Chapter 10 — Improving Web Services Performance[8]

• Strongly typed. These include .NET types such as double and int, and custom objects such as Employee, Person, and so on. The advantage of using strongly typed parameters is that .NET automatically generates the schema for these types and validates the incoming values for you. Clients use the schema to construct appropriately formatted XML messages before sending them.
• Loosely typed. These parameters use the string type. Note that you should not pass XML documents as string parameters because the entire string then needs to be XML encoded. For example, < and > needs to be converted to &lt and &gt and so on. Instead, you should use either an XmlElement parameter or implement IXmlSerializable. The latter is the most efficient and works well for large data sizes, regardless of which encoding style you use, you should prefer simple primitive types like int, double, and string for Web services parameters. Use of primitive types leads to reduced serialization and automatic and efficient validation by the .NET Framework.

Avoid Maintaining Server State Between Calls

Maintaining per-caller state in memory on the server limits scalability because the state consumes server resources. As an alternative, you can pass state back and forth between the client and Web service. Although this approach enables you to scale your service, it does add performance overhead — including the time taken to serialize, transmit, parse, and de-serialize the state with each call.

Consider Input Validation for Costly Web Methods

If you have a Web method that performs costly and time-consuming processing, consider validating the Web method input before processing it. It can be more efficient to accept the validation overhead to eliminate unnecessary downstream processing. However, unless you are likely to receive invalid input frequently, you should probably avoid schema validation due to the significant overhead that it introduces. You need to assess your specific situation to determine whether or not schema validation is appropriate.

You can validate input data either by using SOAP extensions or by using separate internal helper methods that your Web methods call. The advantage of using SOAP extensions is that they permit you to separate your validation code from your business logic. If there is any schema change in the future, the extension can change independently of the Web method.

Another option is to use the XmlValidatingReader class to perform schema-based validation, as shown in the following code snippet.

[WebMethod]
public void ValidateCreditCard(string xmlCardInfo){
  try
  {
    // Create and load a validating reader
    XmlValidatingReader reader = new XmlValidatingReader(xmlCardInfo,
                                                       
XmlNodeType.Element, null);

    // Attach the XSD schema to the reader
    reader.Schemas.Add(
           "urn:CardInfo-schema",@"http://localhost/Card/Cardschema.xsd");

    // Set the validation type for XSD schema.
    // XDR schemas and DTDs are also supported
    reader.ValidationType = ValidationType.Schema;

    // Create and register an event handler to handle validation errors
    reader.ValidationEventHandler += new ValidationEventHandler(
                                                        ValidationErrors );

    // Process the input data
    while (reader.Read())
    {
    . . .
    }

    // Validation completed successfully
  }
  catch

  { . . .}
}
// Validation error event handler
private static void ValidationErrors(object sender, ValidationEventArgs args)
{
  // Error details available from args.Message
  . . .
}

Consider Your Approach to Caching

You can greatly enhance Web services performance by caching data. With ASP.NET Web services, you can use many of the same caching features that are available to ASP.NET applications. These include ASP.NET output caching, HTTP response caching, and ASP.NET application caching.

In common with any caching solution, your caching design for a Web service must consider issues such as how frequently the cached data needs to be updated, whether or not the data is user-specific or application-wide, what mechanism to use to indicate that the cache needs updating, and so on. For more information about caching with Web services, see the "Caching" section later in this chapter.

Consider Approaches for Bulk Data Transfer and Attachments

You can use the following approaches to optimize the performance of bulk data transfer: