How and Why Databases are Reorganized
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Administration of IMS full function and Fast Path databases can have a
significant impact on the overall performance and usability of critical
business applications. Databases must be recognized to modify the database
schema so that physical disk space can be reclaimed and to ensure acceptable
database performance by facilitating physical adjacency of segments within a
record as well as across records.
Over time, as information is added, updated, and deleted, a database
becomes physically disorganized, decreasing operating efficiency.
More I/O operations are needed to retrieve a segment and its dependents
when they are physically disorganized than when they are physically adjacent
to one another. When this occurs, response time slows noticeably with a
corresponding decrease in end-user productivity.
Physical database reorganization involves placing each root segment
together with its dependent segments into one block (or into adjacent blocks
if they do not fit into a single block). Any secondary indexes for the
reorganized database must be rebuilt, and local relationships pointers between
databases must be resolved and updated. A structure change such as adding or
deleting segment types is also a reason for reorganizing a database.
Reorganization can be painful for a number of reasons. With traditional
reorganization, utilities data is not available during the process, which
means lost revenue as well as lost productivity of your employees. The lack of
IMS expertise in many IT centers causes reorganization to be executed
incorrectly or not at all.
Before reorganizing your database, your company should decide on a database
maintenance cycle. You should also have a plan process in place. A plan
process involves researching and making decisions about the tools and
techniques that you will use to implement your maintenance strategy. The idea
is to determine which tasks and goals are necessary and then to find the tools
that are best designed to help you carry out that plan. You also must then
examine the techniques to use for the gather, analyze, and execute processes
of your strategy. Key considerations may include identifying the specific data
elements that you must collect about your environment and databases,
formulating a method of analysis, developing a monitoring schedule, and
designing a system of rules that tell you when and how to react to the
The gather process involves collecting and managing information about your
environment and databases. You must build and run the jobs to collect data.
You also must manage the storage of the data that is gathered, which includes
performing regular backups, purging data according to established retention
schedules, and recovering data when necessary.
The gather process provides all information on which you base your
analysis. You must collect key elements about the state of each database. You
need to know about any events that occurred in your system that may affect the
databases. While you must ensure that the data which is gathered is current,
you also need historical details about your databases. Using the historical
details you can identify and chart data trends.
The analyze process involves organizing and interpreting the gathered data.
You must process the data into meaningful and manageable reports. You must
build and run jobs to generate the reports. Finally, you must read, compare,
and interpret the reports.
The analyze process identifies problems with your databases. Because it
would be impractical if not impossible to review reports for thousands of
databases manually, the analyze process must be efficient and consistent. You
need a method of analysis that pinpoints specific database problems and
delivers repeatable results.
The execute process involves taking action to correct problems that were
found during the analysis. You must decide which solutions to execute and then
build and run the jobs. You also must monitor the jobs and review job output.
The execute process is important because the overall health and performance of
your database depends on taking appropriate action at the appropriate time.
You must execute solutions that correct as many problems with as few of
resources as possible.
Last, repeat all processes. Database administration processes are cyclical.
When solutions have been executed to correct problems that were reported by
the analysis, the cycle begins anew.
About the Author
Stephen J. Richards has 25 years experience in Data Management and
Information Technology. This information is provided as a public service by Neon
Enterprise Software, a leading provider of
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Article Published/Sorted/Amended on Scopulus 2008-05-16 23:47:03 in Computer Articles