The application server is a Java based process and requires a Java virtual machine (JVM) environment to run and support the Java applications running on the application server. You can configure the Java runtime environment to tune performance and system resource usage. This topic applies to the IBM Technology for Java Virtual Machine. Refer to the topic Tuning the Classic JVM if you are using the IBM Developer Kit for Java that is provided with the i5/OS product.
Issue the java –fullversion command
from within your application server app_server_root/java/bin directory. In response to this command, the application server writes information
about the JVM, including the JVM provider information, into the SystemOut.log file.
Use the enablejvm command, if you want to
enable your application server profile to use a different JVM
On
the z/OS platform there is a JVM in both the controller and servant. This
information applies to the JVM in the servant. Usually the JVM in the controller
does not need to be tuned.
A Java runtime environment provides the execution environment for Java based applications and servers such as WebSphere Application Server. Therefore the Java configuration plays a significant role in determining performance and system resource consumption for the product, and the applications that you are running.
The IBM Java 5.0 and newer versions include major improvements in virtual machine technology to provide significant performance and serviceability enhancements over IBM's earlier Java execution technology. Refer to the Web site http://www.ibm.com/software/webservers/appserv/was/performance.html for more information about this new technology.
Even though JVM tuning is dependent on the JVM provider you use, there are some general tuning concepts that apply to all JVMs. These general concepts include:
The following steps provide specific instructions on how to perform the following types of tuning for each JVM. The steps do not have to be performed in any specific order.
In the General Properties section of the Configuration Tab, ensure that Disable JIT is not selected.
In some environments, such as a development environment, it is more important to optimize the startup performance of your application server rather than the runtime performance. In other environments, it is more important to optimize the runtime performance. By default, IBM virtual machines for Java are optimized for runtime performance, while HotSpot based JVMs are optimized for startup performance.
The Java Just-In-Time (JIT) compiler has a big impact on whether startup or runtime performance is optimized. The initial optimization level that the compiler uses influences the length of time it takes to compile a class method, and the length of time it takes to start the server. For faster startups, you should reduce the initial optimization level that the compiler uses. However if you reduce the initial optimization level, the runtime performance of your applications might be degraded because the class methods are now compiled at a lower optimization level.
This setting influences how the IBM virtual machine for Java uses a lower optimization level for class method compiles. A lower optimization level provides for faster server startups, but lowers runtime performance. If this parameter is not specified, the IBM virtual machine for Java defaults to starting with a high initial optimization level for compiles, which results in faster runtime performance, but slower server starts.
Default: | High initial compiler optimization level |
Recommended: | High initial compiler optimization level |
Usage: | -Xquickstart provides faster server startup. |
-Xquickstart -Xverify:none
HotSpot based JVMs initially compile class
methods with a low optimization level. Use this JVM option to change that
behavior:
In certain error conditions, multiple application server threads might fail and the JVM requests a TDUMP for each of those threads. This situation can cause a large number of TDUMPs to be taken concurrently leading to other problems, such. as a shortage of auxiliary storage. You can use the JAVA_DUMP_OPTS environment variable to indicate the number of dumps that you want the JVM to produce in certain situations. However it does not affect the number of TDUMPS that are generated because of com.ibm.jvm.Dump.SystemDump() calls from applications that are running on the application server.
JAVA_DUMP_OPTS=ONANYSIGNAL(JAVADUMP[3],SYSDUMP[1]),ONINTERRUPT(NONE)
See the IBM Developer Kit Diagnostics Guide for more information on using the JAVA_DUMP_OPTS environment variable.
The
Java heap parameters influence the behavior of garbage collection. Increasing
the heap size supports more object creation. Because a large heap takes
longer to fill, the application runs longer before a garbage collection occurs.
However, a larger heap also takes longer to compact and causes garbage collection
to take longer.
The heap size settings control garbage
collection in the JVM that is provide with i5/OS. The initial heap size is
a threshold that triggers new garbage collection cycles. For example, if the
initial heap size is 10 MB, a new collection cycle is triggered as soon as
the JVM detects that since the last collection cycle, 10 MB are allocated.
Smaller heap sizes result in more frequent
garbage collections than larger heap sizes. If the maximum heap size is reached,
the garbage collector stops operating asynchronously, and user threads are
forced to wait for collection cycles to complete.
The
maximum heap size can affect application performance. The maximum heap size
specifies the maximum amount of object space the garbage collected heap can
consume. If the maximum heap size is too small, performance might degrade
significantly, or the application might receive out of memory errors when
the maximum heap size is reached.
