[GitHub] [hadoop-ozone] hanishakoneru commented on pull request #1480: HDDS-4315. Use Epoch to generate unique ObjectIDs

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hanishakoneru commented on pull request #1480:
URL: https://github.com/apache/hadoop-ozone/pull/1480#issuecomment-706275207


   Thank you @linyiqun and @prashantpogde for the reviews. 
   
   Agree that setting aside 16 bits for epoch doesn't work for both the epoch as well as the transaction ids. 16 bits would not be enough to cover restarts and 40 bits might not be enough for transaction ids. 
   The new proposal is to have only 2 bits set aside for epoch. For non-Ratis OM, the transactionIndex will be saved in DB with every sync operation. When OM is restarted, this transactionIndex will be read from DB so that new transactions do not have clashing indices.
   The epoch would let us distinguish objects created before and after this upgrade. This would help if someone needs to fix the duplicate objectIDs in existing clusters. 
   
   Thank you @bharatviswa504 and @prashantpogde for the offline discussion.


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