joshelser commented on pull request #3488:
URL: https://github.com/apache/hbase/pull/3488#issuecomment-884452513


   > I guess why we create it in tmp directory first is because the 
CatalogJanitor? Not sure. But theoretically, since we do not need to scan the 
filesystem to get all the regions for a table when opening it, I do not think 
we need to introduce a Strategy to handle both cases, just change the code to 
write it to the final place. This could be done on master and branch-2.
   
   > I guess hbck recovery could be a problem for the default tracking, if the 
resulting merging/splitting region dir got already created in the FS, fails 
before completing the operation then vanishes from meta
   
   That's a fun thought. Things like rebuilding meta from the filesystem 
suddenly become dubious. I think we also know that building and HBCK which is 
capable of identifying a "split-in-progress" is hard. Like Duo say, we can put 
the Region in the "correct" place and it will just be used once meta is updated.
   
   What if we had some special marker in the Region which we cleaned up after 
it was opened the first time? HBCK could look for that marker and know that if 
we find a Region on the FS with this marker that isn't in meta, we should be 
able to just ignore/delete it (as a split/merge which was in-flight).


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