JUBUILD

Documents says:
JUBUILD works by transferring everything from a source directory hierarchy to a destination directory hierarchy, including subdirectories, pipes, flat files, distributed files and standard hashed files. Hashed files are converted from Universe to jBASE via a low level data migration module jufimp which is called either directly or indirectly depending on the size of the Universe hashed file. If it looks like the file will take a long time, i.e. it’s size is greater than PhantFileSize, then the job is put into a queue for background processing."

My questions are:
which file holds the records already been process ?
Which file holds the records were on the queue (size is greater than PhantFileSize)?

What does below file contains:
MIG.CONTROL
MIG.PHANTS
MIG.ACCOUNT
MIG.FILES