You have different options to handle it but it depends on your requirement.
One of those , Tadit has already suggested which uses Global.asax application event for the periodical DB updates. But can go through the link about the risk involved
http://haacked.com/archive/2011/10/16/the-dangers-of-implementing-recurring-background-tasks-in-asp-net.aspx/[
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Even implementing IHttpModule interface will can be helpful.
Or other option is to use timer in Masterpage .
May be one more option is to have a webservice and add a windows service to schedule the updations periodically.
http://msdn.microsoft.com/en-us/magazine/cc163821.aspx[
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Hope this helps you...