Db2 address spaces in the z/OS environment

Db2 operates as a formal subsystem of z/OS and works efficiently with other z/OS subsystems and components.

A subsystem is a secondary or subordinate system that is usually capable of operating independently of, or asynchronously with, a controlling system. A Db2 subsystem is a distinct instance of a relational DBMS. Its software controls the creation, organization, and modification of a database and the access to the data that the database stores.

z/OS processes are separated into regions that are called address spaces. Db2 for z/OS processes execute in the following z/OS address spaces.

Database services address space (ssnmDBM1)
The database services address space is responsible for accessing relational databases that are controlled by Db2 for z/OS and provides most database-related services. The input and output to database resources is performed on behalf of SQL application programs in this address space. Most large storage areas reside above the 2 GB bar in the database services address space (ssnmDBM1). With 64-bit virtual addressing to access these storage areas, Db2 can scale to extremely large sizes.
System services address space (ssnmMSTR)
The system services address space starts and stops Db2, and controls local access to Db2 for z/OS, and performs various system-related functions.
Distributed data facility (DDF) services address space (ssnmDIST)
The distributed data facility (DDF) services address space (often called the DDF address space) supports network communications with other remote systems and execution of database access requests on behalf of remote users to support distributed database services.
Internal resource lock manager (IRLM) address space (irlmproc)
Db2 uses the IRLM address space to control access to database resources and locking.
WLM-established address spaces
Zero to many address spaces for stored procedures and user-defined functions. WLM-established address spaces are handled in order of priority and are isolated from other stored procedures or user-defined functions that run in other address spaces.
Allied agent address spaces
At least one, possibly several, of the following types of user address spaces:
  • TSO
  • Batch
  • CICS®
  • IMS dependent region
  • IMS control region
  • WebSphere®
Restriction: The REUSASID=YES keyword enables z/OS reusable address space ID capability. In most cases, Db2 address spaces, and all connected address spaces, cannot be started with REUSASID=YES. However, for Java applications that use IBM Data Server Driver for JDBC and SQLJ type 4 connectivity to connect to Db2 data servers, the associated Db2 address spaces can be started with REUSASID=YES.

Db2 works efficiently with other z/OS subsystems and components, such as the z/OS Security Server and the IBM zSystems Parallel Sysplex® environment.

Db2 utilities run in the z/OS batch or stored procedure environment. Applications that access Db2 resources can run within the same z/OS system in the CICS, IMS, TSO, WebSphere, stored procedure, or batch environments, or on other operating systems. These applications can access Db2 resources by using the client/server services of the Db2 distributed data facility (DDF). IBM® provides attachment facilities to connect Db2 to each of these environments.