When you start the correlator, you can specify the -Xclock option to disable the correlator’s internal clock. By default, the correlator uses internally generated clock ticks to assign a timestamp to each incoming event. When you specify the -Xclock option, you must send time events (&TIME) to the correlator. These time events set the correlator’s clock.

Use &TIME events in place of the correlator’s internal clock when you want to reproduce the historic behavior of an application. For example, Apama Studio’s Data Player starts a correlator with a command that specifies the -Xclock option. The Data Player then sends &TIME events that let you play back events from the database.

A situation in which you might want to generate &TIME events is when you want to run experiments at faster than real time but still obtain correct timestamp behavior. In this situation, the correlator uses the externally generated time events instead of real time to invoke timers and wait events.

Disabling the correlator’s internal clock, and sending external time events, affects all temporal operations, such as timers and wait statements.

Regardless of whether the correlator generates internal clock ticks, or receives external time events, the correlator assigns a timestamp to each incoming event. The timestamp indicates the time that the event arrived on the context’s input queue. The value of the timestamp is the same as the last internally-generated clock tick or externally-generated time event. For example, suppose you have the following events and clock ticks:

A and B receive a timestamp of 1. C receives a timestamp of 2.

For additional information about using external time events, see, Apama Concepts in Introduction to Apama (available if you selected Developer during installation).