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

[GitBox <gi...@apache.org>]

prashantpogde commented on pull request #1480:
URL: https://github.com/apache/hadoop-ozone/pull/1480#issuecomment-705775239


   General comment on using the epoch id that increments with every OM restart. This can get tricky.
    If OM goes in crash restart loop then we have just 2^16 increments available which is 65K attempts. if it takes 1 secs for OM to comeback online we have 65 K secs worth epoch number or 20 hours of crash looping. This is very pessimistic view, it may take several seconds for OM to restart but it does show how
   - 16 bit space can be insufficient for this scheme.
   - epoch need not be dependent on restart based increment. if it increments based on both of the following conditions
       A) OM restart +
       B) some object gets created after epoch id is incremented
      then epoch may last longer. But even then 16 bit looks insufficient. What  if OM creates one object and restarts.


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