Multiplexed Connections

Many traditional nonthreaded SQL client applications use multiple database connections to perform work for a single user. Each database connection establishes a separate network connection to the database server.

The multiplexed connection facility for the database server provides the ability for one network connection in the database server to handle multiple database connections from a client application to this database server.

When a nonthreaded client uses a multiplexed connection, the database server still creates the same number of user sessions and user threads as with a nonmultiplexed connection. However, the number of network connections decreases when you use multiplexed connections. Instead, the database server uses a multiplex listener thread to allow the multiple database connections to share the same network connection.

To improve response time for nonthreaded clients, you can use multiplexed connections to execute SQL queries. The amount of performance improvement depends on the following factors:

• The decrease in total number of network connections and the resulting decrease in system CPU time

  The usual cause for a large amount of system CPU time is the processing of system calls for the network connection. Therefore, the maximum decrease in system CPU time is proportional to the decrease in the total number of network connections.

• The ratio of this decrease in system CPU time to the user CPU time

  If the queries are simple and use little user CPU time, you might experience a sizable reduction in response time when you use a multiplexed connection. But if the queries are complex and use a large amount of user CPU time, you might not experience a performance improvement.

  To get an idea of the amounts of system CPU time and user CPU times per virtual processor, use the onstat -g glo option.

To use multiplexed connections for a nonthreaded client application, you must take the following steps before you bring up the database server:

1. Add a NETTYPE entry to your ONCONFIG file and specify SQLMUX in the connection_type field.

   The NETTYPE SQLMUX configuration parameter tells the database server to create the multiplex listener thread. When you specify SQLMUX in the connection_type field of the NETTYPE configuration parameter, the other NETTYPE fields are ignored.

2. Set the multiplexed option (m=1) in the client sqlhosts file or registry for the corresponding dbservername entry.

   For more details on the ONCONFIG file NETTYPE entry and the sqlhosts entry, see your IBM Informix: Administrator's Guide.

3. On Windows platforms, you must also set the IFX_SESSION_MUX environment variable.

For more information on restrictions on the use of multiplexed connections, see the IBM Informix: ESQL/C Programmer's Manual and your IBM Informix: Dynamic Server Administrator's Guide.