问题
I am thinking about porting a Spring Quartz based application to EJB 3.1 to see if EJB has improved. I am having problems understanding how fail-over works with the Schedule Timer Service. In Quartz, there are database tables which clustered Quartz instances use. If one node in your cluster crashes, jobs will still get executed on other nodes.
I have been looking at how the Timer Service persists things and it appears to use the file system of the server the Timer was created on. Is this true? I do not see how this would be possible as it would render the Timer Service unusable since it would not support failover.
So i must be missing something. Can anyone help me out with this?
回答1:
The EJB timer service is simply not as advanced as Quartz (with or without Spring).
EJB timers are persisted to an unknown location. It may happen to be the file-system, but it could also be the Windows registry if you happen to be running on Windows, or it could be an LDAP server or whatever.
There was an issue on the EJB spec JIRA for some time about this, and it was discussed on the spec mailing list, but then it was brutally dropped and closed because no one bothered to reply anyone (perhaps because a lot of people were on vacation at the time). It's one of the lamest reasons to close an issue if you'd ask me, but I guess the spec lead sometimes must resort to such measures.
Anyway, in JBoss AS persisting happens to an embedded relational datasource, that on its turn writes to the filesystem. Via propriatary configuration you can point this datasource to any remote DB. Fail-over would have to come from propriatary JBoss functionality as well. Although EJB forbids lots of things for the sake of potential clustering, there's no explicit clustering support in the spec and thus specifically EJB timers are not cluster aware.
回答2:
Not sure if this was available at the time of the question but you can use the 'cluster-ha-singleton' for this, it allows you to create a singleton timer that is invoked from a single cluster node, in case of failover of the chosen node a new node is elected to run the singleton (and therefore the timers)
http://www.jboss.org/quickstarts/eap/cluster-ha-singleton/
It mentions EAP but I am running on AS 7.2.0 fine, the jars are already included in /modules/org/jboss/
来源：https://stackoverflow.com/questions/12934464/jboss-7-1-1-and-the-ejb-3-1-timer-service