The internal resource lock manager (IRLM) is delivered as an integral part of IMS, but you do not have to install or use it unless you need to perform block-level or sysplex data sharing. IRLM is also the required lock manager for DB2 UDB for z/OS.

The IRLM address space is started before the IMS control region with the z/OS START command. If the IMS start-up parameters specify IRLM, the IMS control region connects to the IRLM that is specified on startup and does not complete initialization until the connection is successful.

Typically, one IRLM address space runs on each z/OS system to service all IMS subsystems that share the same set of databases. For more information on data sharing in a sysplex environment, see:

• IMS in the Parallel Sysplex: Volume I: Reviewing the IMSplex Technology
• IMS in the Parallel Sysplex: Volume II: Planning the IMSplex
• IMS in the Parallel Sysplex: Volume III: IMSplex Implementation and Operations

Recommendation: Do not use the same IRLM address space for IMS and DB2 UDB for z/OS because the tuning requirements of IMS and DB2 are different and conflicting. The IRLM code is delivered with both IMS and DB2 UDB for z/OS and interacts closely with both. Therefore, you might want to install the IRLM code for IMS and DB2 UDB for z/OS separately (that is, in separate SMP/E zones) so that you can maintain release and maintenance levels independently. Installing the IRLM code separately can be helpful if you need to install prerequisite maintenance on IRLM for one database product because doing so does not affect the use of IRLM by the other product.