How and Why Databases are Reorganized

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 analysis.

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.