The real purpose of "refresh-interval" in EJB timer service (wildfly 10.1.0.Final)

[wwang2016]

Hi,

I am testing setting EJB timer/scheduler in a wildfly cluster with two instances (#1 and #2)

I had a basic configuration that is actually working. Either of the instances will invoke the scheduler at specified time, no repeating invocation was happening. This is good.

However, I also understand there is a parameter called "refresh-interval" which I did not set it up. Based on the model reference (Wildfly Model Reference ) ,

• refresh-interval Interval between refreshing the current timer set against the underlying database. A low value means timers get picked up more quickly, but increase load on the database.

The default value is -1

It looks like a parameter that can affect performance.

I am not very clear as to what this parameter does. When I decompiled a java class called DatabaseTimerPersistence.java, and found the method start(StartContext context), it has the following code:

        if(refreshInterval > 0)

        {

            refreshTask = new RefreshTask();

            ((Timer)timerInjectedValue.getValue()).schedule(refreshTask, refreshInterval, refreshInterval);

        }

It seems to me that the default value will not invoke the above code.

However, I can see clearly the scheduler in cluster environment worked fine (schedule to invoke the job every 30 seconds)

Can anyone share with me what it does?

Thanks

Wayne

[wdfink]

If timers use the database as persistence, it might happen that node1 will add a timer (by deployment if scheduled, or programatic for any SLSB).

In this case the node2 is not aware of it.

So in case of node1 crashes the timer is not executed at node2 until the node refresh the timer from the persistence.

The refresh-interval can be used for this, you need to decide based on your potential risk.

Removed timers are not executed as they are updated on timeout before started, you'll see a message that the timer is cancled.

Make sense? Any further question?

[wwang2016]

Hi Wolf-Dieter,

In the scenario you discussed, it is important to set this value to some number, instead of leave it as default (-1). The default value will make this parameter useless and it can be an issue in cluster environment.

In your experience, what would be a reasonable value?

Thanks,

Wayne

[wdfink]

That depends on the requirements.

If you have timers running every let's say minute and it is important that you don't miss it you need to set something around a minute.

If you have timers which need only to be exact for the day you might choose a refresh of 0.5 to 1 day

[wwang2016]

Thanks a lot!

Wayne