WCF最佳性能设置

Question

Hi i am creating an API using WCF. My question can be broken down into two seperate ones

1) I have quite a few calls, for instance i have calls relating to the customer, products, orders, employees.

My question is should all this go into one public interface class eg

public interface IRestService
public class RestService : IRestService

Or should I have one for each call eg

public interface ICustomer
public class Customer : ICustomer

public interface IProducts
public class Products: IProducts

2) If you have an API which will be accessed by tens of thousands of users and thousands of users concurrently, how would you set up, what will your web config settings be for instance in terms of throttling. Also what setting would you give your InstanceContextMode , or ConcurrencyMode . Finally what type of binding would it be, bearing in mind websites and mobile phones can access the api.

Answer 1

1. If you really have few operations, single service can be used. Generally services are logical collection of related operations but the number of operations should be limited. Usually if your service have more than 20 operations you should think about refactoring.

2. Do you plan to use REST service? I guess you do because of your first interface example. In such case you need WebHttpBinding (or similar custom binding) with default InstanceContextMode ( PerCall ) and ConcurrencyMode ( Single ) values. Only other meaningful combination for REST service is InstanceContextMode.Single and ConcurrencyMode.Multiple but it will create your service as singleton which can have impact on your service implementation. My rule of thumb: Don't use singleton service unless you really need it.

3. Throttling configuration is dependend on your service implementation and on performance of your servers. What does thousands concurrent users really mean for you? Processing thousands of requests concurrently requires good server cluster with load balancer or hosting in Azure (cloud). All is also dependend on the speed of processing (operation implementation) and size of messages. The correct setting for MaxConcurrentInstances and MaxConcurrentCalls (should be same for PerCall instancing) should be revealed by performance testing. Default values for service throttling have changed in WCF 4.

Answer 2

For the sake of good practice, I would break up the API into separate interfaces so you have the option of splitting them into separate implementations in the future. You can still have just one service class implement all of the interfaces, like this:

public class RestService : ICustomer, IProducts, IOrders

However, it sounds as if you'd probably want to make them separate implementations anyway.

In terms of concurrency settings, ask yourself what resources need to be used on each call. If your service class's constructor can be written without any lengthy startup, then use PerCall. If you need to initialize expensive resources, then I'd recommend InstanceContextMode.Single with ConcurrencytMode.Multiple and make sure you write thread-safe code. Eg: make sure you lock() on any class properties or other shared resources before you use them.

Database connections would not count as "expensive to initialize", though, because ADO will do connection pooling for you and eliminate that overhead.

Your throttling settings will be revealed by testing, as Ladislav mentions. You'd want to stress-test your service and use the results to get an idea of how many machines you'd need to service your anticipated load. Then you'll need a dedicated load balancer to route requests as either round-robin, or something that checks the health of each server. Load balancers can be set up to GET a "systemhealth.asp" page and check the results. If you return an "OK" then that machine stays in the pool, or can be temporarily removed from the pool if it times out or returns any other status.

Your binding would need to be WebHTTPBinding for REST. BasicHTTPBinding is meant for SOAP interfaces and doesn't support [WebGet], for example.

If it doesn't have to be a REST service, then you can get a bit more performance by using NetTcpBinding.