How often does the data in the table change? Even if the clients poll once
a minute would they be getting new results each time?

I ask because it may be worth your while to make a "proxy web service".
Once that your clients can call, which would in turn call the real web
service but cache the data for 1 or so minutes. Only when the cache expires
would the proxy web service actually call the real web service and update
the cache. That way the real web service only gets called 1 time every
minute and there's only a database hit 1 time every minute. Your proxy web
service would get hit a lot but 99% of the time it would be dishing out
cached data, making it able to serve more hits. The bottle neck now becomes
your proxy web service, but if you found the load on that web service was
too high, you could put it on more than one server, splitting the load up.


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I would use the async APIs available (either Socket or HttpWebRequest
class, using the Begin/EndXXX methods). These will use i/o completion
ports, which implicitly use a thread pool but which don't require you to
implement threading explicitly. Use of i/o completion ports is also
required for the most scalable i/o code.

Now, use of i/o completion ports (and in .NET, implicitly via the async
API) doesn't in and of itself guarantee scalability. There can be other
problems in the code that reduce performance. And conversely, depending
on the code it may not be necessary to use i/o completion ports in order
to achieve high bandwidth.

In particular, if you've got some well-defined small amount of data to
just send repeatedly on a variety of connections, it's possible you
could handle that just fine in a single thread. Network i/o is going to
be a LOT slower than your CPU bandwidth, and once you've completely
saturated your network connection, it doesn't matter how efficient the
rest of the code is, it can't go any faster.

That said:

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It seems to me that your concerns are valid, at least to some extent.

As far as the network traffic goes, that really just depends on your
network. If you're doing this testing over a LAN, there's probably no
problem. For that matter, if you're doing it over an Internet
connection and the requests are very small, there's probably no problem.

But sure, if you're sending 100K of something out in a minute, that
something needs to be small enough to fit in your network bandwidth.
Hopefully that's the case here, but you're not specific about the size
of the requests, so it's hard to answer with a specific yes or no. As a
rough estimate, I calculate that on a relatively slow connection
(128Kbps, early-adopter cable modem upload speed), you can only do 100K
8-byte items in 60 seconds. Even a 1Mbps upload speed only gets you to
64-byte requests.

So it all depends, on your network speed and the size of the requests
(and those calculations are just rough estimates...actual network
performance and overhead does vary).

As far as the web service itself, I would be concerned as to whether you
are actually measuring what you think you're measuring. Depending on
the implementation, it could handle 100K requests from the same client
better than it can handle 100K requests from thousands of clients. So
at the very least, you may want to make sure that your client is
configured so that it _looks_ like multiple clients, from the web
service's point of view.

This sort of testing _is_ done, of course. So it's certainly possible.
You just need to be aware of the requirements for achieving the server
load you're looking for.

Thanks for all the replies. The app will be a windows service that simply
saves the data in a local SQL server. The data changes very frequently - its
call log data from a VOIP phone system and the offices that use them are on
the phone all day! i think the problem is how the web service has been
designed - i can only bring back the last 50 entries on a per user (phone)
basis so if i didn't poll frequently enough then i would miss some call logs.
This is unacceptable as the data is needed for all kind of management
reports as well as other areas of a web application.

I think i'll speak to the web service provider to see if i can get them to
add some new API's. I think they might if they knew i was writing a DOS app!!

Thanks again for all you help,