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DB2 on z/OS by Mind Map: DB2 on z/OS
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DB2 on z/OS

System Objects

DB2 Directory(DSNDB01)

The DB2 directory contains information that DB2 uses during normal operation. The directory consists of a set of DB2 tables that are stored in table spaces in system database DSNDB01. Each of the table spaces that are listed in the following table is contained in a VSAM linear data set. You cannot access the directory by using SQL, although much of the same information is contained in the DB2 catalog, for which you can submit queries. The structures in the directory are not described in the DB2 catalog.

DB2 Catalog(DBNDB06)

DB2 maintains a set of tables that contain information about the data that DB2 controls. These tables are collectively known as the catalog. The catalog tables contain information about DB2 objects such as tables, views, and indexes. When you create, alter, or drop an object, DB2 inserts, updates, or deletes rows of the catalog that describe the object. The DB2 catalog consists of tables of data about everything defined to the DB2 system, including table spaces, indexes, tables, copies of table spaces and indexes, and storage groups. The system database DSNDB06 contains the DB2 catalog. When you create, alter, or drop any structure, DB2 inserts, updates, or deletes rows of the catalog that describe the structure and tell how the structure relates to other structures.

DB2 Log

DB2 records all data changes and other significant events in a log. If you keep these logs, DB2 can re-create those changes for you in the event of a failure or roll the changes back to a previous point in time. DB2 writes each log record to a disk data set called the active log. When the active log is full, DB2 copies the contents of the active log to a disk or magnetic tape data set called the archive log. You can choose either single logging or dual logging. v A single active log contains up to 93 active log data sets. v With dual logging, the active log has twice the capacity for active log data sets, because two identical copies of the log records are kept.


The bootstrap data set (BSDS) is a VSAM key-sequenced data set (KSDS). This KSDS contains information that is critical to DB2, such as the names of the logs. DB2 uses information in the BSDS for system restarts and for any activity that requires reading the log. Specifically, the BSDS contains: v An inventory of all active and archive log data sets that are known to DB2. DB2 uses this information to track the active and archive log data sets. DB2 also uses this information to locate log records to satisfy log read requests during normal DB2 system activity and during restart and recovery processing. v A wrap-around inventory of all recent DB2 checkpoint activity. DB2 uses this information during restart processing. v The distributed data facility (DDF) communication record, which contains information that is necessary to use DB2 as a distributed server or requester. v Information about buffer pools. Because the BSDS is essential to recovery in the event of subsystem failure, during installation DB2 automatically creates two copies of the BSDS and, if space permits, places them on separate volumes.

Buffer Pool

Buffer pools are areas of virtual storage in which DB2 temporarily stores pages of table spaces or indexes. Access to data in this temporary storage is faster than accessing data on a disk. When an application program accesses a row of a table, DB2 retrieves the page that contains the row and places the page in a buffer. If the required data is already in a buffer, the application program does not need to wait for it to be retrieved from disk, so the time and cost of retrieving the page is reduced. Buffer pools require monitoring and tuning. The size of buffer pools is critical to the performance characteristics of an application or group of applications that access data in those buffer pools.

Default DB(DSBDB04)

Work File DB(DSBDB07)

Use the work file database as storage for processing SQL statements that require working space, such as that required for a sort. The work file database is used as storage for DB2 work files for processing SQL statements that require working space (such as the space that is required for a sort), and as storage for created global temporary tables and declared global temporary tables. DB2 creates a work file database and some table spaces in it for you at installation time. You can create additional work file table spaces at any time. You can drop, re-create, and alter the work file database or the table spaces in it, or both, at any time. In a non-data-sharing environment, the work file database is named DSNDB07. In a data sharing environment, each DB2 member in the data sharing group has its own work file database. You can also use the work file database for all temporary tables.

System Connections








Address Spaces


ssnmMSTR performs a variety of system-related functions. - Thread Mgmt - Log Mgmt - Checkpoint - Trace


- Locking Mgmt


ssnmDBM1 provides most database-related services. Most large storage areas reside above the 2 GB bar in the ssnmDBM1 address space. With 64-bit virtual addressing to access these storage areas, DB2 can scale to extremely large sizes. - SQL processing - Buffer Mgmt - User DB Mgmt - Catalog/Directory Mgmt


ssnmDIST provides support for remote requests.


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.

Performance Monitoring and Tuning


Data Structure

Data Integrity