In earlier postings I’ve described how TASM system events can detect such things as AMP worker task shortages, and automatically react to change workload managements settings. These system events tell TASM to look out for and gracefully react to resource shortages without your direct intervention, by doing things like adjusting throttle limits temporarily downwards for the less critical work.
This switchover happens as a result of TASM moving you from one Health Condition to another, and as a result, from one state to another state. But how does this shift to a new actually state happen? And under what conditions you will you be moved back to the previous state?
Timers that control the movement between states
Before you use system events to move you between states, you will need to familiarize yourself with a few timing parameters within TASM, including the following:
- System-wide Event Interval - The time between asynchronous checks for event occurrences. It can be set to 5, 10, 30 or 60 seconds, with 60 seconds being the default
- Event-specific Qualification Time – To ensure the condition is persistent, this is the amount of time the event conditions must be sustained in order to trigger the event
- Heath Condition Minimum Duration – Prevents a constant flip-flop between states, the minimum amount of time that a health condition (which points to the new state) must be maintained even when the conditions that triggered the change are no longer present.
Entering a State
Let’s assume you have defined an AWT Available event that triggers when you have only two AMP worker tasks available on any five of your 400 AMPs, with a Qualification Time of 180 seconds. Assume that you have defined the Health Condition associated with the state to have a Minimum Duration of 10 minutes, representing the time that must pass before the system can move back to the original state.
TASM takes samples of database metrics in real-time, looking to see if any event thresholds have been met. It performs this sampling at the frequency of the event interval.
Once a sampling interval discovers the system is at the minimum AMP worker task level defined in the event, a timer is started. No state change takes place yet. The timer continues on as long as each subsequent sample meets the event’s thresholds. If a new event sample shows that the event thresholds are no longer being met, then the timer will start all over again with the next sample that meets the event’s threshold criteria.
Only when the timer reaches the Qualification Time (180 seconds) will the event be triggered, assuming that all samples along the way have met the event’s threshold. At that point TASM moves to the new state.
Exiting a State
Returning to the original state follows a somewhat similar pattern.
The Minimum Duration DOES NOT determine how long you will remain in the new state, but rather it establishes the minimum time that TASM is required to keep you in the new state before reverting back to the original state.
So when will you exit a state?
Event interval sampling continues at the event interval number of seconds all the while you are in the new state. Even if the event threshold criteria is no longer being met and available AWTs are detected to be above the available threshold, once the move to the new state has taken place, the new state remains in control for the Minimum Duration.
After the Minimum Duration number of seconds has been passed, if event sampling continues to show that the AWT thresholds are being met (you still have at least five AMPs with only two AWTs available), TASM will continue to stay in that new state. Only after the first sample that fails to meet the event thresholds is experienced (once the Minimum Duration number of seconds has passed) will control be moved back to the original state.
The bottom line is that you will not return to the original state until the Minimum Duration time of the state's Health Condition has been passed, but you may not be returned then if the condition that triggered the event persists.