jchen21 commented on pull request #5689:
URL: https://github.com/apache/geode/pull/5689#issuecomment-731472883


   When compacting oplogs offline, it creates a new krf and persists 
`totalCount` with `0` in Oplog constructor. Then live entries are copied from 
old oplogs to the new oplog. `totalCount` of the new oplog is updated during 
this process. However, the updated `totalCount` is not persisted. Its persisted 
value is still `0`, although the oplog is non-empty after compaction. 
   
   During recovery, the value of `totalCount` is recovered from krf as `0`.  
`totalLiveCount` is incremented as the oplog is recovered. `totalCount` remains 
`0`. Therefore, if `totalCount` == 0 and `totalLiveCount` > 0, no compaction is 
needed. Since this condition shows that offline compaction is just done before 
recovery.


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