The ESSS and data spaces

The Environment Services System Services (ESSS) address space is created when the CICSPlex® SM subsystem is created by the first CMAS started after an MVS™ IPL. The ESSS is, in MVS terms, a limited function system address space. Once it is started, it never terminates, but neither does it run. The ESSS serves as an anchor point for the data required to establish the connection between a CMAS and its local MASs. It also serves as the owner of all CICSPlex SM data spaces and cross-memory services resources. The data in the ESSS private area is updated by program call routines provided by ESSS itself. Since the ESSS does not run after initialization, it is very reliable. This reliability helps to ensure that the cross-memory resources and data spaces remain available until CICSPlex SM explicitly deletes them.

CICSPlex SM uses MVS data spaces to store some of its data structures because of the potentially large amount of data involved in managing a CICSplex environment. The size of some data structures is directly related to the number of managed systems, while the size of others is related to the number of interconnected CMASs or the system management options in use (such as real-time analysis or monitoring).

Individual data caches are used by each component that has significant storage requirements. Each logical cache can span more than one data space, but no two caches ever share a single data space. So even a simple CICSplex configuration can cause the allocation of many data spaces. While many data spaces may be created, however, CICSPlex SM uses only as much storage as is actually required for a given configuration.

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