How to implement job groups/batches

[Shane]

I'd like to be able to tie a number of jobs together as a group and queue up another job whenever they are all done (by the same worker, multiple workers, doesn't matter). The way I have thought to do this is to, after each job is completed, make a worker select a limit 1 from the jobs table where group_id matches the group_id of a job just completed. I'm not sure what this will do for performance, though. Any thought on whether or not this is a good idea, or what a better way would be? Has anyone already done this?