Smart, fast online reorganization keeps your IMS databases running 24x7
from CCR2, Issue 10 - 2007
Janet Leblanc, IMS Tools Consultant, was interviewed for this article.
Many IMS databases need to run 24x7. That doesn’t leave much time for database reorganization, which is required for top performance. With IBM IMS Online Reorganization Facility for z/OS V1.2, you can shrink your outage window to just a minute or two – and stay on schedule.
|
Database administrators (DBAs) recognize that update activity will cause a database to gradually degrade, since user additions and deletions have a scattering effect. As empty space reserved for new data gradually becomes scarce, the database may not find convenient storage places for new data and will instead spread the data across multiple locations or simply add it to the end.
Ignoring the need for reorganizations can dramatically raise the costs of running IMS applications. When applications try to access unorganized data, the additional I/Os slow the database and the applications that depend upon it. Many businesses outsource their datacenters or charge resource use back to individual departments. Increased resource time results in higher costs.
Reorganizing a database puts it back in order for fast retrieval and re-introduces the free space needed for future updates.
Traditionally, reorganization required taking the database offline for hours. But banks, airlines, shipping companies and many other industries need systems up all the time for business operations and customer Web access.
Today, fewer and fewer IMS databases can be taken off line for more than a brief time without negatively impacting the business. IBM IMS reorganization tools let you get your database back in shape quickly.
Is it time to reorg your IMS database?
You can determine if your database needs to be reorganized using several statistics:
- Declining FREESPACE, which indicates the database may soon expand.
- The presence of dataset extents, which reveal data is being added to the end of the database, often because it lacks free space in the middle.
- The index portion of a VSAM data set keeps having control interval control area (CI/CA) splits.
- The data portion of a VSAM data set’s high-use relative byte address (RBA) continues to increase.
- Roots begin to stop randomizing to the home block in a (P)HDAM database.
Although the above statistics are the most frequently used to determine when a database needs to be reorganized, the true indicator is application performance. If the application doesn’t access the areas of the database that require additional I/Os, performance won’t be affected.
IMS Performance Analyzer for z/OS allows you to compare current application performance statistics to those collected immediately after an earlier reorganization. This data provides the best indicator of when to initiate reorganization.
Maintain the highest availability with online reorganization
When reorganization is needed, most businesses want it to take as little time as possible. IBM offers two high performance reorganization utilities: IMS Parallel Reorganization for z/OS and IMS Online Reorganization Facility for z/OS.
IMS Parallel Reorganization lets you unload and reload the data and rebuild your database in parallel very quickly while it is offline (Figure 1). This solution allows you to decrease the reorganization time and offers the option of permitting read access to the data during the reorganization.
Figure 1: Parallel reorganization system flow
IMS Parallel Reorganization uses the following IBM IMS tools:
IMS Online Reorganization Facility for z/OS, on the other hand, reorganizes data sets in one step with minimal database availability impact (Figure 2). It provides all the necessary reorganization procedures (unload, reload, prefix resolution, prefix update, secondary index building and image copy) in one simple step. It also provides optional pointer checking and database description block (DBD) changes.
Figure 2: Online reorganization data flow
Because it uses a shadow set of the database data sets, Online Reorganization lets you update the database concurrently during the reorganization. All changes are captured and applied to the reorganized data in the shadow data sets.
Once the reorganization is complete, the database is taken offline during the TAKEOVER phase for just a couple of minutes to alter the shadow datasets to the original database data set names.
What’s more, you can precisely schedule the brief takeover window. If the scheduled timeframe is missed, flexible options let you automate appropriate actions, such as delaying takeover until the next scheduled outage window or implementing takeover sooner.
IMS Online Reorganization Facility for z/OS V1.2 dynamically detects the existence of the following IBM IMS tools and uses them accordingly:
If any of these tools are not available on your system, IMS Online Reorganization Facility will use the base IMS utilities instead.
Harness IBM technology for your own IMS applications
IBM’s multi-purpose IMS High Performance tools can also be used independently, providing added value.
Both the Unload and Reload utilities offer an application programming interface (API). An API enables an IMS Batch DL/I application program, that reads an IMS database sequentially, to use the IMS High Performance Unload utility engine for greater speed. Similarly, using the IMS High Performance Load API can boost the performance of an application that needs to load a database.
Using these APIs improves both the elapsed time and the CPU time for the application. In a controlled test environment*, IBM found that the Unload API delivered a 69 percent elapsed time improvement and a 45 percent improvement in CPU time, while the Load API delivered an even greater 89 percent elapsed time improvement and 61 percent improvement in CPU time.
Gain more from tool integration
IBM IMS Tools also work well together to help you extract maximum value. Both Online Reorganization Facility and IMS Parallel Reorganization integrate with many utilities, and the integration continues throughout the IBM utility portfolio. For example, IMS Database Recovery Facility for z/OS integrates with IMS Index Builder to automatically rebuild your primary and secondary indexes during a recovery.
In addition, this summer IBM introduced the IMS Tools Knowledge Base for z/OS, a vehicle to an enriched IMS Tools experience that provides:
- A single platform for report output
- History for analysis
- History of actions
- A platform to share information across IMS tools
- A pathway to autonomics.
The IMS Tools Knowledge Base will continue to evolve. In addition to capturing IMS Tools reports and statistics, IBM envisions the Knowledge Base as a hub for autonomic capabilities that could, for example, sidestep an unnecessary reorganization.
Gain top performance 24x7
Database reorganization is important for efficient database access and application performance. IMS Online Reorganization Facility for z/OS V1.2 reduces downtime from hours to a minute or two and increases database administration productivity and efficiency with a single-step reorganization process without manual intervention.
*IMS & IMS Tools performance study results contained in this document were obtained in a controlled lab environment; therefore, the results that can be obtained in another operating environment might vary significantly.
For more information:
|
