WebSphere eXtreme Scale Best Practices for Operation and Management

Chapter 4. Capacity planning and tuning 63

Assume four servers can provide enough of the throughput that is required (that is, the

number of servers from “4.1.9, “Determining the number of CPUs” on page 60” is

not

greater than 4), then we can fill out all the data in Table 4-2.

Table 4-2 Sizing requirements for data center 1

4.2 Tuning the JVM

In general, few or no special JVM settings are required for a WebSphere eXtreme Scale

environment. This section will provide additional guidance about JVM tuning options that can

help improve performance.

4.2.1 Selecting a JVM for performance

WebSphere eXtreme Scale supports Java SE Version 1.4.2, and later, and works on 32-bit or

64-bit JVMs. The recommendation is to use the latest available version of Java Platform,

Standard Edition for the best performance.

WebSphere Application Server V7 uses the IBM virtual machine for Java (IBM JVM) based on

Java Platform, Standard Edition 6 (Java SE 6.0) on platforms other than Solaris and HP-UX.

For Solaris and HP-UX, the Sun HotSpot JVM is used.

To streamline support issues, it is also recommended that you use the JVM from the

WebSphere run time on any platform that WebSphere Application Server supports. Using a

JVM from another vendor will require that you go to that vendor for JVM-related issues, plus

you might miss out on key features, such as compressed references.

4.2.2 Tuning for efficient garbage collection

Garbage collection is the process of freeing unused objects so that portions of the JVM heap

can be reused. Garbage collection is triggered automatically when there is a request for

memory, for example when creating an object, and when the request cannot be readily

satisfied from the free memory that is available in the heap (allocation failure). WebSphere

WebSphere eXtreme Scale creates temporary objects that are associated with each

transaction. Because these objects affect garbage collection efficiency, tuning garbage

collection is important.

IBM JVM and Sun HotSpot garbage collection schemes

Although the garbage collection function that is provided by the Sun HotSpot and IBM

garbage collectors is the same, the underlying technology differs.

Value Data center 1

Number of servers (physical machines) 4

Number of CPUs 4 * 2 = 8 cores

Total physical memory 26 GB * 4 servers = 104 GB

Number of WebSphere eXtreme Scale

container JVMs

16

MaxHeapSize per JVM, also known as Xmx 5376 m or 5.376 GB

numberOfPartitions 83