Data preservation allows you to control how data appears in your
target database when there are changes to the data structures or metadata.
Whenever change commands are generated that involve CREATE and DROP table
statements, that data will likely need to be preserved. You can create the
necessary export and import commands by using the data preservation options
in DB2® Change Management Expert.
DB2 Change Management Expert allows
you to preserve your data from the Change Commands page in the Deployment
Script Editor.
Data preservation is useful in the following situations:
- When you drop a table
- When you drop a table, you might want to store the data from that table
in a file for future use. DB2 Change Management Expert automatically
generates this file, but this functionality can be disabled.
- When you create a new table
- When you create a new table, you might want to populate the table with
data from an existing data file. You can map the data that you want to export
from one table and import into another table by using the Generate Change
Commands wizard.
After you generate the change commands, you can manually
edit the change commands to import the data from the data file. If you edit
the change commands manually, verify that the import commands are added to
the change command list after the other change commands.
- When you perform a destructive change
- If you rename a table by using a DROP and CREATE statement, you will need
to export the data in that table and then import it. DB2 Change Management Expert automatically
creates data preservation entries, one with the export commands to drop the
table (old name), and another with the import commands to create the table
(new table name). You can use the pair function to combine these two entries
into one. This way, the export and import commands have the same data file.
You can toggle the Customize field to make data preservation entries read-only
or customizable. When an entry is customizable, additional wizard pages that
assist with the customization of export and import commands are available.
Customization of the data preservation change commands is necessary to correctly
deploy certain changes.
Restriction: When you generate change commands, the default data
preservation entries are always regenerated. Previously generated data preservation
commands are not brought in as part of rerunning the Generate Change Commands
wizard.
To skip the data preservation process, uncheck the Enable data
preservation option in the Generate Change Commands wizard.
Advanced data preservation techniques
Advanced data
preservation techniques include:
- Dropping columns
- Dropping columns can be easily managed by creating a new data preservation
entry. One approach is to accept the default during export customization.
For example, if you enable undo by selecting that check box, an export command
will automatically be generated. However, when you customize your import commands,
you must map the exported columns to the imported columns.
- Adding NOT NULL columns
- Adding NOT NULL columns is simple provided that the column has a default
value. If there is no default value, customize the export command by using
the Customize Export Command page of the Generate
Change Commands wizard or use the Generate Data Migration wizard.
- Normalizing tables
- There are many strategies for normalizing a table. These techniques range
from creating new normalized tables and transforming them in the database
to transforming during the export and import of data.
Moving data between databases
Moving data between databases requires exporting data from one database
and importing data into another. DB2 Change Management Expert supports
data migration with the Generate Data Migration wizard.
LOAD Providers
DB2 Change Management Expert now
supports LOAD commands as well as IMPORT commands. You can specify the default
load provider for the data load operations by using the preferences page ().
You can change the load provider for a particular load operation by selecting Data
Load Provider from the drop-down menu under Mapping Details on
the Mapping Tables page. DB2 Change Management Expert also
supports the IMPORT provider. You can specify the command options for all
providers on the Specify File Information page of the Generate
Change Commands wizard.For more information about the DB2 LOAD and the DB2 IMPORT
commands, see the IBM® DB2 Command Reference.

UNLOAD providers
Data Unload Providers generate different types of unload commands. The
following table shows the three different providers that DB2 Change Management Expert supports
and the corresponding file formats for the EXPORT commands:
Table 1. Supported unload providers and their corresponding file
formatsUnload provider |
Corresponding file format for EXPORT commands |
EXPORT_DEL |
DEL data file format |
EXPORT_IXF |
IXF data file format |
HPU |
HPU unload commmands |
In order to deploy the generated HPU unload commands, the DB2 High Performance
Unload (HPU) for Multiplatforms (or Workgroups) product must be installed. Attention: DB2 Change Management Expert supports
the DB2 High
Performance Unload (HPU) for Multiplatforms (or Workgroups) product to unload
your data. However, note that HPU is a separately priced tool and must be
installed before setting the DB2 Change Management Expert option
for Data Unload Provider to HPU. If you set the Data Unload Provider to HPU
and HPU is not installed, the generated unload commands will fail.
You
can unload data using either the HPU command or a DB2 EXPORT command. You can specify the
default unload provider on the preferences page by selecting . If you select
HPU as the default provider, then DB2 Change Management Expert generates
HPU commands for all of the unload operations. You can override this behavior
for any particular unload operation by selecting a different Data
Unload Provider on the Mapping Tables page of the Generate
Change Commands wizard. For more information about High Performance
Unload, see the IBM DB2 High Performance Unload for Multiplatforms and Workgroups
User's Guide V3.1.
For more information about EXPORT commands,
see the IBM DB2 Command
Reference.

Using REORG commands
DB2 Change Management Expert now
supports the REORG maintenance command. DB2 Change Management Expert can
generate REORG commands for you through the Generate Change Commands wizard.
When a table space is altered, DB2 Change Management Expert generates
a REORG command for all of the indexes and tables contained within the table
space. When a table is altered, DB2 Change Management Expert generates
a REORG command for the indexes defined on the table. REORG commands are optional. 
Using the Auto CAST function
If the data types of the import and export columns are mismatched, DB2 Change Management Expert resolves them automatically
by adding a CAST column function in the SELECT clause of the EXPORT statement.
This can be done by selecting Auto Cast on the Customize
Export Commands page of the Generate Change Commands wizard. There is another
option, Default Query that allows you to revert to
the default SELECT clause. Restriction: If you make any additional
changes to the SELECT clause, they will be lost when you select the Auto
Cast or Default Query options.
