Selected Examples

Scanning a Queue

In the preceding example, transactions balked from a queue at a time scheduled, by a trigger, before the transaction entered the queue. Similar behavior can be modeled by periodically scanning all the transactions in a queue and balking those transactions that meet some criteria that may be based on the state of the system.

Figure 9.4: Scanning a Queue

Figure 9.4 shows a simple model where the scanning process controls the periodic searching of the queue in the main process. The sampler in the section labeled "Scanning Process" has deterministic, inter-arrival time distribution so that at fixed times a transaction gets a formula and goes to the Trigger that starts the scan of the queue. The formula has where the transaction attribute is random. Since the trigger is set to the queue in the main process and the filter trigger message, when the transaction arrives at the Trigger, the queue is scanned and each transaction whose value of the random attribute is less than .8 is balked.

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