How will I know whether to use IMSHRINK or IMEXPRES for my data compression routines?
IMSHRINK and IMEXPRES are two different compression programs in the Compress for IMS product. IMSHRINK provides a significantly better rate of data compression then IMEXPRES. Either one can be used and the one selected for a database is coded in the IMS DBD (database definition). The reason for choosing IMEXPRES is that it works as is and does not require customization. On the other hand, to setup IMSHRINK requires you to run an analysis of the specific database and based on that analysis, an FDT is generated for that specific database that gives optimal data compression. So, there is work to set up IMSHRINK compression for a specific database.