You can use files in production libraries while you are in debug mode, and therefore need to prevent the files from being unintentionally updated.
To prevent database files in production libraries from being unintentionally changed, you can specify UPDPROD(*NO) or default to *NO on the Start Debug (STRDBG) command. Then, only files in test libraries can be opened for updating or adding new records. If you want to open database files in production libraries for updating or adding new records or if you want to delete members from production physical files, you can specify UPDPROD(*YES).
You can use this function with the library list. In the library list for your debug job, you can place a test library before a production library. You should have copies of the production files that might be updated by the program being debugged in the test library. Then, when the program runs, it uses the files in the test library. Therefore, production files cannot be unintentionally updated.