Application Design Factors Affecting Performance

Application design decisions can have a significant effect on overall messaging performance.

The most important factors affecting performance are those that affect the reliability of message delivery. Among these are the following:

• Delivery Mode (Persistent/Nonpersistent Messages)

• Use of Transactions

• Acknowledgment Mode

• Durable and Nondurable Subscriptions

Other application design factors affecting performance are the following:

• Use of Selectors (Message Filtering)

• Message Size

• Message Body Type

The sections that follow describe the effect of each of these factors on messaging performance. As a general rule, there is a tradeoff between performance and reliability: factors that increase reliability tend to decrease performance.

Table 13–1 shows how the various application design factors generally affect messaging performance. The table shows two scenarios—one high-reliability, low-performance, and one high-performance, low-reliability—and the choices of application design factors that characterize each. Between these extremes, there are many choices and tradeoffs that affect both reliability and performance.

Table 13–1 Comparison of High-Reliability and High-Performance Scenarios

Application Design Factor	High-Reliability, Low-Performance Scenario	High-Performance, Low-Reliability Scenario
Delivery mode	Persistent messages	Nonpersistent messages
Use of transactions	Transacted sessions	No transactions
Acknowledgment mode	AUTO_ACKNOWLEDGE or CLIENT_ACKNOWLEDGE	DUPS_OK_ACKNOWLEDGE
Durable/nondurable subscriptions	Durable subscriptions	Nondurable subscriptions
Use of selectors	Message filtering	No message filtering
Message size	Large number of small messages	Small number of large messages
Message body type	Complex body types	Simple body types

Delivery Mode (Persistent/Nonpersistent Messages)

Persistent messages guarantee message delivery in case of broker failure. The broker stores the message in a persistent store until all intended consumers acknowledge they have consumed the message.

Broker processing of persistent messages is slower than for nonpersistent messages for the following reasons:

• A broker must reliably store a persistent message so that it will not be lost should the broker fail.

• The broker must confirm receipt of each persistent message it receives. Delivery to the broker is guaranteed once the method producing the message returns without an exception.

• Depending on the client acknowledgment mode, the broker might need to confirm a consuming client’s acknowledgment of a persistent message.

For both queues and topics with durable subscribers, performance was approximately 40% faster for nonpersistent messages. We obtained these results using 10k-sized messages and AUTO_ACKNOWLEDGE mode.

Use of Transactions

A transaction is a guarantee that all messages produced in a transacted session and all messages consumed in a transacted session will be either processed or not processed (rolled back) as a unit.

Message Queue supports both local and distributed transactions.

A message produced or acknowledged in a transacted session is slower than in a nontransacted session for the following reasons:

• Additional information must be stored with each produced message.

• In some situations, messages in a transaction are stored when normally they would not be (for example, a persistent message delivered to a topic destination with no subscriptions would normally be deleted, however, at the time the transaction is begun, information about subscriptions is not available).

• Information on the consumption and acknowledgment of messages within a transaction must be stored and processed when the transaction is committed.

---

Note –

To improve performance, Message Queue message brokers are configured by default to use a memory-mapped file to store transaction data. On file systems that do not support memory-mapped files, you can disable this behavior by setting the broker property imq.persist.file.transaction.memorymappedfile.enabled to false.

---

Acknowledgment Mode

One mechanism for ensuring the reliability of JMS message delivery is for a client to acknowledge consumption of messages delivered to it by the Message Queue broker.

If a session is closed without the client acknowledging the message or if the broker fails before the acknowledgment is processed, the broker redelivers that message, setting a JMSRedelivered flag.

For a nontransacted session, the client can choose one of three acknowledgment modes, each of which has its own performance characteristics:

• AUTO_ACKNOWLEDGE. The system automatically acknowledges a message once the consumer has processed it. This mode guarantees at most one redelivered message after a provider failure.

• CLIENT_ACKNOWLEDGE. The application controls the point at which messages are acknowledged. All messages processed in that session since the previous acknowledgment are acknowledged. If the broker fails while processing a set of acknowledgments, one or more messages in that group might be redelivered.

