Availability Guide for Application Design

Designing Applications for Change
Availability Guide for Application Design—525637-004
10-36
Recompiling or Execution-Time Name Resolution for
Data Definition Changes
Recompiling or Execution-Time Name Resolution for Data
Definition Changes
Once an SQL program is installed and running on a production system, it might
become necessary to perform logical changes to the data schema, such as adding a
column to a table or creating an index; or to perform physical changes such as moving
a partition to another disk. In addition to the data availability issues discussed under
Physically Reconfiguring the Database on page 10-28, you should also consider the
effects that these Data Definition Language (DDL) changes can have on invalidating
your execution plans.
You can eliminate or minimize application downtime due to invalid execution plans by
making use of similarity checks.
Figure 10-6. Increasing Application Availability During SQL Program Upgrade
Development
System
Production
System
Catalog
Table T2
Install the program using
REGISTERONLY ON
Enable the similarity check for
the table using ALTER TABLE
Change DEFINE to refer to
Table T2
Execute the program
(No automatic recompilation
if similarity check passes)
Compile the program with
SQL
using CHECK INOPERABLE
PLANS
Set DEFINE to refer to
Table T1
Table T1
Catalog
VST906.vdd