The following procedures apply if you need to fallback/back out to a previous release When upgrading from:
IDMS r14.1 to r17.0/r18.0
IDMS r15.0 to r17.0/r18.0
IDMS r16.0 to r17.0/r18.0
IDMS r17.0 to r18.0
Perform the following steps to fallback to a previous release (14.1, 15.0, 16.0 or 17.0):
An option to applying the upgrade jobs directly to the files of the current release is to make copies of all the files in the SYSTEM, SYSDIRL and user application dictionaries, the LOG and JOURNAL files. To identify these files the LOOK DMCL command can be used.
The upgrade could then be applied to the copies of these files for testing meanwhile the originals are untouched, and to drop back, you just change your JCL to point to the previous release files, or flip the names.
Usually the LOG and JOURNAL files contain release specific values, so you could create new versions of these, format them, leaving the previous release files alone. When you are done testing the new release you to which you are upgrading simply revert to the previous release files. Alternatively you can offload the JOURNAL and LOG files prior to upgrading, and then format them as the new release. Then to drop back you just format them as the previous release.
If copies were not made of the original files but rather a backup was taken and the upgrade was applied to the original SYSTEM, SYSDIRL and user application dictionaries, restore these files that have been upgraded from a backup taken at the previous release level.
Change all JCL to point to the IDMS load libraries used in the previous release.
Initialize the journal files with the FORMAT utility using the previous release IDMS load libraries.
Offload or initialize the log file using the previous release IDMS load libraries.
If falling back to 14.1, the queue area should be initialized using the 14.1 IDMS load libraries.
The 18.0 SVC is downward compatible and can be used with releases 17.0, 16.0, 15.0 and 14.1.
The 18.0 catalog conversion is compatible with all previous releases up to 14.1. so you can use the 17.0 catalog definitions in the previous release.
User database files are compatible across all releases.
See APAR QI80754 for downward compatibility of ADS dialogs, this also applies to 18.0.