The IBM Developer Kit and Runtime Environment, Java2 Technology Edition, Version 5.0 Diagnostics Guide, that is available on the developerWorks Web site, provides additional information on tuning the heap size.
Java
Heap information is contained in SMF records and can be viewed dynamically
using the console command DISPLAY,JVMHEAP.
To use the administrative console to configure the heap size:
You can also specify values for both fields if you need to adjust both settings.
The Initial heap size setting specifies, in megabytes, the amount of storage that is allocated for the JVM heap when the JVM starts. The Maximum heap size setting specifies, in megabytes, the maximum amount of storage that can be allocated to the JVM heap. Both of these settings have a significant effect on performance.
When tuning a production system where the working set
size of the Java application is not understood, a good starting value for
the initial heap size is 25% of the maximum heap size. The JVM then tries
to adapt the size of the heap to the working set size of the application.
The illustration represents three CPU profiles, each running a fixed workload with varying Java heap settings. In the middle profile, the initial and maximum heap sizes are set to 128MB. Four garbage collections occur. The total time in garbage collection is about 15% of the total run. When the heap parameters are doubled to 256MB, as in the top profile, the length of the work time increases between garbage collections. Only three garbage collections occur, but the length of each garbage collection is also increased. In the third profile, the heap size is reduced to 64MB and exhibits the opposite effect. With a smaller heap size, both the time between garbage collections and the time for each garbage collection are shorter. For all three configurations, the total time in garbage collection is approximately 15%. This example illustrates an important concept about the Java heap and its relationship to object utilization. There is always a cost for garbage collection in Java applications.
If
the heap free space settles at 85% or more, consider decreasing the maximum
heap size values because the application server and the application are under-utilizing
the memory allocated for heap.
If
you have servers configured to run in 64-bit mode, you can specify a JVM maximum
heap size for those servers that is significantly larger than the default
setting. For example, you can specify an initial maximum heap size of 1844m
for the controller and the servant if the server is configured to run in 64-bit
mode.
You can also use the following command line parameters to adjust these settings. These parameters apply to all supported JVMs and are used to adjust the minimum and maximum heap size for each application server or application server instance.
This setting controls the initial size of the Java heap. Properly tuning this parameter reduces the overhead of garbage collection, which improves server response time and throughput. For some applications, the default setting for this option might be too low, which causes a high number of minor garbage collections.
Default: | 50MB. This default value applies for both 31-bit and 64-bit configurations. |
Recommended: | Workload specific, but higher than the default. |
Usage: | -Xms256m sets the initial heap size to 256 megabytes. |
This setting controls the maximum size of the Java heap. Increasing this parameter increases the memory available to the application server, and reduces the frequency of garbage collection. Increasing this setting can improve server response time and throughput. However, increasing this setting also increases the duration of a garbage collection when it does occur. This setting should never be increased above the system memory available for the application server instance. Increasing the setting above the available system memory can cause system paging and a significant decrease in performance.
Default: | 256MB. This default value applies for both 31-bit and 64-bit configurations. |
Recommended: | Workload specific, but higher than the default, depending on the amount of available physical memory. |
Usage: | -Xmx512m sets the maximum heap size to 512 megabytes. |
This setting is used with the IBM virtual machine for Java to allocate the heap when using large pages (16MB). However, if you use this setting your operating system must be configured to support large pages. Using large pages can reduce the CPU overhead needed to keep track of heap memory, and might also allow the creation of a larger heap.
See Tuning operating systems for more information about tuning your operating system.
This setting can be used with the IBM virtual machine for Java to allocate the heap using a 64 kilobyte page size (medium pages). Using this virtual memory page size for the memory that an application requires can improves the performance and throughput of the application because of hardware efficiencies that are associated with a larger page size.
To support a 64KB page size, in the administrative console, click Servers > Application servers > server_name > Process Definition > Environment Entries > New, and then specify LDR_CNTRL in the Name field and DATAPSIZE=64K@TEXTPSIZE=64K@STACKPSIZE=64K in the Value field
AIX has rich support around 64KB pages, and 64KB pages are intended to be general purpose. 64KB pages are very easy to use, and it is expected that many applications will see performance benefits when using 64KB pages rather than the default 4KB pages. This setting can be changed without changing the operating system configuration.
