websphere.nd.doc/info/ae/ae/cprf_tpv.html
VM flags
http://www.tagtraum.com/gcviewer-vmflags.html#ibm
6.3
HP
HPjtune
http://www.hp.com/products1/unix/java/java2/hpjtune/index.html
VM flags
http://www.hp.com/products1/unix/java/infolibrary/prog_guide/xverbosegc_1-41.html?jumpid=reg_R1002_USEN
6.4
TagTraum Industries
http://www.tagtraum.com/gcviewer.html
6.5
Tomcat Performance
http://tomcat.apache.org/articles/performance.pdf
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