Andrey Elenskiy created HBASE-24273:
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             Summary: HBCK's "Orphan Regions on FileSystem" reports regions 
with referenced HFiles
                 Key: HBASE-24273
                 URL: https://issues.apache.org/jira/browse/HBASE-24273
             Project: HBase
          Issue Type: Bug
          Components: hbck2
    Affects Versions: 2.2.4
         Environment: HBase 2.2.4

Hadoop 3.1.3
            Reporter: Andrey Elenskiy


This issue came up after merging regions. MergeTableRegionsProcedure removes 
the parent regions from hbase:meta and creates HFile references in child region 
to the old parent regions. Running `hbck_chore_run` right after the 
`merge_region` will show the parent regions in "Orphan Regions on FileSystem" 
until major compaction is run on child region which will remove HFile 
references and cause Catalog Janitor to clean up the parent regions.

There are probably other situations which can cause the same issue (maybe 
region split?)

Having "Orphan Regions on FileSystem" list parent regions and suggest to 
"_hbase completebulkload_" is dangerous in this case as completing bulk load in 
this case will lead to stale HFile references in child region which will cause 
it's OPEN to fail because referenced HFile doesn't exist.

Figuring out these things for database administrators is tedious, so I think it 
would be reasonable to not consider regions with referenced  HFiles to be 
orphans (or maybe could give an extra hint saying that it has referenced 
HFiles).



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