UDS-D enables an application program to access the databases of multiple DB configurations. The application program is only aware of the subschema name, so UDS-D must know whether the subschema is located in a local or remote DB configuration.
This information is made available by means of an input file, which is created by the database administrator for each DB configuration in which distributed transactions are to be started. This input file is used by UDS-D to create the so-called distribution table. This input file and the distribution table created from it contain the following assignments:
Subschema: Database
Database: Configuration and
Configuration: Host processor and password
The distribution table is placed by UDS-D in the distribution pool so that the distribution component in the user task can access it during the session. The distribution table may also include local databases and local subschemas, so the same distribution tables can be provided for all DB configurations. If the distribution tables are large, it is advisable to place the local databases and subschemas at the start of the input file to ensure good response times for local transactions.
Databases and subschemas that are not described in the distribution table are treated as local.
Remote databases and subschemas that are not described in the distribution table cannot be accessed by a local application program.