Identifying failed snapshots ?

     Hello,

     I have a master table with an associated snapshot log. There are
     multiple (simple) snapshots defined against this master.

     What is the easiest way to identify those snapshots that have NOT
     successfully used the   log (rows within) ? At this point I don't care
     why, it could be a failure of scheduling issue.

     Oracle's documentation states that the rows in the log are NOT deleted
     until ALL the snapshots have used them. This implies that the "master"
     knows which shnpshots are "interested" in the data and their status.
     Is this information available to me ?

     Thank you (in advance)
     Ken F.