Hi Mark,
Yes, some vendors do preserve timer data across deployments. We just never have in SUN's timer implementation. The topic has come up on the EJB 3.1 Expert Group but it's unlikely to be standardized. To some extent, the proposed EJB 3.1 timer facilities mitigate the issue since there will be support for automatic creation of timers based on a cron-like schedule.
Performance-wise, the database overhead of persistent timers is likely to dominate that kind of scale out. I haven't done any specific tuning exercises for very large timer apps but I'd be interested in hearing any feedback you have on your results. We're also planning to introduce a non-persistent timer option in EJB 3.1. It has a few benefits but one is reduced overhead. That might be a better fit for fine-grained timers and/or very large numbers of timers.
--ken
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