Default: | 4KB |
Recommended: | -Xlp64k enables the 64KB page size support. Note: POWER5+ systems,
AIX 5L Version 5.3 with the 5300-04 Recommended Maintenance Package supports
a new 64KB page size when running the 64-bit kernel.
|
You can use the Tivoli Performance Viewer to check You
can use the Tivoli Performance Viewer to observe the counters for the JVM
runtime. This information indicates whether the application is overusing objects.
Refer to the topic Enabling the Java virtual machine profiler data for
more information JVMPI counters.
You can use the Tivoli Performance Viewer to check
if the application is overusing objects, by observing the counters for the
JVM runtime. You have to set the -XrunpmiJvmpiProfiler command line
option, as well as the JVM module maximum level in order to enable the Java
virtual machine profiler interface (JVMPI) counters.
The
best result for the average time between garbage collections is at least 5-6
times the average duration of a single garbage collection. If you do not achieve
this number, the application is spending more than 15 percent of its time
in garbage collection.
You can check if the application
is overusing objects, by observing the counters for the JVM runtime. You have
to set the -XrunpmiJvmpiProfiler command line option, as well as the
JVM module maximum level in order to enable the Java virtual machine profiler
interface (JVMPI) counters. The best result for the average time between garbage
collections is at least 5-6 times the average duration of a single garbage
collection. If you do not achieve this number, the application is spending
more than 15% of its time in garbage collection.
If the information indicates a garbage collection bottleneck, there are two ways to clear the bottleneck. The most cost-effective way to optimize the application is to implement object caches and pools. Use a Java profiler to determine which objects to target. If you can not optimize the application, adding memory, processors and clones might help. Additional memory allows each clone to maintain a reasonable heap size. Additional processors allow the clones to run in parallel.
Memory leaks in the Java language are a dangerous contributor to garbage collection bottlenecks. Memory leaks are more damaging than memory overuse, because a memory leak ultimately leads to system instability. Over time, garbage collection occurs more frequently until the heap is exhausted and the Java code fails with a fatal out-of-memory exception. Memory leaks occur when an unused object has references that are never freed. Memory leaks most commonly occur in collection classes, such as Hashtable because the table always has a reference to the object, even after real references are deleted.
High workload often causes applications to crash immediately after deployment in the production environment. This is especially true for leaking applications where the high workload accelerates the magnification of the leakage and a memory allocation failure occurs.
Memory leak problems can manifest only after a period of time, therefore, memory leaks are found easily during long-running tests. Short running tests can lead to false alarms. It is sometimes difficult to know when a memory leak is occurring in the Java language, especially when memory usage has seemingly increased either abruptly or monotonically in a given period of time. The reason it is hard to detect a memory leak is that these kinds of increases can be valid or might be the intention of the developer. You can learn how to differentiate the delayed use of objects from completely unused objects by running applications for a longer period of time. Long-running application testing gives you higher confidence for whether the delayed use of objects is actually occurring.
In many cases, memory leak problems occur by successive repetitions of the same test case. The goal of memory leak testing is to establish a big gap between unusable memory and used memory in terms of their relative sizes. By repeating the same scenario over and over again, the gap is multiplied in a very progressive way. This testing helps if the number of leaks caused by the execution of a test case is so minimal that it is hardly noticeable in one run.
You can use repetitive tests at the system level or module level. The advantage with modular testing is better control. When a module is designed to keep the private module without creating external side effects such as memory usage, testing for memory leaks is easier. First, the memory usage before running the module is recorded. Then, a fixed set of test cases are run repeatedly. At the end of the test run, the current memory usage is recorded and checked for significant changes. Remember, garbage collection must be suggested when recording the actual memory usage by inserting System.gc() in the module where you want garbage collection to occur, or using a profiling tool, to force the event to occur.
Some memory leak problems can occur only when there are several threads running in the application. Unfortunately, synchronization points are very susceptible to memory leaks because of the added complication in the program logic. Careless programming can lead to kept or unreleased references. The incident of memory leaks is often facilitated or accelerated by increased concurrency in the system. The most common way to increase concurrency is to increase the number of clients in the test driver.
You can use the Tivoli Performance Viewer to help
find memory leaks.
Also, look at the difference between the
number of objects allocated and the number of objects freed. If the gap between
the two increases over time, there is a memory leak.
Heap consumption indicating a possible leak during a heavy workload (the application server is consistently near 100% CPU utilization), yet appearing to recover during a subsequent lighter or near-idle workload, is an indication of heap fragmentation. Heap fragmentation can occur when the JVM can free sufficient objects to satisfy memory allocation requests during garbage collection cycles, but the JVM does not have the time to compact small free memory areas in the heap to larger contiguous spaces.
