IAM DYNAMIC REORG Increases Application Availability and Provides a Significant Reduction
in CPU and Elapsed Time.

The IAM Dynamic Reorganization feature provides two capabilities that dramatically reduce the amount of time IAM data sets are unavailable for online processing. The first is a reorganization technique that reduces wall clock and CPU time to reorganize IAM data sets, particularly those with a significant amount of overflow area usage. The second is the ability to carry out the high performance reorganization while the data set continues to be available for CICS online system processing. This process then temporarily closes the file to CICS, quickly performs the updates to the new reorganized copy that occurred during the reorganization, and reopens the file to CICS. The data set is unavailable to CICS only for the few seconds that it takes to close, update, rename, and reopen. Read and writes are slightly delayed during this time.

24x7 Availability

IAM/RLS and RLS Journaling are additional features in the base IAM product that can help you
achieve 24x7.

Performance Example

To demonstrate the benefits, a benchmark was done on an IAM file with an alternate index versus the equivalent VSAM file. The file had following characteristics:

• Record Length of 325 bytes • Key Length of 43 bytes • Alternate Key Length of 52 bytes
• Loaded with 9,000,000 records, followed by a batch job insertion of 500,000 records
• At time of reorganization, it had 9,506,269 records

The results are shown below for the different reorganization scenarios indicating the amount of time the data set would be unavailable to CICS:

IAM REORG Comparison

Dynamic REORG Benchmark

Whether you choose to use the new reorganization facility in a manner similar to the existing reorganization processing of closing the file under CICS, or the Dynamic Reorg process that reduces data set unavailability to a few seconds, the new reorganization process provides substantial benefits.