VSAM does not ensure read integrity across splits for non-RLS access to a data set with cross-region share options 2, 3, and 4. If the application requires read integrity, the application must ensure it. When KSDS control-interval (CI) and control-area (CA) splits move records from one CI to another CI, the writer cannot invalidate the data and index buffers for the reader. This can result in the reader not seeing some records that were moved.

VSAM RLS can ensure read integrity across splits. It uses the cross-invalidate function of the coupling facility to invalidate copies of data and index control intervals in buffer pools other than the writer's buffer pool. This invalidation ensures that all VSAM RLS readers, CICS® and non-CICS, are able to see any records moved by a concurrent CI or CA split. On each GET request, VSAM RLS tests the validity of the buffers, and if invalid, refreshes the buffers from the coupling facility or DASD.