Forum post about Persistence, IEventActivity, Transactions, and Correlation

re: Forum post about Persistence, IEventActivity, Transactions, and Correlation

hba — Tue, 01 Aug 2006 22:50:39 GMT

Hello I'm new to windows workflow and workflow architecture in general.

I've been going through the tutorials and have an architectural/design question about the correlated communication scenario.

Does it make sense to:
a) Use Multiple workflow instances or
b) Use a single instance with a communication service that is enabled through correlations.

For example, in an order processing scenario where they may be thousands of orders going through the system per hour; does it make sense to have thousands of workflow instances (a one to one relationship between orders and workflow instances) or only one workflow instance?

Thanks in advance.

re: Forum post about Persistence, IEventActivity, Transactions, and Correlation

ntalbert — Wed, 02 Aug 2006 03:29:00 GMT

hba,

The answer to your question actually depends on your scenario. Just like object oriented programming, you should model your workflows in the way that is most confortable for you. So, consider the following:

Online Shopping Cart
In this scenario there are thousands of completely independent orders going at any given time. You should opt for a 1 to 1 correspondence in this case where a single workflow instance manages a single order.

This is fine to do with respect to resources because workflow does not use resources in the same way as typical programs. The normal workflow instance will be idle more than 95% of its lifetime ... they are characterized by short bursts of work to figure out what to do next with large periods of waiting for more stimulus from the outside world. Additionally, an idle workflow does not consume any threads and depending on your host an idel workflow might not even take up any space in memory.

What this boils down to is that in most scenarios you don't have to optimize for a minimal number of workflow instances which gives you the freedom to implement your solution in the way that makes the most sense.

Business to Bussiness Supply
You can imagine a company that might have a few large customers and each customer has several concurrent orders in place. There are a few different ways to model this. First, you might not care to include the overall customer management as part of your workflow solution and this could simply degenerate to the shopping cart scenario above - a bunch of unrelated orders.

Another option, however, would be to model a relationship with a customer as a single workflow which also manages each of the orders the customer currently has in the works. Still another option is to break this down further by having the customer management workflow spawn other workflows to take care of each order giving you a heirarchy of flow.

Once again, the point is that you should use the solution that you are most comfortable with and that best captures the spirit of the process which you are trying to model.

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