{"id":964,"date":"2008-11-18T15:59:36","date_gmt":"2008-11-18T19:59:36","guid":{"rendered":"http:\/\/onlineappsdba.com\/index.php\/2008\/11\/18\/jvm-tuning-garbage-collection-in-oracle-apps-11i\/"},"modified":"2008-11-18T16:07:36","modified_gmt":"2008-11-18T20:07:36","slug":"jvm-tuning-garbage-collection-in-oracle-apps-11i","status":"publish","type":"post","link":"https:\/\/onlineappsdba.com\/index.php\/2008\/11\/18\/jvm-tuning-garbage-collection-in-oracle-apps-11i\/","title":{"rendered":"JVM Tuning (Garbage Collection) in Oracle Apps 11i"},"content":{"rendered":"

There are some good notes on JVM tuning from Mike Shaw<\/strong> on Steven Chan’s<\/strong> blog\u00a0 here<\/a> , here<\/a> and here<\/a> and some good\u00a0Metalink\u00a0notes<\/strong> at end of this post.
\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Important thing missing from all these notes (for some one like me who is new to Java) is basics of Garbage Collection<\/strong>, Generation<\/strong> and how to read GC output<\/strong>.
\nIn this post I’ll start with basics of JVM GC<\/strong> (Garbage Collection) and then in next post apply this theory for real time performance issues<\/strong> w.r.t. JVM (11i Java Virtual Machine) .<\/p>\n

Garbage<\/u> <\/strong>– Java object is considered garbage when it can no longer be reached from any pointer in the running program.<\/p>\n

Generations<\/strong><\/u> – Memory in JVM is managed in terms of generation i.e. Young generation<\/strong> and tenured generation<\/strong>. Memory pool holding object of different ages <\/strong>like young, tenured. If a particular generation fills up, garbage collection occurs.<\/p>\n

A. Young generation<\/u><\/strong> – Objects are initially allocated in Young generation (most of objects die here). When Young generation fills up, it causes Minor Garbage Collection<\/strong>. Any objects survived after Minor GC (Garbage Collection) are moved to Tenured Generation<\/strong>.\u00a0 Minor Garbage collection is\u00a0quick<\/strong> as compared to Full\/Major GC.<\/p>\n

B. Tenured generation<\/u><\/strong> – Surviving objects (from young generation) after minor garbage collection are moved to area called tenured generation, When tenured generation fills up it causes major collection (aka Full GC<\/strong> or Full Garbage Collection). Major collection is slow<\/strong> as it involves all live objects.<\/p>\n

Garbage Collection<\/strong><\/u> (GC) – is program which clears garbage(dead java objects). Garbage Collection work on fundamental principle that majority of java objects die young<\/strong> (quickly after arriving in JVM). There are two kind of Garbage Collection Minor Garbage Collection<\/strong> and Major Garbage Collection<\/strong> (aka Full GC)<\/p>\n

Example of Minor GC<\/strong> –\u00a0 3824.164: [GC<\/strong> 196725K->141181K(209864K), 0.3295949 secs]
\nExample of Minor GC<\/strong> –\u00a0 3841.051: [Full<\/strong> GC 150466K->87061K(217032K), 3.2626248 secs]<\/p>\n

Pauses<\/u><\/strong>: is the time when application becomes unresponsive because garbage collection is occurring.<\/p>\n

.<\/p>\n

Understanding JVM parameter for 11i<\/u><\/strong>
\nSizing the generation is very important in tuning JVM GC. Before jumping to Sizing generation (Young and Tenured)\u00a0lets look at default 11i JVM parameters<\/strong><\/p>\n

In context file<\/strong>($APPL_TOP\/ admin\/ $CONTEXT_NAME.xml) default entry for JVM is like<\/p>\n

<jvm_options oa_var=”s_jvm_options” osd=”Solaris”>-verbose:gc -Xmx512M -Xms128M -XX:MaxPermSize=128M -XX:NewRatio=2<\/strong>-XX:+PrintGCTimeStamps -XX:+UseTLAB <\/jvm_options><\/font><\/p>\n

