sodonnel commented on pull request #2268:
URL: https://github.com/apache/ozone/pull/2268#issuecomment-846933140


   @GlenGeng Thanks for the review. I will go ahead and commit this one, and 
raise a new Jira for issue 2.
   
   I think you are correct, in that we may need a monotonically increasing 
sequence number in the datanode, plus maybe some locking in the DN to guarantee 
the contents of the FCR.
   
   The hard part, is figuring out what to do with that information on SCM. I 
wonder if we need to attach the "report sequence number" to every replica in 
SCM. Then we can say:
   
   * The FCR is has sequence 100, and it does not have container 1001.
   * 1001 is in SCM, but added by ICR sequence 101.
   * Right now, the FCR processing would remove container 1001, but with the 
sequence we could ensure it does not remove anything created by a newer 
sequence number.
   
   However this approach adds a new field to every replica which would have a 
memory overhead, so we need to try to think of a better way.


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