UDR Connection (Server)

A C UDR cannot establish a connection to the database server. It must run within an existing session, which a client application begins when it establishes a client connection. To obtain access to an existing session, a UDR establishes a UDR connection. A UDR uses the mi_open( ) function (with NULL-valued pointers for all arguments) to establish a UDR connection. A UDR can have one or more UDR connections to the session.

Because a C UDR cannot establish a connection, it never begins a session. Instead, it inherits the context of an existing session from the SQL statement that invokes the UDR. This SQL statement executes within a session that the client application has begun. Therefore, the UDR is already connected to a particular database server and has access to a database that has already been opened. The UDR is also inside the current transaction.

A UDR connection provides access to the session context. This session context persists across all invocations of a UDR instance because a UDR connection has the duration of an SQL command. That is, the mi_open( ) function and its corresponding mi_close( ) function do not necessarily have to be called from within the same invocation of the UDR but they do have to be called within the same instance. For more information, see Establishing a UDR Connection (Server).