Another form of heap fragmentation occurs when small objects (less than 512 bytes) are freed. The objects are freed, but the storage is not recovered, resulting in memory fragmentation until a heap compaction has been run.
Heap fragmentation can be reduced
by forcing compactions to occur, but there is a performance penalty for doing
this. Use the Java -X command to see the list of memory options.
The Java virtual
machine (JVM) uses a parallel garbage collector to fully exploit an SMP during
most garbage collection cycles. The HotSpot based JVMs have a single-threaded
garbage collector.
Examining Java garbage collection gives insight to how the application is utilizing memory. Garbage collection is a Java strength. By taking the burden of memory management away from the application writer, Java applications are more robust than applications written in languages that do not provide garbage collection. This robustness applies as long as the application is not abusing objects. Garbage collection normally consumes from 5% to 20% of total execution time of a properly functioning application. If not managed, garbage collection is one of the biggest bottlenecks for an application.
Monitoring garbage collection during the execution of a fixed workload, enables you to gain insight as to whether the application is over-utilizing objects. Garbage collection can even detect the presence of memory leaks.
You can use JVM settings to configure the type and behavior of garbage collection. When the JVM cannot allocate an object from the current heap because of lack of contiguous space, the garbage collector is invoked to reclaim memory from Java objects that are no longer being used. Each JVM vendor provides unique garbage collector policies and tuning parameters.
You can use the Verbose garbage collection setting in the administrative console to enable garbage collection monitoring. The output from this setting includes class garbage collection statistics. The format of the generated report is not standardized between different JVMs or release levels.
To
ensure meaningful statistics, run a fixed workload until the application state
is steady. It usually takes several minutes to reach a steady state.
You can also use object statistics in the Tivoli Performance
Viewer to monitor garbage collection statistics.
To adjust your JVM garbage collection settings:
For more information about the –X options for the different JVM garbage collectors refer to the following:
Use
the Java -X option to view a list of memory options.
Default: | optthruput |
Recommended: | optthruput |
Usage: | Xgcpolicy:optthruput sets the garbage collection to optthruput |
Setting gcpolicy to optthruput disables concurrent mark. You should get the best throughput results when you use the optthruput policy unless you are experiencing erratic application response times, which is an indication that you might have pause time problems
Setting gcpolicy to optavgpause enables concurrent mark with its default values. This setting alleviates erratic application response times that normal garbage collection causes. However, this option might decrease overall throughput.
By default, the JVM unloads a class from memory whenever there are no live instances of that class left. Therefore, class unloading can degrade performance.
You can use the -Xnoclassgc argument to disable class garbage collection so that your applications can reuse classes more easily. Turning off class garbage collection eliminates the overhead of loading and unloading the same class multiple times.
Default: | Class garbage collection is enabled. |
Recommended: |
|
Usage: | Xnoclassgc disables class garbage collection. |
On the Solaris platform, an application server runs on the Java HotSpot VM rather than the IBM virtual machine for Java. It is important to use the correct tuning parameters with the Sun JVM in order to utilize its performance optimizing features.
The Java HotSpot VM relies on generational garbage collection to achieve optimum performance. The following command line parameters are useful for tuning garbage collection.
The Java heap is divided into a section for old (long lived) objects and a section for young objects. The section for young objects is further subdivided into the section where new objects are allocated, called eden, and the section where new objects that are still in use survive their first few garbage collections before being promoted to old objects, called survivor space. Survivor ratio is the ratio of eden to survivor space in the young object section of the heap. Increasing this setting optimizes the JVM for applications with high object creation and low object preservation. Because WebSphere Application Server instances generate more medium and long lived objects than other application servers, this setting should be lowered from the default.
Default: | 32 |
Recommended: | 16 |
Usage: | -XX:SurvivorRatio=16 |
The section of the heap reserved for the permanent generation holds all of the reflective data for the JVM. This size should be increased to optimize the performance of applications that dynamically load and unload a lot of classes. Setting this to a value of 128 megabytes eliminates the overhead of increasing this part of the heap.
