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What is the architecture of DB2?

What is the architecture of DB2?

That is a short question that requires a very long answer. The following overview is adapted from my book, DB2 Developer's Guide (http://www.craigsmullins.com/cm-book.htm). Conceptually, DB2 is a relational database management system. Physically, DB2 is an amalgamation of address spaces and intersystem communication links that, when adequately tied together, provide the services of a relational database management system.

Each DB2 subsystem consists of from three to five tasks started from the operator console. Each of these started tasks runs in a portion of the CPU called an address space.

The first address space is the DBAS, or Database Services Address Space. DBAS provides the facility for the manipulation of DB2 data structures. The default name for this address space is DSNDBM1. (The address spaces may have been renamed at your shop.) This component of DB2 is responsible for the execution of SQL and the management of buffers, and it contains the core logic of the DBMS. The DBAS consists of three components, each of which performs specific tasks: the Relational Data System (RDS), the Data Manager (DM), and the Buffer Manager (BM).

Next is the SSAS, or System Services Address Space. SSAS coordinates the attachment of DB2 to other subsystems (CICS, IMS/TM, or TSO). SSAS is also responsible for all logging activities (physical logging, log archival, and BSDS). DSNMSTR is the default name for this address space. DSNMSTR is the started task which contains the DB2 log.

The third address space required by DB2 is the IRLM, or Intersystem Resource Lock Manager. The IRLM is responsible for the management of all DB2 locks (including deadlock detection). The default name of this address space is IRLMPROC.

The next DB2 address space, DDF, or Distributed Data Facility, is optional. The DDF is required only when you want distributed database functionality. If your shop must enable remote DB2 subsystems to query data between one another, the DDF address space must be activated.

The final address space (or series of address spaces) is devoted to the execution of stored procedures and user-defined functions. These address spaces are known as the Stored Procedure Address Spaces, or SPAS. If you're running DB2 V4, only one SPAS is available. For Under DB2 V5 and later releases, however, if you're using the MVS WorkLoad Manager (WLM), you can define multiple SPAS. These five address spaces contain the logic to handle all DB2 functionality effectively.

This response is continued.

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