z/VSE: 45 Years of Progress - z/VM - IBM

arise, DBAs and application support
staff find themselves in the unenviable
position of considering a database redesign—usually
accompanied by an
extended application outage.
By prioritizing these issues in order of
their importance during the database
design phase, we can greatly reduce the
need for re-design after implementation.
Following are some common postimplementation
issues broken into sections
corresponding to the laws of
database administration (see “The Laws
of Database Administration” by
Lockwood Lyon, which appeared in the
October/November 2006 issue of
z/Journal, at www.mainframezone.com/
applications-and-databases/the-lawsof-database-administration).
Database
design practices that respect the first
law (data must be recoverable) come
first, followed by the remaining laws in
priority order.
Design for Recoverability
Recoverability means the ability to
recover a specific subset of application
data to a specified point in time. Reasons
for such a recovery vary from largescale
disasters (such as loss of a data
center) to undoing incorrect data
updates caused by an application.
In the case of disaster recovery, the
DBA must take into consideration that
total recovery time begins with physical
data/media recovery, availability of the
operating system, tape and recovery
resources (if applicable), and DB2 subsystem
or group recovery. Once DB2 is
available, any utilities in-flight may need
to be terminated and in-doubt threads
resolved. In a data sharing environment,
failed members may hold retained locks.
Once these items are addressed, the
DBA can review remaining application
data recovery issues.
Database design must account for
the required application data recovery
service level for all scenarios.
Are there new tables in the design?
Many of these must be added to recovery
scripts. Are tables being expanded,
or will there be an increase in data or
transaction volume? Perhaps this will
affect the total recovery time; the DBA
may need to revisit existing recovery
procedures. Figure 1 lists some things to
consider during database design that
may affect the DBA’s ability to recover
the application’s data.
Design for Availability
After recovery, data availability is
the next highest priority. Here, the DBA
Figure 1: Database Design Considerations Related to Application Data Recovery
Figure 2: Horizontal Partitioning Strategies and Their Usefulness
Figure 3: Vertical Partitioning Strategies and Their Usefulness
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