I assume you must do this over the internet; that you do not have local 
access to the file, but it will help to know that for sure.

If you can access the file locally, then Windows has a few functions that 
will help.

If you cannot access the file locally and must query over the internet, then 
it is possible to query the last modified date and time of a file. If you do 
that, then you don't need to read all the data just to determine if it has 
changed. I forget how to do it; it is something I wanted to do a couple of 
weeks ago but I can't find any of the samples I have of doing it. I thought 
the data was part of the HTTP headers but I don't find it there. Getting the 
last update time of a file over the internet is a very common thing to do 
and I am sure we could find the answer easily if that will help you. I just 
did not pursue it further when I was looking a couple of weeks ago but I 
know I have samples somewhere in my system.


"Elliot" <elliot_barclay@h...> wrote in message 
news:223B8966-8D9E-46FE-89BD-C408E1741988@m......
>I propose to write a C# program to get the content of a xml file.
> However, that file may be modified after 10 seconds, 10 minutes or 10 
> hours.
> I think the algorithm of getting the content every 10 seconds to check 
> whether it was chaged is too stupid, assuming there are 50,000 users 
> running the program(cause a heavy workload for the web server, worse still 
> it is unable to handle).
> Certainly, less than 10-second delay is acceptable if real-time is 
> impossible.
> Please advise me a better algorithm.
> Any idea would be appreciated.
>