Defining a Database Name Table › Overview

Overview

A database name table is used to:

• Group multiple segments under one name for processing as a single database or dictionary
• Group multiple segments under one name for maintenance operations
• Define a default dictionary for both online and local mode processing
• Identify the database to be accessed by a rununit when no database name is provided by the application or its runtime environment
• Identify the database groups to which database requests can be dynamically routed in a parallel sysplex environment

Contents of a Database Name Table

A database name table contains the definition of one or more database names defined with a CREATE DBNAME statement. Database names group segments together for processing as a single database or dictionary. Each database name definition consists of its name and the identification of one or more segments containing data required by applications accessing the named database. Additional options associated with a database name influence the processing of non-SQL applications. These options permit:

• Translating subschema names at runtime
• Restricting access to specified subschemas
• Binding a run unit to areas with a mixture of page groups and maximum records per page values

A database name table also includes a set of DBTABLE mapping rules used to identify the database or dictionary to be accessed if none is specified at runtime. These rules identify the database name to be accessed when a rununit binds to a given subschema. Every database name table must include at least one DBTABLE mapping rule to identify the default dictionary.

In a parallel sysplex environment, a database name table may also define one or more database groups defined with a CREATE DBGROUP statement. A database group represents a named collection of central versions that can service a given set of database requests. Any central version whose database name table includes the database group to which a request is directed is a member of that group and is eligible to service that request. The request will be dynamically routed to one of the CVs in the database group based on CPU availability.

Note: For more information about DBGROUPs and dynamic routing, see the CA IDMS System Operations Guide.

Grouping Segments Together

The purpose of a database name is to group multiple segments together for use as a single database. Segment grouping is primarily used for defining dictionaries and non-SQL defined databases. The following example illustrates how database names can be used for defining test and production employee databases.

Each database name consists of two segments, one containing employee data and one containing project data. The production database EMPDB, contains segments EMPSEG and PROJSEG; the test database TESTDB, contains segments TEMPSEG and TPROSEG.

         Database name table ALLDBS

         ┌─────────────────────────────────────────────┐
         │    ┌──────────────────────────────────┐     │
         │    │Database name EMPDB               │     │
         │    │                                  │     │
         │    │     Segment EMPSEG               │     │
         │    │     Segment PROJSEG              │     │
         │    │                                  │     │
         │    └──────────────────────────────────┘     │
         │                                             │
         │    ┌──────────────────────────────────┐     │
         │    │Database name TESTDB              │     │
         │    │                                  │     │
         │    │     Segment TEMPSEG              │     │
         │    │     Segment TPROSEG              │     │
         │    │                                  │     │
         │    └──────────────────────────────────┘     │
         └─────────────────────────────────────────────┘

Utility Use Only Database Names

Database names can also be created simply as a means of referring to a group of segments even though no application will ever access the segments together. Creating such database names can simplify administration since certain commands, such as DCMT QUIESCE, can operate by DBNAME. In order to avoid warning messages caused by such arbitrary groups of segments, you can specify FOR UTILITY USE ONLY when defining the DBNAME.

Note: For more information about the types of warnings that may be reported, see 6.2.6, “Conflicting Names” and 6.2.7, “Mixed Page Groups and Maximum Records Per Page”.