Availability Guide for Change Management

Making Application Subsystem Changes Online
Availability Guide for Change Management–125506
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NonStop SQL/MP Changes You Can Perform Online
NonStop SQL/MP Changes You Can Perform Online
When you make changes to a NonStop SQL/MP database, you do not need to shut down
the NonStop system, and most changes can be made without affecting NonStop
SQL/MP application availability. This flexibility is because of a number of underlying
factors:
•
The relational structure of the NonStop SQL/MP database provides database
independence, which ensures that objects can be added or altered in the database
with little or no effect on existing applications.
•
The NonStop SQL/MP database structure is described in an active data dictionary.
NonStop SQL/MP automatically updates the dictionary when database objects are
created, altered, or dropped.
•
NonStop SQL/MP versioning lets you maintain distributed nodes at different release
levels. You can migrate to new release levels without moving data or recompiling
SQL programs.
•
The NonStop TM/MP product protects the database and keeps track of database
activity. The NonStop TM/MP product is described later in this section.
The following subsections describe common NonStop SQL/MP changes.
Adding, Dropping, and Altering Objects
Because the NonStop SQL/MP database structure is described in an active data
dictionary, the operation of existing applications can usually continue regardless of
database changes. You can typically add, alter, or drop database objects, including
tables, indexes, views, constraints, and collations, without interrupting your applications.
Reorganizing a Database
Reorganizing a NonStop SQL/MP database can involve reloading data, adding partitions
to a table or index, splitting or moving all or part of a partition to access additional space
or improve I/O performance, or compacting a file to improve disk usage.
Any change you make to your database organization will have some impact on
application availability. Under some conditions, availability will be very high; under
other conditions, availability will be lower. Using the WITH SHARED ACCESS option
with certain SQL statements can help you reduce the impact of database reorganization
on application availability:
The WITH SHARED ACCESS option maximizes application availability by allowing
read and write access to data during certain data definition language (DDL) operations
for all but a relatively brief period at the end of the operation. SQL statements that
support the WITH SHARED ACCESS option include CREATE INDEX and the move
partition form of the ALTER INDEX and ALTER TABLE statements. For example, you
Note. A CREATE INDEX operation that uses the WITH SHARED ACCESS option increases
availability. If the WITH SHARED ACCESS option is not specified, only read access on the
base table is allowed. A CREATE INDEX operation with the WITH SHARED ACCESS option
has the same brief downtime as is associated with reorganization.