• DUPS_OK_ACKNOWLEDGE. This mode instructs the system to acknowledge messages in a lazy manner. Multiple messages can be redelivered after a provider failure.

(Using CLIENT_ACKNOWLEDGE mode is similar to using transactions, except there is no guarantee that all acknowledgments will be processed together if a provider fails during processing.)

Acknowledgment mode affects performance for the following reasons:

• Extra control messages between broker and client are required in AUTO_ACKNOWLEDGE and CLIENT_ACKNOWLEDGE modes. The additional control messages add additional processing overhead and can interfere with JMS payload messages, causing processing delays.

• In AUTO_ACKNOWLEDGE and CLIENT_ACKNOWLEDGE modes, the client must wait until the broker confirms that it has processed the client’s acknowledgment before the client can consume additional messages. (This broker confirmation guarantees that the broker will not inadvertently redeliver these messages.)

• The Message Queue persistent store must be updated with the acknowledgment information for all persistent messages received by consumers, thereby decreasing performance.

Durable and Nondurable Subscriptions

Subscribers to a topic destination fall into two categories, those with durable and nondurable subscriptions.

Durable subscriptions provide increased reliability but slower throughput, for the following reasons:

• The Message Queue message service must persistently store the list of messages assigned to each durable subscription so that should a broker fail, the list is available after recovery.

• Persistent messages for durable subscriptions are stored persistently, so that should a broker fail, the messages can still be delivered after recovery, when the corresponding consumer becomes active. By contrast, persistent messages for nondurable subscriptions are not stored persistently (should a broker fail, the corresponding consumer connection is lost and the message would never be delivered).

We compared performance for durable and nondurable subscribers in two cases: persistent and nonpersistent 10k-sized messages. Both cases use AUTO_ACKNOWLEDGE acknowledgment mode. We found an effect on performance only in the case of persistent messages which slowed durables by about 30%

Use of Selectors (Message Filtering)

Application developers often want to target sets of messages to particular consumers. They can do so either by targeting each set of messages to a unique physical destination or by using a single physical destination and registering one or more selectors for each consumer.

A selector is a string requesting that only messages with property values that match the string are delivered to a particular consumer. For example, the selector NumberOfOrders >1 delivers only the messages with a NumberOfOrders property value of 2 or more.

Creating consumers with selectors lowers performance (as compared to using multiple physical destinations) because additional processing is required to handle each message. When a selector is used, it must be parsed so that it can be matched against future messages. Additionally, the message properties of each message must be retrieved and compared against the selector as each message is routed. However, using selectors provides more flexibility in a messaging application.

Message Size

Message size affects performance because more data must be passed from producing client to broker and from broker to consuming client, and because for persistent messages a larger message must be stored.

However, by batching smaller messages into a single message, the routing and processing of individual messages can be minimized, providing an overall performance gain. In this case, information about the state of individual messages is lost.

In our tests, which compared throughput in kilobytes per second for 1k, 10k, and 100k-sized messages to a queue destination and AUTO_ACKNOWLEDGE acknowledgment mode, we found that nonpersistent messaging was about 50% faster for 1k messages, about 20% faster for 10k messages, and about 5% faster for 100k messages. The size of the message affected performance significantly for both persistent and nonpersistent messages. 100k messages are about 10 times faster than 10k, and 10k are about 5 times faster than 1k.

Message Body Type

JMS supports five message body types, shown below roughly in the order of complexity:

• BytesMessage contains a set of bytes in a format determined by the application.

• TextMessage is a simple Java string.

• StreamMessage contains a stream of Java primitive values.

• MapMessage contains a set of name-value pairs.

• ObjectMessage contains a Java serialized object.

While, in general, the message type is dictated by the needs of an application, the more complicated types (MapMessage and ObjectMessage) carry a performance cost: the expense of serializing and deserializing the data. The performance cost depends on how simple or how complicated the data is.