First Time Architecturing?

Question

I was recently given the task of rebuilding an existing RIA. The new RIA that I've designed is based on Silverlight, with a WCF service to connect to MS SQL Server. This is my first time doing something like this, so I'm not sure how to design the entire thing.

Basically, the client can look through graphs of "stocks" (allowing the client to choose different time periods, settings, etc). I've written the whole application essentially, but I'm not sure how to put it together.

The graphs are supposed to be directly based on the database, and to create the datapoints on the graph, some calculations need to be done (not very expensive ones).

The problem I'm having is to decide where to put the calculations (client or serverside? Or half and half?)

What factors should I look for to help me decide where the calculations should be done? And how can I go about optimizing this (caching, etc)?

Obviously this is a very broad subject, so I'm not expecting an immediate answer, but any help/pointing in the right direction/resources would be appreciated.

Answer 1

A few tips for this kind of app.
Put as much logic as possible on the client.
Make the client responsible for session data, making all your server code stateless.
Try to minimize traffic to and from the server (Bigger requests are more efficient than multiple smaller ones) so consolidate requests when possible.

Answer 2

If this project is likely to grow beyond it's current feature set I think it's probably a good idea to perform the calculations client side. This can avoid scaling issues, because you're using all the client side CPUs ratther than you're single, precious server CPU. This does however rely on being able to transfer the required data to the client in an efficient way, otherwise you replace a processor bottleneck with a network bottleneck.

As for caching it depends on your inputs, what variables can users of the client affect? If any of the variables they can alter are discrete (ie they can be a fixed set of values) then they're candidates for caching. For example if a user can select a date range of stock variations to view then that's probably not so useful, if however they can only select a year then you could cache your data sets by year (download each data set to the client and perform your calculation). I'd not worry about caching too much unless you find it's a real performance problem, it'll only make your code more complex, so don't add it until you have proven you need it.

One other thing, if this project is unlikely to be a long term concern then implement the calculations wherever is easiest and fastest, you can revisit if the project becomes more important later on.

Answer 3

Be REALLY REALLY careful about implementing client-side caching. Caching is INSANELY hard to do right while maintaining performance, security and correctness. Note that your DB Server's caching mechanism is already likely to be way better than any local caching mechanism you're likely to implement in less than 2 weeks' effort!

I would urge you to do as much work on the back-end as possible and to limit your client to render the data in a manner that is appropriate for your users. While many may balk at this suggestion, it's based on a number of observations from building many such systems in the past:

• If you're going to filter some of the data returned by your service, you've just wasted thousands of clock cycles shipping data that need never have left your server
• If you're going to sort your data, your DB could have done the sorting for you (often using otherwise idle CPU ticks) while waiting for the data to be read from its disks.
• Your server most likely has more CPU and RAM available than your clients and has a surprising amount of "free time" to use for sorting, filtering, running inline calculations, etc., while its waiting for disks to read sectors etc.

As Roman suggested: Minimize your round-trips between your client and your server as much as possible.

But perhaps most importantly:

1. BEFORE YOU START DESIGNING YOUR SYSTEM, state your performance goals
2. Design what you think will achieve those goals. Try to find bottlenecks in your design, particularly areas where you make blocking calls. Re-design those areas to use async patterns wherever you can.
3. Build your intended solution
4. Measure your actual perforamnce under actual real-world load
5. If you're within your expected performance goals, then you're done.
6. If not, work out where you're spending too long and tune the design of that portion of the system. Goto 3.

Don't try to build the perfect system in one try - chances are that you won't manage it, no matter how hard you try, for a variety of reasons including user expectations, your servers ability to process the required load, your clients' ability to handle the returned data, your network's ability to carry the traffic, etc.

They're a little old now, but I suggest you read through some of the earlier posts at http://blogs.msdn.com/richardt for more thoughts around designing and constructing Service Oriented and distributed systems.