Designing .NET Applications

The guidelines in this section will help you to optimize system performance when designing .NET applications.

Managing Connections

Connection management is important to application performance. Optimize your application by connecting once and using multiple statement objects, instead of performing multiple connections. Avoid connecting to a data source after establishing an initial connection.

You can improve performance significantly with connection pooling, especially for applications that connect over a network or through the World Wide Web. Connection pooling lets you reuse connections. Closing connections does not close the physical connection to the database. When an application requests a connection, an active connection is reused, thus avoiding the network I/O needed to create a new connection.

Pre-allocate connections. Decide what connection strings you will need to meet your needs. Remember that each unique connection string creates a new connection pool.

Once created, connection pools are not destroyed until the active process ends or the connection lifetime is exceeded. Maintenance of inactive or empty pools involves minimal system overhead.

Connection and statement handling should be addressed before implementation. Spending time and thoughtfully handling connection management improves application performance and maintainability.

Opening and Closing Connections

Open connections just before they are needed. Opening them earlier than necessary decreases the number of connections available to other users and can increase the demand for resources.

To keep resources available, explicitly Close the connection as soon as it is no longer needed. If you wait for the garbage collector to implicitly clean up connections that go out of scope, the connections will not be returned to the connection pool immediately, tieing up resources that are not actually being used.

Close connections inside a finally block. Code in the finally block always runs, even if an exception occurs. This guarantees explicit closing of connections. For example:

try

{

   DBConn.Open();

… // Do some other interesting work

}

catch (Exception ex)

{

   // Handle exceptions

}

finally

{

   // Close the connection

   if (DBConn != null)

      DBConn.Close();

}

If you are using connection pooling, opening and closing connections is not an expensive operation. Using the Close() method of the data provider's Connection object adds or returns the connection to the connection pool. Remember, however, that closing a connection automatically closes all DataReader objects that are associated with the connection.

Using Statement Caching

A statement cache is a group of prepared statements or instances of Command objects that can be reused by an application. Using statement caching can improve application performance because the actions on the prepared statement are performed once even though the statement is reused multiple times over an application’s lifetime.

A statement cache is owned by a physical connection. After being executed, a prepared statement is placed in the statement cache and remains there until the connection is closed.

Caching all of the prepared statements that an application uses might appear to offer increased performance. However, this approach may come at a cost of database memory if you implement statement caching with connection pooling. In this case, each pooled connection has its own statement cache that may contain all of the prepared statements that are used by the application. All of these pooled prepared statements are also maintained in the database’s memory.

Using Commands Multiple Times

Choosing whether to use the Command.Prepare method can have a significant positive (or negative) effect on query execution performance. The Command.Prepare method tells the underlying data provider to optimize for multiple executions of statements that use parameter markers. Note that it is possible to Prepare any command regardless of which execution method is used (ExecuteReader, ExecuteNonQuery, or ExecuteScalar).

Consider the case where an ADO.NET data provider implements Command.Prepare by creating a stored procedure on the server that contains the prepared statement. Creating stored procedures involves substantial overhead, but the statement can be executed multiple times. Although creating stored procedures is performance-expensive, execution of that statement is minimized because the query is parsed and optimization paths are stored at create procedure time. Applications that execute the same statement multiples times can benefit greatly from calling Command.Prepare and then executing that command multiple times.

However, using Command.Prepare for a statement that is executed only once results in unnecessary overhead. Furthermore, applications that use Command.Prepare for large single execution query batches exhibit poor performance. Similarly, applications that either always use Command.Prepare or never use Command.Prepare do not perform as well as those that use a logical combination of prepared and unprepared statements.

Using Native Managed Providers

Bridges into unmanaged code, that is, code outside the .NET environment, adversely affect performance. Calling unmanaged code from managed code causes the data provider to be significantly slower than data providers that are completely managed code. Why take that kind of performance hit?

If you use a bridge, your code will be written for this bridge. Later, when a database-specific ADO.NET data provider becomes available, the code must be rewritten; you will have to rewrite object names, schema information, error handling, and parameters. You'll save valuable time and resources by coding to managed data providers instead of coding to the bridges.