Takeover OPEN

The OPEN ACB macroinstruction also allows an alternate application to take over an active application that has enabled persistence. VTAM® requires that the opening and original applications have the same ACBNAME.

When a takeover occurs, the takeover application program connects to VTAM and restores sessions, even though the original application has not failed. The takeover application program opens its ACB (PARMS=(PERSIST=YES)), and VTAM schedules the TPEND exit of the original application program and closes the application program. If the original application program does not have a TPEND exit, VTAM closes it without any notification. Any sessions are placed in the recovery pending state. The alternate application program must restore or terminate these sessions.

An application can indicate that it can be the target of an SNPS takeover attempt by specifying PARMS=(FORCETKO=ALL), or PARMS=(FORCETKO=SINGLE), on a SETLOGON OPTCD=PERSIST macroinstruction invocation. In addition, by default, an application is considered to support SNPS takeover attempts, but not MNPS forced takeover attempts, until the application indicates otherwise. If the original application has not indicated its support of an SNPS takeover request, and a takeover OPEN ACB is processed, then the OPEN ACB will be failed with an OPEN error code X'7C'.