Managing Connections
Applications that use HTTP to connect to data resources can use the .NET Framework's ServicePoint and ServicePointManager classes to manage connections to the Internet and to help them achieve optimum scale and performance.
The ServicePoint class provides an application with an endpoint to which the application can connect to access Internet resources. Each ServicePoint contains information that helps optimize connections with an Internet server by sharing optimization information between connections to improve performance.
Each ServicePoint is identified by a Uniform Resource Identifier (URI) and is categorized according to the scheme identifier and host fragments of the URI. For example, the same ServicePoint instance would provide requests to the URIs https://www.contoso.com/index.htm and https://www.contoso.com/news.htm?date=today since they have the same scheme identifier (http) and host fragments (www.contoso.com). If the application already has a persistent connection to the server www.contoso.com, it uses that connection to retrieve both requests, avoiding the need to create two connections.
ServicePointManager is a static class that manages the creation and destruction of ServicePoint instances. The ServicePointManager creates a ServicePoint when the application requests an Internet resource that is not in the collection of existing ServicePoint instances. ServicePoint instances are destroyed when they have exceeded their maximum idle time or when the number of existing ServicePoint instances exceeds the maximum number of ServicePoint instances for the application. You can control both the default maximum idle time and the maximum number of ServicePoint instances by setting the MaxServicePointIdleTime and MaxServicePoints properties on the ServicePointManager.
The number of connections between a client and server can have a dramatic impact on application throughput. By default, an application using the HttpWebRequest class uses a maximum of two persistent connections to a given server, but you can set the maximum number of connections on a per-application basis.
Note The HTTP/1.1 specification limits the number of connections from an application to two connections per server.
The optimum number of connections depends on the actual conditions in which the application runs. Increasing the number of connections available to the application may not affect application performance. To determine the impact of more connections, run performance tests while varying the number of connections. You can change the number of connections that an application uses by changing the static DefaultConnectionLimit property on the ServicePointManager class at application initialization, as shown in the following code sample.
// Set the maximum number of connections per server to 4.
ServicePointManager.DefaultConnectionLimit = 4;
[Visual Basic]
' Set the maximum number of connections per server to 4.
ServicePointManager.DefaultConnectionLimit = 4
Changing the ServicePointManager.DefaultConnectionLimit property does not affect previously initialized ServicePoint instances. The following code demonstrates changing the connection limit on an existing ServicePoint for the server https://www.contoso.com to the value stored in newLimit.
Uri uri = new Uri("https://www.contoso.com/");
ServicePoint sp = ServicePointManager.FindServicePoint(uri);
sp.ConnectionLimit = newLimit;
[Visual Basic]
Dim uri As New Uri("https://www.contoso.com/")
Dim sp As ServicePoint = ServicePointManager.FindServicePoint(uri)
sp.ConnectionLimit = newLimit