WebSphere eXtreme Scale Best Practices for Operation and Management

128 WebSphere eXtreme Scale Best Practices for Operation and Management

Dealing with efficient serialization will not greatly complicate the programming model of an

application or corporate application standard. The modest skill that is needed to write the two

Externalizable methods can be learned quickly and only requires simple Java skill to begin.

The efficient serialization logic can be put in the Externalizable methods for use with other

serialization-using functions, such as HTTPSession replication. This efficient serialization

logic can be put in the same Externalizable methods in the objects being stored in

WebSphere eXtreme Scale, in a separate class implementing the WebSphere eXtreme Scale

ObjectTransformer interface and attached to the WebSphere eXtreme Scale map, or split

between them. The efficiency that you can gain is the same for any of these three (except as

mentioned in the next paragraph).

The following article provides a good description of how serialization in Java works:

򐂰 “The Java serialization algorithm revealed”

http://www.javaworld.com/community/node/2915

This article does not mention Externalizable specifically, but it does give you an idea of the

overhead that you can avoid by using both Externalizable and the WebSphere eXtreme Scale

ObjectTransformer interface.

The following article describes Serialization more broadly, including Externalizable (note the

paragraph about “Performance Considerations” near the end, which recommends that you

“write your own protocol” to achieve the best performance, which is what we have explained

how to do here):

򐂰 “Discover the secrets of the Java Serialization API”

http://java.sun.com/developer/technicalArticles/Programming/serialization/

It is not always necessary to have efficient serialization, although usually it is. Efficient

serialization makes the operation of WebSphere eXtreme Scale faster for that object. Gets

are faster, because there is less data to flow over the wire from the WebSphere eXtreme

Scale container to the client application. Puts are faster for the reverse flow from the client to

the container and the replica container. In both cases, far less CPU is used when the logic is

efficient. However, if the logic using the object is not performance-sensitive (if it is used

infrequently and if getting the object is one small part of an already long operation), you might

not have to bother. Performance testing will let you know.

Existing packages for improved serialization with less writing code

There are packages on the Internet that can help you improve serialization. WSSUtils also

includes serialization support. Neither of these packages is as efficient as writing your own

code, but they require substantially less coding, because they both use modern introspection.

You merely have to assert in one line that you want a given class to have serialization done.

We have not tested either of these packages as of the time of publishing this book.

6.4.2 Implementing the Externalizable interface

When you implement the Externalizable interface, you are then required by the interface

contract to provide implementations of the readExternal(java.io.ObjectInput in) and the

writeExternal(java.io.ObjectOutput out) methods. You get complete control over the

serialization process. See Example 6-8.

Example 6-8 Externalizable example

public class User implements Externalizable implements Cloneable {

private static final long serialVersionUID = 1L;