Joined: 06 Jun 2008 Posts: 8154 Location: East Dubuque, Illinois, USA
You reorganize a VSAM file by unloading the data from it, deleting, defining, and reloading the data into it. This is done to remove CI/CA splits, which slow down data access. As to how frequently you need to do it, that depends entirely upon the circumstances. A file that has no CI/CA splits isn't going to benefit from a reorganization. A file that splits hundreds or thousands of times a day probably needs a reorganization every night. You have to balance the resources required to reorganize the file versus the additional access required by a file with splits.
Where a file is getting a high level of CI/CA splits, consideration should be given to adjusting the FREESPACE values. Be aware that the CA freespace should likely be a lower percentage than CI freespace. This is because the freespace is cumulative - i.e. given 100 cyls, CA FSPC of 20 leave 80% available for CIs (80Cyl). If CI FSPC is also 20, then only 80% of that remaining space is available (64Cyl) for initial load of data. Overall, that means 36% of the data area is unused after re-organisation.
CA split only occurs where a CI split requires use of another CA, so these are less frequent than CI splits.