Maintain an ACM using RC/Migrator

Products

• RC/Migrator for DB2 for z/OS

Issue/Introduction

Can RC/Migrator (RCM) be used to automate and maintain Alternate Catalogs (ACMs)? In particular can RCM be used to perform the following functions:

• Create the ACM shadow tables from the DSNDB06 catalog tables.
• Transfer the definitions of a new ACM to an existing ACM on another Db2 subsystem.
• Update an existing ACM without completely dropping and recreating it (by altering the objects according to new definitions).

Resolution

RC/Migrator can be used to maintain an ACM but it's use does have limitations as follows:

• Create the ACM shadow tables from the DSNDB06 catalog tables.

This approach for creating ACM databases and their shadow tables is not recommended. By design an ACM is created with shadow tables for a subset of the catalog tables; not all. Using RC/Migrator to create the ACM from DSNDB06 would create some tables not supported by ACM. We therefore only recommend using the ACM Maketab option to create an ACM database and shadow tables. The catalog tables that ACM supports are listed here.

• Transfer the definitions of a new ACM to an existing ACM on another Db2 subsystem.

A Compare strategy, comparing at the database level, can be used to compare the newer ACM to the older ACM and to generate the DDL and utilities to update the target ACM objects. However, this can only be done when the source and target ACMs are on the same Db2 version and function level (this is a must). There is one manual requirement when doing this. Once the new shadow table definitions have been created in the target subsystem, then the user must access ACM Mapping Services to map any new catalog tables to the new shadow tables. 

• Update an existing ACM without completely dropping and re-creating it (by altering the objects according to new definitions).

This can be done using a Compare strategy, comparing at the database level. The analysis will generate the required DDL, including ALTER statements to, for example, add new columns to the target shadow tables. Again this approach should only be used between subsystems of a similar Db2 version and function level.