MACROMEDIA COLDFUSION 4.5-ADMINISTRING COLDFUSION SERVER Technical Information download pdf (Page 106)

101

CONFIGURING AND ADMINISTERING COLDFUSION 9

Using the ColdFusion Server Monitor

Last updated 2/21/2012

JVM memory usage

Because ColdFusion is an enterprise Java application, the Java Virtual Machine (JVM) is the software component that

most influences performance. Different JVMs from different vendors and different versions of the same JVM from the

same vendor have different performance characteristics. You might benefit from changing the JVM that you are using

with ColdFusion.

ColdFusion contains an embedded version of JRun 4 as the application server and the Sun 1.6 version of the JVM. By

contrast, ColdFusion for J2EE running on IBM WebSphere Application Server uses the JVM that WebSphere is

configured to use.

To configure ColdFusion to use a different JVM, edit the cf_root/runtime/lib/jvm.config file with a text editor by

modifying the value of java.home to point to the root directory of the JVM to use. Alternatively, you can switch to a

different JVM in the ColdFusion Administrator on the Java and JVM Settings page.

Because switching the JVM changes the software environment significantly, do so first in a development or testing

environment. Also, fully test your ColdFusion applications before you make the change on a production server.

The JVM performs memory management and can have a significant effect on your performance depending on how

you configure the JVM. The most important settings for the JVM are the initial heap size and maximum heap size. The

initial heap size represents the amount of memory that the JVM uses on startup; the maximum heap size represents

the amount of memory that the JVM can use. You can modify these settings in the ColdFusion Administrator on the

Java and JVM Settings page. The Initial Memory Size setting specifies the initial heap size; the Maximum Memory Size

setting specifies the maximum heap size. The JVM arguments for initial heap size and maximum heap size are -

XmsNm

and

-XmxNm respectively, where N is the size of the heap in megabytes (MB). These JVM arguments are stored in the

jvm.config file, in the value of the java.args setting.

The default maximum heap size is set to 512 MB in ColdFusion. For best performance, set the initial heap size and the

maximum heap size to the same value. Determining the optimal size for the heap to run the applications on your

ColdFusion server results in improved performance. Setting the value too high can result in poorer performance

because of the higher degree of garbage collection and internal memory management required for the larger heap.

Conversely, setting the heap size too small can result in a java.lang.OutOfMemoryError error if your application tries

to use more memory than is available to it.

The best way to find the optimal heap size is to run your application under simulated peak load with a large heap and

monitor how much memory your application actually uses. If you find that your application uses only 180 MB of

memory, for example, you might see performance benefit from reducing your heap size to 256 MB.

The java.lang.OutOfMemoryError error can occur in other, more complicated, conditions. One common cause of the

error is when objects fill up the heap's permanent generation, which defaults to 64 MB. You can increase the value, for

example, to 128 MB, by adding the following JVM argument to the Java and JVM Settings page of the ColdFusion

Administrator:

-XX:MaxPermSize=128m.

Physical hardware memory is an important consideration when determining the optimal heap size. Setting the

maximum heap size to a value that exceeds the amount of free physical memory causes severe performance

degradation. For example, if you have only 512 MB of physical memory, do not set the maximum heap size to 512 MB.

Because the operating system and other running applications use memory, much less than 512 MB of memory is

available for the JVM process. it is important to have hardware that meets the requirements of your software

application. For best results, run on server hardware with 1 GB or more of physical memory.

The Server Monitor Summary page monitors the JVM’s memory usage. Use this information when determining the

optimal heap size.

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