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Event Registry & Queue

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In this lesson, you will learn:

  • What an event is in ServiceNow
  • How events are registered, fired, and queued
  • How to read the event log

1 A shout-out that something happened

When someone comments on an incident, ServiceNow doesn’t send the email right away. First, it shouts: “incident.commented just happened!” 📣 That shout is an event. Other parts of the platform listen for it and react.

Key term: Event

A message that says “something happened”, like a comment or an assignment. Events are queued, then processed. Notifications and script actions can react to them.

The life of an event. 1 Register: the event name snwr.incident.vip is added to the event registry. 2 Fire: a business rule calls gs.eventQueue with the event name, the record, and two parameters. 3 Queue: the event waits in the event queue with state ready. 4 Process: the event processor picks it up every few seconds. 5 React: a notification sends an email and a script action runs a script.
Figure 1. Register, fire, queue, process, react.

2 The event registry

Before you fire your own event, you register it. Go to System Policy > Events > Registry (sysevent_register).

Field Example
Event name snwr.incident.vip
Table Incident
Fired by SNWR VIP business rule (just a note for people)
Description A VIP caller logged an incident

3 Firing an event

Server-side scripts fire events with gs.eventQueue():

// event name, record, parm1, parm2
gs.eventQueue('snwr.incident.vip', current,
  current.caller_id.toString(), current.assignment_group.toString());

parm1 and parm2 are two extra values you can pass along, like a user or a group.

4 The queue and the log

  • Fired events go into the event queue (the sysevent table) with state ready.
  • A scheduled job, the event processor, picks them up every few seconds and marks them processed.
  • See them in System Policy > Events > Event Log.

💡 Good to know: Why queue events instead of acting right away? The user’s save stays fast. The emails and scripts run a moment later, in the background.

⚠️ Heads up: The event name in gs.eventQueue() must match the registry exactly. A typo means nothing listens, and nothing happens.

⭐ Remember: Register in the Registry, fire with gs.eventQueue(), check the Event Log.

5 Let’s try it: watch events happen

  1. Open System Policy > Events > Event Log. Sort by Created, newest first.
  2. In another tab, add a comment to any incident.
  3. Refresh the log. Do you see incident.commented? What’s its state?
  4. Open Events > Registry and register snwr.incident.vip on the Incident table. You’ll use it in Lesson 41.2.

6 Quick recap

  • An event says “something happened”
  • Register custom events in the event registry
  • Fire them with gs.eventQueue(name, record, parm1, parm2)
  • Events wait in the queue, then the event processor handles them
  • Check the Event Log to see what fired

7 Check yourself

Think of your answer first. Then tap to check.

1 Which method fires an event from a server script? Show answer

gs.eventQueue().

2 Where do you register a new event? Show answer

System Policy > Events > Registry.

3 What are parm1 and parm2? Show answer

Two optional extra values passed with the event, like a user or group sys_id.

Nice work! You finished this lesson. 🎉

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