rsts/dd_mismatch/action is a SAP Parameter attribute which is used to control Define action for data dictionary checks in TemSe information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Defines step(s) to take if inconsistencies arise between the DB/DDIC
structures and the kernel C structures.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.