JBoss Performance Tuning part 1

This is a two part tutorial which discusses about Performance tuning on JBoss AS 4 and 5 and contains some indications about tuning the OS where the application server is running. If you are using a more recent version of the application server, we suggest taking a look at the following articles also:

JBoss Performance Tuning Part 1


JBoss tuning tip 1: Tune the garbage collector

One strength of the J2SE platform is that it shields the developer from the complexity of memory allocation. However, once garbage collection is the principal bottleneck, it is worth understanding some aspects of this hidden implementation

An object is considered garbage when it can no longer be reached from any pointer in the running program. The most straightforward garbage collection algorithms simply iterate over every reachable object. Any objects left over are then considered garbage. The time this approach takes is proportional to the number of live objects,
The complete address space reserved for object memory can be divided into the young and tenured generations.


jboss performance tuning tutorial

The young generation consists of eden and two survivor spaces. Most objects are initially allocated in eden. One survivor space is empty at any time, and serves as the destination of any live objects in eden and the other survivor space during the next copying collection. Objects are copied between survivor spaces in this way until they are old enough to be tenured (copied to the tenured generation).

A third generation closely related to the tenured generation is the permanent generation which holds data needed by the virtual machine to describe objects that do not have an equivalence at the Java language level. For example objects describing classes and methods are stored in the permanent generation
Use the the command line option -verbose:gc causes information about the heap and garbage collection to be printed at each collection. For example, here is output from a large server application:

jboss performance tuning

It's demonstrated that an application that spends 10% of its time in garbage collection can lose 75% of its throughput when scaled out to 32 processors
(http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html)

JBoss tuning tip 2: Set -Xms and -Xmx to the same value

By default, the virtual machine grows or shrinks the heap at each collection to try to keep the proportion of free space to live objects at each collection within a specific range. Setting -Xms and -Xmx to the same value. This increase predictability by removing the most important sizing decision from the virtual machine.

JBoss tuning tip 3: Use server VM

The server JVM is better suited to longer running applications. To enable it simply set the -server option on the command line.

JBoss tuning tip 4:  Turn off distributed gc

The RMI system provides a reference counting distributed garbage collection algorithm. This system works by having the server keep track of which clients have requested access to remote objects running on the server. When a reference is made, the server marks the object as "dirty" and when a client drops the reference, it is marked as being "clean.". However this system is quite expensive and by default runs every minute.

Set it to run every 30 minute at least

-Dsun.rmi.dgc.client.gcInterval=1800000
-Dsun.rmi.dgc.server.gcInterval=1800000

JBoss tuning tip 6:  Turn on parallel gc

If you have multiple proessors you can do your garbage collection with multiple threads. By default the parallel collector runs a collection thread per processor, that is if you have an 8 processor box then you'll garbage collect your data with 8 threads. In order to turn on the parallel collector use the flag -XX:+UseParallelGC. You can also specify how many threads you want to dedicate to garbage collection using the flag -XX:ParallelGCThreads=8.

JBoss tuning tip 7: Don't use Huge heaps, use a cluster

More JVMs/smaller heaps can outperform fewer JVMs/Larger Heaps. So instead of huge heaps, use additional server nodes. Set up a JBoss cluster and balance work between nodes.

JBoss tuning tip 8: Don't choose an heap larger then 70% of your OS memory

Choose a maximum heap size not more then 70% of the memory to avoid excessive page faults and thrashing.  

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