Why and when to pass the JMS message payload by reference

Why and when to pass the JMS message payload by reference

When large object messages or bytes messages are sent, the cost in memory and processor use of serializing, deserializing, and copying the message payload can be significant. If you enable the pass message payload by reference properties on a connection factory or activation specification, you tell the default messaging provider to override the JMS 1.1 spec and potentially reduce or bypass this data copying.
New feature: The pass message payload by reference properties, which can provide performance improvements for JMS messaging, are new in this release

Background

The JMS 1.1 spec states that object messages are passed by value. This means that a JMS provider such as the default messaging provider in WAS has to take a copy of the object in ObjectMessage at the time the object is set into the message payload, in case the client application modifies the object after setting it. In practice this means serializing it, as there is no other entirely safe way to take a copy. The specification also states that when a consumer application gets the data from the message, the JMS provider must create and return a copy of that data.
If you enable the "pass message payload by reference" properties, we might get memory and performance improvements for JMS messaging. CAUTION:

The parts of the JMS spec that are bypassed by these properties are defined to ensure message data integrity.
Any of the JMS applications that use these properties must strictly follow the rules that are described in detail below, or you risk losing data integrity.
You should read and understand this entire topic before enabling these properties.

To pass the message payload by reference, you set the following properties on connection factories and activation specifications:

producerDoesNotModifyPayloadAfterSet (for connection factories) or forwarderDoesNotModifyPayloadAfterSet (for activation specifications)

When this property is enabled, object or bytes messages produced by the connection factory or forwarded through the activation specification are not copied when set into the message and are only serialized when absolutely necessary. Applications sending such messages must not modify the data after it has been set into the message.

consumerDoesNotModifyPayloadAfterGet

When this property is enabled, object messages received through the connection factory or activation spec are only serialized when absolutely necessary. The data obtained from those messages must not be modified by applications.

Potential benefits of passing the message payload by reference
The following table shows the conditions under which we might get performance benefits by enabling the "pass message payload by reference" properties. This table makes the following assumptions:

Your JMS applications conform to the rules described in the next section of this topic.
Your message producer and consumer applications run in the same JVM (server), along with the messaging engine that hosts the destination used by these applications.

If the applications run in different servers, or on the z/OS platform (where WAS runs in multiple JVMs), then object messages are serialized and no performance benefits are gained for these messages. Bytes message benefits might still be gained.
There are many internal runtime conditions that can cause the messages to be serialized, so even if the configuration meets all the conditions described in this topic we might gain little or no performance benefit from enabling the "pass message payload by reference" properties.

Table 1. How configuration and runtime factors determine what data is copied, when it is copied, and the potential performance benefit.

Degree of potential performance benefit Configuration and runtime events When the data is copied

No potential benefit
The "pass message payload by reference" properties are not enabled (default behavior).

Object message data is copied as soon as it is set into the message and when it is retrieved from the message.
Bytes message data is copied as soon as it is set into the message and when it is retrieved from the message.
Some potential benefit The "pass message payload by reference" properties are enabled, and either or both of the following conditions are true:

The send or receive message is transacted.
The consumer is not available when the message is produced.

Object message data is only copied when necessary.
Bytes message data is only copied when necessary.
Maximum potential benefit The "pass message payload by reference" properties are enabled, and both of the following conditions are true:

Neither the send nor the receive message is transacted.
The consumer is waiting for the message when it is produced (for example if the consumer is a message-driven bean).

Object message data might never be copied.
Bytes message data is only copied when necessary.

Rules that the JMS applications must obey

The parts of the JMS spec that are bypassed by the "pass message payload by reference" properties are defined to ensure message data integrity. If the JMS applications obey the rules given in the following table, then we can safely enable the "pass message payload by reference" properties on the connection factories and activation specifications that the applications use.
If you enable the "pass message payload by reference" properties for JMS applications that do not follow these rules, then the applications might receive exceptions or, more importantly, the integrity of the message data might be compromised.
Table 2. Rules that the JMS applications must obey, by application type

Application type Rules

JMS producer application
A JMS producer application that sends object messages must not alter the object after it is set into the payload of the message. A JMS producer application that sends bytes messages:

must write data into the message with a single call to writeBytes(byte[]).
must not alter the byte array after it is written into the message.

JMS consumer application
A JMS consumer application that receives object messages must not alter the payload it gets from the message.
JMS forwarder application
A JMS forwarder application receives a message (through a connection factory, or if it is a message-driven bean through an activation specification), then sends the message object on to another destination.
A JMS forwarder application that replaces the payload of the received message with a new payload:

(for object messages) must not alter the object after it is set into the payload of the message.
(for bytes messages):

must write data into the message with a single call to writeBytes(byte[]).
must not alter the byte array after it is written into the message.

