Oracle Tuxedo Application Runtime for Batch takes care of the Database context usage:

• Initialization: If a COBOL program is executed (m_ProgramExec) using the -b option, the runtime command, runb, connects it to the database according to the MT_DB_LOGIN environment variable . It must have the correct value (user name, password and Oracle instance, at least "/"). It can be used in the TuxJES Security Configuration file and specified when submitting jobs or set as an environment variable. If the configuration file is not specified, the environment variable MT_DB_LOGIN value is used.
• Termination: Depending on the program return code, the Batch Runtime executes a COMMIT (if program return code is less than MT_PROG_RC_ABORT) or a ROLLBACK (if program return code is greater than or equal to MT_PROG_RC_ABORT), then disconnects from the database.