Availability Guide for Application Design

Designing Applications for Change
Availability Guide for Application Design—525637-004
10-38
Changing a NonStop Process Pair
If a DDL change would cause unacceptable automatic recompilations, then you need
to bring down the application to perform SQL compilation. Using the COMPILE
INOPERABLE PLANS compile option, you can enforce the similarity check at compile
time and keep compilation time to a minimum.
If you want your application to endure DDL changes then you must handle potential
open invalidation errors and timeouts.
Changing a NonStop Process Pair
Changing a process that cannot be stopped seems like a contradiction in terms.
However, even a continuously available application will need to be updated or
upgraded. It is possible to change a NonStop process pair without making it
unavailable. Techniques exist to replace:
•
The process itself
Figure 10-7. Increasing Application Availability During DDL Changes
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
reference Table T2
Execute the program
Compile the program
with SQL using CHECK
INOPERABLE PLANS
Catalog
Perform DDL operation
(No automatic recompilation
if similarity check passes)
VST907.vdd