1.<\/strong> Above line represents JVM (OACoreGroup<\/strong>) size in 11i
\n2.<\/strong> -Xms128M,<\/strong> means start with 128MB heap size
\n3.<\/strong> -Xmx512M<\/strong>, means grow JVM heap size upto max size<\/strong> of 512 MB
\n4. <\/strong>-XX:NewRatio=2 is to control young generation<\/strong> i.e. ratio between young and tenured generation is 1:2 (i.e. if size of young generation is 50 MB then size of tenured generation should be approx. 100MB)
\n5.<\/strong> -XX:MaxPermSize=128M<\/strong> limit the permanent generation<\/strong> to 128M (permanent generation is part\/area in tenured generation)
\n6. <\/strong>-XX:+UseTLAB represents to use thread-local object allocation<\/strong>
\n7. <\/strong>There are two more parameters (11i JVM uses default values) -XX:MinHeapFreeRatio=<minimum> & -XX:MaxHeapFreeRatio=<maximum> with default value of 40 & 70 resp. (for Solaris)<\/p>\n

If percentage of free space in generation falls below 40%, size of generation will expand and if percentage of free space exceeds 70%, the size of generation will shrunk.<\/font><\/p>\n

.
\nVarious type of Garbage Collector
\n<\/u><\/strong>From JDK 1.4.2 there are total 4 type of collectors<\/strong> (prior to 1.4.2 it was just one collector i.e. default<\/strong> collector)<\/p>\n

1. Default Collector<\/strong>: JDK prior to 1.4.2 uses default collector. If you don’t specify any parameter with JVM default is default collector<\/strong>.<\/p>\n

2. ThroughPut Collector<\/strong> : This collector uses parallel version<\/strong> of young generation collector but\u00a0Tenrured generation is collected in normal way. To set throughput collector use –XX:+UseParallelGC\u00a0<\/strong> so change<\/p>\n

<jvm_options oa_var=”s_jvm_options” osd=”Solaris”>-verbose:gc -Xmx512M -Xms128M -XX:MaxPermSize=128M -XX:NewRatio=2 -XX:+PrintGCTimeStamps -XX:+UseTLAB <\/jvm_options><\/font>
\nto
\n<jvm_options oa_var=”s_jvm_options” osd=”Solaris”>-verbose:gc -Xmx512M -Xms128M -XX:MaxPermSize=128M -XX:NewRatio=2 -XX:+PrintGCTimeStamps -XX:+UseTLAB -XX:+UseParallelGC<\/strong><\/jvm_options><\/font><\/p>\n

3. Concurrent Low Pause Collector<\/strong> : Concurrent Collector is used to collect tenured generation collection concurrently<\/strong> with execution of application. Parallel version of collector is used for young generation<\/font>. To set Concurrent Low Pause Collector use –XX:+UseConcMarkSweepGC<\/strong>
\nlike
\n<jvm_options oa_var=”s_jvm_options” osd=”Solaris”>-verbose:gc -Xmx512M -Xms128M -XX:MaxPermSize=128M -XX:NewRatio=2 -XX:+PrintGCTimeStamps -XX:+UseTLAB -XX:+UseConcMarkSweepGC<\/jvm_options><\/font><\/p>\n

4. Incremental low pause collector<\/strong> : This collector collects just portion of tenured generation<\/strong> at each minor garbage collection. To use Incremental low pause collector use
\n-Xincgc<\/strong><\/p>\n

If you are on JDK 1.4.2 with multi CPU try setting\u00a0Concurrent Low Pause Collector<\/strong>as Garbage Collector.
\n<\/font><\/p>\n

