Eliminate window of missing Data
--------------------------------

                 Key: HBASE-4485
                 URL: https://issues.apache.org/jira/browse/HBASE-4485
             Project: HBase
          Issue Type: Sub-task
            Reporter: Amitanand Aiyer
            Assignee: Amitanand Aiyer


After incorporating v11 of the 2856 fix, we discovered that we are still having 
some ACID violations.

This time, however, the problem is not about including "newer" updates; but, 
about missing older updates
that should be including. 

Here is what seems to be happing.


0 - Scanner starts scanning.

0 - MemStore.snapshot is called.

    Scanner has access to kvHeap and snapshot

1-  Flush takes place. 
     1.1 KV's in the snapshot are written to the disk.
     1.2 HFile is ready. 

2   Store.updateStoreFiles() deletes the old snapshot.
    
     2.1 updateReaders will not be called until the end of the columnFamily 
seek.

3  For a brief window of time, scanner does not have access to certain 
KeyValues.
   a) Scanner has no longer access to the snapshot because it is flushed to the
disk. 
   b) It does not yet have access to the HFile because the updateReaders was
not called yet.
        

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