I am creating a system where users can setup mailings to go out at specific times. Before I being I wanted to get some advice. First, is there already a .Net component that will handle scheduling jobs (either running another application or calling a URL) that will do what I am suggesting (Open Source would be cool)? If there isn’t, is it better to schedule a job in SQL and run some sort of script, create a .Net service that will look at an xml file or db for schedules, or have an application create scheduled tasks? There could be a ton of tasks, so I am thinking creating scheduled tasks or SQL jobs might not be a good idea. Here may be a typical scenario; a user wants to send a newsletter to their clients. The user creates the newsletter on a Saturday, but doesn’t want it to go out until Monday. The user wants that same e-mail to go out every Monday for a month. Thanks for looking!
Check out Quartz.NET
Quartz.NET is a full-featured, open source job scheduling system that can be used from smallest apps to large scale enterprise systems.
If you want to use the readily available services in Windows itself, check out this article A New Task Scheduler Task Library on CodeProject on how to create scheuled tasks in Windows from your C# application.
You probably have more flexibility and power if you use C# and scheduled tasks in Windows, rather than limiting yourself to what can be done in SQL Server. SQL Server Agent Jobs are great - for database specific stuff, mostly - maintenance plans and so forth.
You can build your own windows service that schedules and executes jobs. Be sure to make good abstractions. In a similar project, I have used an abstraction where scheduling items are abstracted as Jobs composed of tasks. For example, sending newsletter may be a job whereas sending newsletter to each subscriber can be considered as a task. Then you need to run the job and tasks in defined threading models preferably using Threadpool threads or Task Parallel Library. Be sure to use asynchronous API for IO whenever possible. Also separate your scheduling logic from the abstractions. so that the scheduling logic can execute arbitrary types of jobs and its inclusive tasks.