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 specification and potentially reduce or bypass this data copying.
Background
The JMS 1.1 specification states that object messages are passed by value. This means that a JMS
provider such as the default messaging provider in WebSphere® Application Server 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, you might get memory and performance improvements for JMS messaging.
- The parts of the JMS specification that are bypassed by these properties are defined to ensure message data integrity.
- Any of your JMS applications that use these properties must strictly follow the rules that are described in detail later in this section, or you risk losing data integrity.
- You should read and understand this entire topic before enabling these properties.
- 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 specification 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
- 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 your applications run in different servers, or on the z/OS® platform (where WebSphere Application Server 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 your messages to be serialized, so even if your configuration meets all the conditions described in this topic you might gain little or no performance benefit from enabling the pass message payload by reference properties.
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:
|
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:
|
Object message data might never be copied. Bytes message data is only copied when necessary. |
Rules that your JMS applications must obey
The parts of the JMS specification that are bypassed by the pass message payload by reference properties are defined to ensure message data integrity. If your JMS applications obey the rules given in the following table, then you 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.
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:
|
JMS consumer application |
A JMS consumer application that receives object messages must not alter the payload it gets from the message. |
JMS forwarder application Note: 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:
|
Ensuring that your 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 your configuration without enabling the pass message payload by reference properties, to check that all data sent into the system is serializable.
SystemOut.log
file, 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.
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.
writeObject()
or writeExternal()
methods and have
not fully tested every option (for example NullPointer
exceptions, or
ArrayIndexOutOfBounds
exceptions).