EJB3 + JEE6: What is a persistent Timer?

ejb-3.0 timer java-ee-6
Hank picture Hank · Apr 20, 2010 · Viewed 21.2k times · Source

I'm just about to use the new EJB3 TimerService (as part of Java EE 6), and as usual, I'm impressed by the brevity of JavaDoc :)

Do you know what is the effect of the persistent property of the TimerConfig object?

JavaDoc TimerConfig says: The persistent property determines whether the corresponding timer has a lifetime that spans the JVM in which it was created. It is optional and defaults to true.

Answer

Brett Kail picture Brett Kail · Apr 23, 2010

The persistent property means that the container is required to persist the timer state to a database. This is important if you need to guarantee that the timer will fire even if the server is taken offline (intentionally or crash). When the server comes back online, it is required to execute missed timers. Setting a timer as persistent also has the side-effect of ensuring that the timer only executes in one server JVM (but not necessarily the one that created it), whatever that means for your product. For example, in a clustered server environment, this typically means that even if EJB module is running on 3 JVMs, exactly one JVM will execute the timer.

persistent=true was the only option available prior to EJB 3.1. Some timer operations are not critical enough to warrant this level of reliability, so the option was added to allow non-persistent timers. Setting a timer as non-persistent also has the side-effect of ensuring it runs in the JVM in which it was created. This can be useful for updating an in-memory cache or static HTML.

Related questions

Error invoking timeout for timer - could not obtain lock within 5MINUTES at EJB 3 timerservice

I have an application running on jboss 6.1 that defines a lot of dinamyc timers at the startup (e.g doSomething every minute) based on informations already persisted on the database. The timers are created programmatically based on these informations: TimerConfig …

Read More
How to stop endless EJB 3 timer?

I am new to EJB 3 . I use the following code to start endless EJB 3 timer then deploying it on JBOSS 4.2.3 @Stateless public class SimpleBean implements SimpleBeanRemote,TimerService { @Resource TimerService timerService; private Timer timer ; @Timeout public void timeout(Timer timer) { System.…

Read More
Dynamic parameters for @Schedule method in an EJB 3.x

I'm new to the @Schedule annotations in J2EE6 I want to run a job using EJB 3.x with Glassfish 3.1. The javax.ejb.Schedule seems to be a good choice for us, so we could think of our custom time …

Read More