Daniel Roudnitsky created HBASE-28560:
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             Summary: Region quotas: Split/merge procedure rollback can lead to 
inaccurate account of region counts
                 Key: HBASE-28560
                 URL: https://issues.apache.org/jira/browse/HBASE-28560
             Project: HBase
          Issue Type: Bug
    Affects Versions: 3.0.0-beta-2
            Reporter: Daniel Roudnitsky
            Assignee: Daniel Roudnitsky


When region quotas are enabled, HMaster keeps an in memory account of region 
counts through NamespaceStateManager. Region counts in NamespaceStateManager 
are incremented/decremented at the beginning stages of split/merge procedures, 
in SPLIT_TABLE_REGION_PRE_OPERATION/MERGE_TABLE_REGIONS_PRE_MERGE_OPERATION 
before any region is offlined. If the split/merge procedure gets rolled back 
after the region count change in NamespaceStateManager is made, the split/merge 
procedure rollback does not revert the region count change in 
NamespaceStateManager to reflect that the expected split/merge never succeeded. 
This leaves NamespaceStateManager with an inaccurate account of the number of 
regions, believing that there are more/less regions than actually exist.  



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