Write Application Progress to WebService

Question

I have a daily launched multi-threaded loading service. I would like to keep tack of the percentage progress of the loader. I was thinking that it would be good to have an update column on a database table that writes the %Progress. However, I have learned that this may not be a good idea as there will there be a large overhead(5k updates per minute).

I asked this question to stackoverflow http://stackoverflow.com/questions/3275686/store-application-progress-to-database and the respondents informed me that the progress indication is best exposed as a webservice.

Can someone please explain to me how I could implement this? What will the webservice output - xml data such as 'N%' or otherwise? How would a client appication determine the progress - I assume the webservice should expose some sort of notification event that a client application would implement and listen to updates?

Thanks, j.