Hi Pranas.
Spoke to the Product Manager:
We're not clear what you mean by "RMS cluster joins". RMS DOC has a concept of clusters (from the doc) ... The CLUSTER_SIZE attribute is output from the Analyze/RMS_File utility (ANALYZE/RMS_FILE), which returns the actual value of the disk cluster size to EDIT/FDL for use during an Optimize script.
Or are you talking about a multi field join on what might be a multiple fields with separate keys or a multiple fields with a single key?
We'd need to have more details (i.e., your .mas and .acx files) and preferably an actual test data files to understand if we do or don't have a similar test and verify if you can do what it is you are attempting. Our product group has some doubts that we actually have a test like this, but we need to see a sample to verify. If you don't have a sample data file that you don't mind sending, then we need the creation FDL. (You can privately message me this info. if you'd like.) Also, if you are sending a .DAT RMS file, it needs to be in a BACKUP saveset, or the attributes will be lost.
If we do not have a similar test and what you want to do actually works (or can be fixed so it works), then we can add your sample (provided the datafiles aren't too large).
You should provide more info as a start, but in the end you will likely have to open a case with
Tech Support to provide files so we can review.
Hope this helps,
Monica