Overview of GMD

Under normal operation in SmartSockets, all messages sent through connections are delivered successfully and processed in a timely manner. If a network failure occurs, however, data can be lost. For some applications, such as bank transactions or Internet commerce, missed messages or duplicate messages are unacceptable. With GMD, an RTclient can stay informed as to whether a message was delivered to some or all subscribers. GMD fully recovers from failures and ensures that messages are transmitted as required.

memory-based GMD

file-based GMD

Memory-based GMD works well for transient network problems, but it does not protect an RTclient from system crashes. Because it stores the messages only in memory, a system crash before the message is delivered can cause the message to be lost.

File-based GMD writes the messages to a file, which can be accessed for re-delivery if there is a system crash. This means file-based GMD is much more reliable, but slower than memory-based GMD. For any software product, performance is slower when data is written to disk frequently and that performance depends on the speed of your local file system. However, writing crucial information, such as a message, to disk is still the best way to ensure system reliability.

When deciding whether to use GMD, you need to decide what is most important for your system, balancing performance and reliability, and determining your tolerance for missed or duplicate messages in the event of network and system crashes.

GMD Features

persistence of messages, stored safely in disk files in case a program crashes and is restarted

transparent operation with automatic file management and acknowledgment of delivery

notification when GMD fails, to allow flexible recovery procedures that you design

easy to use

Simply set the delivery mode property of a message using the setDeliveryMode method on the TipcMsg class or the TipcMt class, and set the delivery timeout property of a message with setDeliveryTimeout on the TipcMsg class or the TipcMt class.

easy to configure

Use the default settings, or set the few GMD-related options in your option database.

industry benchmark performance that is limited only by the speed of your local file system and the network

How GMD Works

After you initially configure GMD for your system, certain steps occur automatically, without any intervention. Figure 10 shows the order of events:

Message is sent to RTserver.

Message is sent to Receiver.

After processing message, highest sequence number is updated.

Acknowledgment message is sent to RTserver.

Acknowledgment message is sent to Sender.

Message is deleted from GMD area.