Locking protocols

IMS uses locks to isolate the database changes made by concurrently executing programs.

Locking is accomplished by using either the Program Isolation (PI) lock manager or the IRLM. The PI lock manager provides only four locking levels and the IRLM supports eleven lock states.

The IRLM also provides support for feedback only and test locking required, and it supplies feedback on lock requests compatible with feedback supplied by the PI lock manager.