How often is a programmatic created EJB Timer executed in a cluster?
cluster-computing, jakarta-ee, java, timer
Solution
First, make sure you have setup timer-service to external shared XA datasource as described here.
Having digged into your question in past, I remember some explanation by devs in mailing-lists, that Glassfish's implementation is as follows:
Say you have node A, B and C in a cluster. Persistent timers created at node A are "owned" by node A (that is timer-events are delivered to node A). If node A fails, then its timers can be migrated to another live node.
Having that Glassfish doesn't support cluster-wide `@Singletons`, you end up with as many timers as calls to `initResetTimer()`. Moreover, each server restart/redeploy will possibly create a new instance of timer per cluster node, in additions to old uncancelled ones, so don't forget to cancel your programmatically created timers :) To avoid this alltogether use declarative `@Schedule(...)` approach and Glassfish will create the timer once across cluster and, hopefully, automatically migrate them on failure.
Hope this helps.
UPDATE:
A programmatically created timer, persistent or non-persistent, will be fired in the JVM/node it was created, regardless of clustered setup or not. You can sum up roughly: number of independent timer instances is equal to the number of calls to `timer.createXxxTimer()`
Problem
In a clustered JEE6 environment (Glassfish 3.1.2), a `@Singleton` bean is/can be created on every cluster node. If this Singleton Bean registers a programmatic timer on its `@PostConstruct` - how often is the `@Timeout` method executed? -- on only one of that singletons (per tick), or once (per tick) for each Singeton that registered that a timer? Below the code is an example what this question mean to this code. ``` @Singleton public class CachedService { @Resource private TimerService timerService; private static final long CACHE_TIMEOUT_DURATION_MS = 60 * 60 * 1000; @PostConstruct void initResetTimer() { this.timerService.createIntervalTimer(CACHE_TIMEOUT_DURATION_MS, CACHE_TIMEOUT_DURATION_MS, new TimerConfig("current user cache timeout", false)); } @Timeout public void executeResetTimer() { this.clearCache(); } } ``` Example: The application runs on 3 nodes in a cluster. Assume the Singleton is instantiated on every node, so the `initResetTimer` is done 3 times in total (once per node). Then the question is: is the cache cleared (`executeResetTimer` is invoked) on all nodes once per hour or not? (I know that the timer ticks not at the same time on all nodes, because the Singleton is instantiated at different times, but this is not the problem/question.)