[GitHub] [accumulo] keith-turner commented on pull request #3640: WIP - no chop merge proof of concept

["keith-turner (via GitHub)" <gi...@apache.org>]

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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