Recommended: | 128m |
Usage: | XX:PermSize=128m sets perm size to 128 megabytes. |
This setting controls how much space the young generation is allowed to consume on the heap. Properly tuning this parameter can reduce the overhead of garbage collection, improving server response time and throughput. The default setting for this is typically too low, resulting in a high number of minor garbage collections. Setting this setting too high can cause the JVM to only perform major (or full) garbage collections. These usually take several seconds and are extremely detrimental to the overall performance of your server. You must keep this setting below half of the overall heap size to avoid this situation.
Default: | 2228224 bytes |
Recommended: | Approximately 1/4 of the total heap size |
Usage: | -Xmn256m sets the size to 256 megabytes. |
By default the JVM unloads a class from memory when there are no live instances of that class left, but this can degrade performance. Turning off class garbage collection eliminates the overhead of loading and unloading the same class multiple times.
If a class is no longer needed, the space that it occupies on the heap is normally used for the creation of new objects. However, if you have an application that handles requests by creating a new instance of a class and if requests for that application come in at random times, it is possible that when the previous requester is finished, the normal class garbage collection will clean up this class by freeing the heap space it occupied, only to have to re-instantiate the class when the next request comes along. In this situation you might want to use this option to disable the garbage collection of classes.
Default: | Class garbage collection is enabled. |
Recommended: | Class garbage collection is disabled. |
Usage: | Xnoclassgc disables class garbage collection. |
For additional information on tuning the Java HotSpot virtual machine, see Performance Documentation for the Java HotSpot VM.
The HP virtual machine for Java relies on generational garbage collection to achieve optimum performance. The following command line parameters are useful for tuning garbage collection.
This setting allows the JVM to automatically and aggressively tune the Java heap. If you are passing multiple arguments to the JVM, you should specify this argument first because it can cause some of the other arguments, such as the heap size settings, to be overridden. The aggressive tuning algorithm respects the constraints of any argument that is passed to the JVM after the -XX:+AggressiveHeap argument.
Default: | off |
Recommended: | on |
Usage: | -XX:+AggressiveHeap enables automatic tuning of the Java heap |
This setting optimizes the JVM for applications with many short-lived objects. If this parameter is not specified, the JVM usually does a major (full) garbage collection. Full garbage collections can take several seconds and can significantly degrade server performance.
Default: | off |
Recommended: | on |
Usage: | -Xoptgc enables optimized garbage collection. |
The Java heap is divided into a section for old (long lived) objects and a section for young objects. The section for young objects is further subdivided into the section where new objects are allocated, called eden, and the section where new objects that are still in use survive their first few garbage collections before being promoted to old objects, called survivor space. Survivor ratio is the ratio of eden to survivor space in the young object section of the heap. Increasing this setting optimizes the JVM for applications with high object creation and low object preservation. Because WebSphere Application Server instances generate more medium and long lived objects than other application servers, this setting should be lowered from the default.
Default: | 32 |
Recommended: | 16 |
Usage: | -XX:SurvivorRatio=16 |
This setting specifies the number of collections that an object can remain in the new generation before it is promoted to the old generation. Raising the value specified for this setting forces objects to stay in the new generation longer. Lowering the value specified for this setting causes objects to get promoted to the old generation sooner.
Default: | 31 |
Recommended: | 32 |
Usage: | -XX:MaxTenuringThreshold=32 |
This command disables the lazy swap functionality and allows the operating system to use larger memory pages, thereby optimizing access to the memory that makes up the Java heap. By default, the Java heap is allocated lazy swap space. Lazy swap functionality saves swap space because pages of memory are allocated as needed. However, the lazy swap functionality forces the use of 4KB pages. In large heap systems, this allocation of memory can spread the heap across hundreds of thousands of pages.
Default: | off |
Recommended: | on |
Usage: | -XX:+ForceMmapReserved disables the lazy swap functionality. |
This command enables parallel garbage collection for the new generation. Issuing this command on a multi-processor system, can decrease the amount of time that it takes the JVM to complete a partial garbage collection cycle.
Default: | off |
Recommended: | on |
Usage: | -XX:+UseParallelGC enables parallel garbage collection for the new generation. |
This command enables parallel garbage collection for the old generation. Issuing this command on a multi-processor system can decrease the amount of time that it takes for the JVM to complete a full garbage collection cycle.
Default: | off |
Recommended: | on |
Usage: | -XX:+UseParallelOldGC enables parallel garbage collection for the old generation |
This setting controls how much space the young generation is allowed to consume on the heap. Properly tuning this parameter can reduce the overhead of garbage collection, improving server response time and throughput. The default setting for this is typically too low, resulting in a high number of minor garbage collections.
