IBM BPM, V8.0.1, All platforms > Authoring services in Integration Designer > Developing monitor models > Debugging monitor models > Stepping through a running monitor model
Work with event queues
The Event Queues view shows the input queue, retry queue, and error queue. The number of events in each queue is shown on the tab next to the queue name. You can open an event in any of the queues and inspect the content. You cannot change the content of an event in a queue, or the order of the events.
The Event Queues view refreshes each time the debugger finishes processing an event. Sometimes you might want to refresh the view manually, such as if you send more events while stepping through an event in the debugger. You will see the new events in the input queue only when you refresh the view or when you finish processing the current event.
To view the latest content in the event queues, click Refresh 
.
You can find a specific event, or set of events, using either of the following methods:
- Type text into the filter text box. Only events that contain the text are shown.
- Click Classify Events
. The inbound event definition (or definitions) that each event matches is shown beside the event.
Input queue
The input queue shows the sequence of events that are waiting to be processed by the debugger.
For example, imagine you create a script in the Integrated Test Client that contains four events. If you run the script, you will see three events show up on the input queue. (The first event is sent to the debugger immediately, and can be seen in the Variables view.)
Retry queue
The retry queue shows the events that failed because evaluating the correlation expression for an inbound event returned no matching instances and the model-defined event delivery option for no correlation matches specifies "Retry." When an event is added to the retry queue, you see a message on the console. When you click an event on the retry queue, a message at the bottom of the view shows the number of times that the event has been retried, as well as the reason that the event was placed on the retry queue.
Before retrying an event, you might want to set a breakpoint on the correlation step of the inbound event definition that this event has failed before.
You might also want to submit some other events to create a missing instance, or update an existing instance, so that correlation for the retried event will now succeed.
After the other events on the input queue have been processed and you have created a monitoring context to receive the event or changed the state of a target monitoring context instance, you can send the event from the retry queue to the input queue.
To try an event again, select the event in the retry queue and click Retry Event
. The event is added to the top of the input queue.
Error queue
The error queue shows the events that failed because evaluating the correlation expression for an inbound event returned no matching instances, one matching instance, or multiple matching instances and the model-defined event delivery option for that situation specifies "Treat as error." The error queue also shows the events that failed because an unexpected error (such as division by zero) occurred during processing. When you click an event, a message at the bottom of the view shows the step that failed. The step information is followed by the error message.
One class of failures are unexpected correlation outcomes, as specified in the monitor model.
For example, if no matching instances are expected (for example, for a process start event) the monitor model typically specifies that finding one or more instances should be treated as an error. Or if one matching instance is expected (for example, for a process finished event) the monitor model typically specifies that finding no matching instances, or more than one, represents an error.
Events that fail during processing for other reasons, such as trying to convert the value "ABC" to an integer, are also sent to the error queue. Errors have many causes, such as division by zero, arithmetic overflow, or an input to a function with empty parameters or parameters in the wrong format.