How SharePoint Timer Service 'OWSTimer' Works?

In our application, we need to build something similar to SharePoint timer service. This service needs to be installed on all web servers in a farm. A job can be scheduled to be run immidiately, daily, weekly or monthly on any or all web servers of the farm. Jobs configuration and schedule is stor开发者_StackOverflow社区ed in database (MS SQL 2008).

How SharePoint timer service executes these jobs exactly at the scheduled times?

• Does it get notified by SQL Server? (Notification services not available in SQl Express)
• Does it poll SQL Server after specific intervals to find if any job needs execution? (Does not guarantee precision.)
• Or what?

I would recommend that you use an existing framework

http://quartznet.sourceforge.net/

https://stackoverflow.com/questions/tagged/quartz.net