Default: | No default |
Recommended: | Approximately 3/4 of the total heap size |
Usage: | -Xmn768m sets the size to 768 megabytes. |
Setting the Java virtual machine instruction and data page sizes to 64MB can improve performance.
Default: | 4MB |
Recommended: | 64MB |
Usage: | Use the following command. The command output provides the current
operating system characteristics of the process executable:chatr +pi64M +pd64M /opt/WebSphere/ AppServer/java/bin/PA_RISC2.0/ native_threads/java |
By default the JVM unloads a class from memory when there are no live instances of that class left, but this can degrade performance. Turning off class garbage collection eliminates the overhead of loading and unloading the same class multiple times.
If a class is no longer needed, the space that it occupies on the heap is normally used for the creation of new objects. However, if you have an application that handles requests by creating a new instance of a class and if requests for that application come in at random times, it is possible that when the previous requester is finished, the normal class garbage collection will clean up this class by freeing the heap space it occupied, only to have to re-instantiate the class when the next request comes along. In this situation you might want to use this option to disable the garbage collection of classes.
Default: | class garbage collection is enabled. |
Recommended: | class garbage collection is disabled. |
Usage: | Xnoclassgc disables class garbage collection. |
For additional information on tuning the HP virtual machine, see Java technology software HP-UX 11i.
-XX:SchedulerPriorityRange=SCHED_NOAGE -XX:-ExtraPollBeforeRead -XX:+UseSpinning -Djava.nio.channels.spi.SelectorProvider=sun.nio.ch.DevPollSelectorProvider
For additional information on tuning the HP virtual machine,
see Java
technology software HP-UX 11i.
The Java Virtual Machine that WebSphere Application Server uses on the Solaris platform runs in two modes: client or server. Each mode has its advantages.
If you want to maximize performance on application servers that are rarely restarted you should run the HotSpot JVM in server mode. When the JVM is in server mode, it takes several times longer for an application server to get to a state where it can service a large number of requests. However, after it gets to that state, server mode can significantly out perform a comparable JVM running in client mode.
The HotSpot JVM running in server mode uses a high optimization compiler that optimizes and re-optimizes the Java code during the initial warm up stage. All of this optimization work takes awhile, but once the JVM is warmed up, application servers run significantly faster than they do in client mode on the same hardware.
The Solaris implementation of Java 5.0 examines your hardware and tries to select the correct JVM mode for your environment. If the JVM determines that it is running on a server level machine, the JVM automatically enables server mode. In Java 1.4.2 and earlier, the default mode is client mode and must use the -server flag on the JVM command line to enable server mode.
Because the JVM automatically enables server mode if your machine has at least 2 CPUs and 2 GB of memory, your JVMs probably default to server mode. However, you can use the -client and -server flags in the generic JVM arguments to force the virtual machine into either mode if the mode the JVM selects for you does not fit your environment.
The share classes option of the IBM Java 2 Runtime Environment (J2RE) Version 1.5.0 lets you share classes in a cache. Sharing classes in a cache can improve startup time and reduce memory footprint. Processes, such as application servers, node agents, and deployment managers, can use the share classes option.
If you use this option, you should clear the cache when the process is not in use. To clear the cache, either call the app_server_root/bin/clearClassCache.bat/sh utility or stop the process and then restart the process.
If you need to disable the share classes option for a process, specify the generic JVM argument -Xshareclasses:none for that process:
Default: | The Share classes in a cache option is enabled. |
Recommended: | Leave the share classes in a cache option enabled. |
Usage: | -Xshareclasses:none disables the share classes in a cache option. |
-client -XX:MaxPermSize=256m -XX:-UseLargePages -XX:+UseSerialGC
Setting these parameters might impact some throughput
and might result in slightly slower server startup times. If you are running
very large applications, you can specify a higher value for the MaxPermSize
setting.
-XX:-UseParallelGC –XX:-UseAdaptiveSizePolicySetting these parameters might result in slightly slower server startup times.
If you use DB2, consider disabling SafepointPolling technology in the HP virtual machine for Java for HP-UX. Developed to ensure safepoints for Java threads, SafepointPolling technology generates a signal that can interfere with the signal between WebSphere Application Server and a DB2 database. When this interference occurs, database deadlocks often result. Prevent the interference by starting the JVM with the -XX:-SafepointPolling option, which disables SafepointPolling during runtime.
In this information ...Related tasks
Tuning the application serving environment Related reference
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