Overview of ALTER

By automating and simplifying the change process, ALTER enables you to deal effectively with the demands of a constantly changing Db2 environment. ALTER uses an Interactive System Productivity Facility (ISPF) interface.

ALTER is designed for the single Db2 system that is beginning to encounter complex challenges. As the need for more change management functions develops, as with multiple Db2 subsystems, you can upgrade from ALTER to Change Manager.

ALTER enables you to automate the following common tasks:

• Create, modify, and drop data structures within a Db2 subsystem
• Create new data structures by using existing data structures as templates
• Determine the dependencies on changed objects and preserve those dependencies and their associated data
• Migrate data structures and data within a subsystem or from one Db2 subsystem to another subsystem
• Analyze the impact of changes by validating the changes against the Db2 catalog
  If conflicts are detected, ALTER notifies you through error messages and warnings.
• Implement a least-cost strategy for performing changes
  You can group your changes to minimize the work that is required to execute them.
• Import data definition language (DDL) files and create the objects
• Perform space estimation for table spaces and indexes
• Provide passive management of authorizations, plans, and packages
• Provide automatic data conversion for changes to column attributes
• Handle requirements for data set allocations
• Specify global structure changes when migrating objects

ALTER provides full management support for the following Db2 data structures:

• Storage groups (stogroups)
• Databases
• Table spaces
• Tables
• Check constraints
• Foreign keys
• Triggers
• Indexes
• Unique constraints
• Views
• Synonyms
• Aliases

When you use ALTER to specify changes for any of these data structures, the product automatically propagates the changes to any dependent objects. For example, if you change the name of a table, ALTER creates a corresponding change in the indexes, synonyms, and other dependent objects that reference the table under its former name.

ALTER uses BMC or IBM utilities in worklists when required. By using installed BMC utilities instead of IBM utilities, you can significantly enhance the performance of executing ALTER worklists. BMC utilities run faster, provide additional features, and might reduce the number of steps in a worklist.

You can use the following BMC utilities with ALTER:

• CHECK PLUS for DB2
• BMC AMI Check for Db2
• BMC AMI Copy for Db2 
• LOADPLUS for DB2
• BMC AMI Load for Db2
• BMC AMI Recover for Db2
• REORG PLUS for DB2
• BMC AMI Reorg for Db2
• SNAPSHOT UPGRADE FEATURE
• UNLOAD PLUS for DB2
• BMC AMI Unload for Db2
• BMCSTATS utility of DASD MANAGER PLUS for DB2
• BMC AMI Stats for Db2

The utilities must support the same version of Db2 as ALTER or Change Manager. For more information, see the utility product’s documentation.

Data structure changes

Within a Db2 subsystem, an application’s data structures need continual modification and extension because of changes in application requirements, performance tuning, and expanding uses of data.

ALTER enables you to make changes to data structures in an easy, reliable, and automated way. You can efficiently perform changes while preserving data and, if necessary, convert the data to match the changes. ALTER also enables you to rebuild dependent objects and then propagate changes into those dependent objects. Without ALTER, these tasks can be extremely difficult to perform.

Data structure migration

If you have multiple Db2 subsystems, you might need to copy data structures from one subsystem to another.

Most Db2 sites have separate subsystems for development, testing, and production. Many sites support multiple production systems, some of which are local and some remote.

ALTER offers the following functionality to simplify data structure migration:

• Generates SQL CREATE statements from the sending subsystem for use on the receiving subsystem
• Applies CREATE statements on the receiving subsystem
• Moves data from the sending subsystem to the receiving subsystem

When you migrate an application’s data structures, ALTER assumes that these data structures do not yet exist on the receiving subsystem. ALTER cannot create new data structures if data structures with the same names already exist on the receiving subsystems.

Data structure importation

You use ALTER to process DDL files that are received from an external subsystem and apply the changes to your subsystem.

The Import component converts these data structure definitions into change requests that are grouped together in a work ID. ALTER stores these change requests in the Change Definition (CD) tables.

Space estimation

ALTER provides space estimation capability that enables you to determine the amount of space that a table space or index will require based on the object definitions and their estimated usages.

You can specify estimates of the number of rows in the table, and the average length of the rows. ALTER will use this information to project the number of tracks, cylinders, or blocks that are required to allocate the data set for that object.