Client affinities for Db2 on Linux, UNIX, and Windows systems

Client affinities is a client-only method for providing automatic client reroute capability.

Client affinities is available for applications that use CLI, .NET, or Java™ (IBM® Data Server Driver for JDBC and SQLJ type 4 connectivity). All rerouting is controlled by the driver.

Client affinities is intended for situations in which you need to connect to a particular primary server. If an outage occurs during the connection to the primary server, you need to enforce a specific order for failover to alternate servers. You should use client affinities for automatic client reroute only if automatic client reroute that uses server failover capabilities does not work in your environment.

As part of configuration of client affinities, you specify a list of alternate servers, and the order in which connections to the alternate servers are tried. When client affinities is in use, connections are established based on the list of alternate servers instead of the host name and port number that are specified by the application. For example, if an application specifies that a connection is made to server1, but the configuration process specifies that servers should be tried in the order (server2, server3, server1), the initial connection is made to server2 instead of server1.

Failover with client affinities is seamless, if the following conditions are true:

• The connection is not in a transaction. That is, the failure occurs when the first SQL statement in the transaction is executed.
• There are no global temporary tables in use on the server.
• There are no open, held cursors.

When you use client affinities, you can specify that if the primary server returns to operation after an outage, connections return from an alternate server to the primary server on a transaction boundary. This activity is known as failback.