DYNAMIC REORGANIZATION OF IAM DATASETS
Dynamic REORG Increases Application Availability and Provides a Significant Reduction
in CPU and Elapsed Time.
IAM Version 9.3/01, in conjunction with FDRREORG Version 5.4/85 or higher, greatly improves reorganization processing for IAM Enhanced Format Data Sets.
The IAM Dynamic Reorganization feature provides two new capabilities that dramatically reduce the amount of time IAM data sets are unavailable for online processing. The first is a new 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.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:
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.