Ensuring that the object messages can be serialized

Under normal JMS messaging conditions (that is, when the "pass message payload by reference" properties are not enabled), the data in an object message is serialized as soon as the object is passed to the messaging system, for example on set or send. If the message payload cannot be serialized, then an exception message is immediately returned to the client application.
When the "pass message payload by reference" properties are enabled, the message payload is accepted from the client application without attempting to serialize it. If the system later discovers that the data cannot be serialized, the system can no longer inform the client application that sent the message - and because the data is not serializable, the system cannot persist or transmit the complete message. The message and its properties are stored, but the user data inside the message (the payload) cannot be stored and is discarded. If there are serialization problems when the system tries to convert an object message into a data graph for a mediation, the message payload is discarded and the mediation receives a message with the data value set to null.
If your data cannot be serialized, then it is lost. Therefore you should first test the configuration without enabling the "pass message payload by reference" properties, to check that all data sent into the system is serializable. When the system discovers that an object message cannot be serialized, it writes the following error message (JMS_IBM_ExceptionMessage) to SystemOut.log, where "{0}" is replaced by the class name of the failing object:

CWSIK0200E: An object of class "{0}" has been set into the message payload but it cannot be serialized.

Explanation: An object message sent with the producerDoesNotModifyPayloadAfterSet flag enabled on its connection factory was sent with a payload that was not serializable by the system. This message data has been lost.

Action: Disable the producerDoesNotModifyPayloadAfterSet on the connection factory. Without the flag enabled, the JMS application that sets the object into the message will receive any serialization exception immediately.

The following exception properties are used to indicate that a data object cannot be serialized and has been discarded. JMS applications can find out what has happened from the JMS_IBM_Exception properties. Mediations can find out what has happened from the JMS_IBM_Exception and SI_Exception properties.

JMS_IBM_ExceptionReason

SIRCConstants.SIRC0200_OBJECT_FAILED_TO_SERIALIZE

JMS_IBM_ExceptionTimestamp

The time at which the object failed to serialize, in System.currentTimeMillis() form.

JMS_IBM_ExceptionMessage

Message CWSIK0200E, as previously described.

SI_ExceptionReason

SIRC0200_OBJECT_FAILED_TO_SERIALIZE

SI_ExceptionTimestamp

The time at which the object failed to serialize, in System.currentTimeMillis() form.

SI_ExceptionInserts

A string array containing one entry. The entry contains the class name of the object.

The most likely explanation as to why the data objects cannot be serialized is that we have written your own writeObject() or writeExternal() methods and have not fully tested every option (for example NullPointer exceptions, or ArrayIndexOutOfBounds exceptions).
Last updated Dec 15, 2010 8:14:22 PM CST

Degree of potential performance benefit	Configuration and runtime events	When the data is copied
No potential benefit	The "pass message payload by reference" properties are not enabled (default behavior).	Object message data is copied as soon as it is set into the message and when it is retrieved from the message. Bytes message data is copied as soon as it is set into the message and when it is retrieved from the message.
Some potential benefit	The "pass message payload by reference" properties are enabled, and either or both of the following conditions are true: The send or receive message is transacted. The consumer is not available when the message is produced.	Object message data is only copied when necessary. Bytes message data is only copied when necessary.
Maximum potential benefit	The "pass message payload by reference" properties are enabled, and both of the following conditions are true: Neither the send nor the receive message is transacted. The consumer is waiting for the message when it is produced (for example if the consumer is a message-driven bean).	Object message data might never be copied. Bytes message data is only copied when necessary.

Application type	Rules
JMS producer application	A JMS producer application that sends object messages must not alter the object after it is set into the payload of the message. A JMS producer application that sends bytes messages: must write data into the message with a single call to writeBytes(byte[]). must not alter the byte array after it is written into the message.
JMS consumer application	A JMS consumer application that receives object messages must not alter the payload it gets from the message.
JMS forwarder application A JMS forwarder application receives a message (through a connection factory, or if it is a message-driven bean through an activation specification), then sends the message object on to another destination.	A JMS forwarder application that replaces the payload of the received message with a new payload: (for object messages) must not alter the object after it is set into the payload of the message. (for bytes messages): must write data into the message with a single call to writeBytes(byte[]). must not alter the byte array after it is written into the message.