Thumb rule for Grabage Collection\/ JVM tuning w.r.t. 11i
\n<\/u>1.<\/strong>Stay on latest JVM\/JDK version where ever possible (latest certified with 11i is JRE 6, you should be at-least 1.4.2 and higher)
\n2.<\/strong> For OACoreGroup<\/strong> consider no more than 100 active users per JVM
\n3.<\/strong> There should NOT be more than 1 active JVM per CPU
\n4. <\/strong>Try to reduce GC (Garbage Collection) frequency (specially Major\/Full GC). Play\u00a0with various JVM parameters like (-Xmx, -Xms, -XX:MaxPermSize, -XX:NewRatio, -XX:+UseParallelGC\/ -XX:+UseConcMarkSweepGC<\/strong>)
\n5.<\/strong> If you are on JDK 1.4.2 with multiple CPU middle tier, use Concurrent Low Pause Garbage Collector<\/strong>\u00a0 by setting -XX:+UseConcMarkSweepGC with JVM
\n6.<\/strong> If you are using Oracle Configurator<\/strong>, assign dedicated JVM for configurator requests
\n7.<\/strong> Try setting JVM max size NOT<\/strong>greater than 1 GB, (use multiple JVM’s of 512MB or 1024 MB), this is to reduce GC time (more heap size means more time in GC<\/font>)
\n8. <\/strong>Minor GC should be occurring at interval long enough to allow many objects to die young (i.e. lot of objects should die between two minor GC).
\n9.<\/strong> Throughput (which is time NOT <\/strong>spent on GC) is inversely proportion to amount of memory. Higher the memory for JVM, more time for GC meaning low throughput.
\n10.<\/strong> Unless you have problems with pauses<\/strong> (time when application becomes unresponsive because garbage collection is occurring<\/font>), try granting as much memory as possible to VM (128 to 512 is good start and fine tune as per load testing results)
\n.<\/p>\n

How to find JDK version used by Apache\/Jserv (JVM) in 11i ?
\n<\/strong>
\nIn context file search for parameter like s_jdktop<\/strong><\/p>\n

<JDK_TOP oa_var=”s_jdktop”>\/oracle\/apps\/11i\/vis11icomn\/util\/java\/1.4\/j2sdk1.4.2_04<\/JDK_TOP><\/p>\n

Where is JVM log location in 11i ?<\/strong>
\n$IAS_ORACLE_HOME\/ Apache\/ Jserv\/ logs\/ jvm\/ OACoreGroup.0.stdout\u00a0 (GC output<\/strong>)
\n$IAS_ORACLE_HOME\/ Apache\/ Jserv\/ logs\/ jvm\/ OACoreGroup.0.stderr\u00a0 (JVM Error<\/strong>)<\/p>\n

.<\/p>\n

How to read\u00a0GC (JVM\u00a0stdout) file ?<\/strong><\/p>\n

Example of JVM out file to understand Garbage Collection in 11i<\/p>\n

3824.164: [GC 196725K->141181K(209864K), 0.3295949 secs]
\n3840.734: [GC 207741K->150466K(217032K), 0.3168890 secs]
\n3841.051: [Full<\/strong> GC 150466K->87061K(217032K), 3.2626248 secs]
\n3854.717: [GC 155413K->97857K(215568K), 0.2732267 secs]
\n3874.714: [GC 166209K->109946K(215568K), 0.3498301 secs]<\/font><\/p>\n

1.<\/strong> Line 1,2 4 and 5 are example of Minor Collection<\/strong>
\n2.<\/strong> Line 3 (Full GC<\/strong>) is example of Major Collection<\/strong>
\n3.<\/strong> First entry in each line is time in seconds<\/strong> since JVM started, To find out time between two GC (Garbage Collection) just subtract second entry from first i.e. (3840.734 – 3824.164 = 16.57 seconds)
\n4.<\/strong> 196725K->141181K in first line indicates combined size of live objects<\/strong> before and after Garbage Collection (GC)
\n5.<\/strong> (209864K) in first line in parenthesis, represents object after minor collection <\/strong>that aren’t necessarily alive but can’t be reclaimed<\/strong>, either because they are directly alive, or because they are referenced from objects in tenured generation.
\n6.<\/strong> 0.3295949 secs in first line represents time taken to run minor collection<\/strong>.
\n7. <\/strong>Full GC in line three represents Full Garbage Collection<\/strong> or Major Collection<\/p>\n

.\u00a0
\nReferences<\/u><\/strong><\/p>\n