Safeguards

Compressed data should not be accessed by application programs when CA Compress is not active, because user programs will experience abends or other problems due to unexpected data.

This exposure is not great for sequential data sets, principally because update in place is not supported, and so access for update while CA Compress is not up simply results in a valid uncompressed data set. Support for sequential data sets using the SUBSYS parameter offers no protection, but customers seldom experience this problem, especially if they use FDTs created by the IUI, which enable CA Compress to distinguish between compressed and uncompressed records if both are present.

For VSAM, however, update in place is commonplace. In contrast to the physical sequential case, keys exist and may not be in the same physical location on the record in compressed and uncompressed records. For these reasons, CA Compress includes the Safeguards facility to protect non-SMS VSAM data sets defined under the CA Compress Transparency.

CA Compress Safeguards protect compressed VSAM data sets from inadvertent access under two conditions:

When the CA Compress subsystem is not active.
When the CA Compress subsystem is being abnormally terminated or shut down by request. If any compressed data sets are being accessed at shutdown time of the CA Compress subsystem, a warning message is issued.

This section contains the following topics:

How Safeguards Protect Data