keith-turner commented on PR #3640:
URL: https://github.com/apache/accumulo/pull/3640#issuecomment-1683156059

   > I was thinking it could be better to use the prev row column for each 
tablet instead since we track the previous row
   
   That probably would be cleaner.  That is what happens when using Ample it 
buffers the entire row and uses that column to constuct the extent for the 
tablet.   Ample can also optionally check the linking of tablets when reading 
them.
   
   >  The manager is doing the metadata updates for the merge inside of 
TabletGroupWatcher and I am wondering is it possible for the table or tablets 
being modified to be split concurrently during the merge or compactions to 
happen? 
   
   There should not be anything else writing to the tablets metadata because of 
the following combination of factors.
   
    1. When a tablet is hosted, only the tablet server its assigned to will 
update its metadata
    2. When a tablet is not hosted or assigned, only the manager will update 
its metadata
    3. The merge operation unassigns the tablets before updating them, so 
tablet servers should not longer be doing any updates
    4. The merge operation gets a write lock on the table that prevent any 
other operations from running in the manager that would update the tables.
   
   These are some basics of Accumulo's current concurrency model.  Its very 
different in the elasticity branch.
   
   
   


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