当应用程序有两个实例时，如何避免同时执行石英作业

Question

I've got a Spring Web application that's running on two different instances. The two instances aren't aware of each other, they run on distinct servers.

That application has a scheduled Quartz job but my problem is that the job shouldn't execute simultaneously on the instances, as its a mail sending job, it could cause duplicate emails being sent.

I'm using RAMJobStore and JDBCJobStore is not an option for me due to the large number of tables it requires.(I cant afford to create many tables due to internal restriction)

The solutions I thought about: -creating a single control table, that has to be checked everytime a job starts (with repeatable read isolation level to avoid concurrency issues) The problem is that if the server is killed, the table might be left in a invalid state.

-using properties to define a single server to be the job running server. Problem is that if that server goes down, jobs will stop running

Has anyone ever experienced this problem and do you have any thoughts to share?

Answer 1

Start with the second solution (deactivate qartz on all nodes except one). It is very simple to do and it is safe. Count how frequently your server goes down. If it is inacceptable then try the first solution. The problem with the first solution is that you need a good skill in mutithreaded programming to implement it without bugs. It is not so simple if multithreading is not your everyday task. And a cost of some bug in your implementation may be bigger than actual profit.