[GitHub] [ozone] bharatviswa504 commented on pull request #1659: HDDS-4329. Expose Ratis retry config cache in OM.

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bharatviswa504 commented on pull request #1659:
URL: https://github.com/apache/ozone/pull/1659#issuecomment-740095543


   > @bharatviswa504 Thanks for working on this! The changes look good to me.
   > What is the total retry duration for a om client request? I mean what is the retry policy used right now. The cache duration should be >= time for which a request can be retried.
   
   We have 15 retries currently, and if same om is contacted again after failure it doubles the duration. 
   And the double of the time is not for the first round of failovers until we find leader.
   
   And for any other errors, we don't have sleep between retry.
   
   So basically first 3 to find leader OM no time wait. And next, we have detected leader then if it fails over to a new OM, we don't wait. So at best case it would be less than a minute (as for any n/w error we immediately failover). And if we continuously get LeaderNotReady, we try to contact same OM after first round, then it will be (2+4+8+16+ .... +2^12) = 8190 duration, this is the worst time. If OM has taken so long to become Ready after failover and finally in last iteration it became ready.
   
   So, in the worst case, we wait for 150 minutes. But setting at 150 mts, will be taking too much heap on wellbehaved OM. As in most cases, if OM's are up/down the total time if the same OM is not contacted will be less than a minute.


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