Duo Zhang commented on HBASE-20182:

Don't we skip the offlined parent as it is? Where do you see us not doing this?
No, we don't... Otherwise the UT above will not fail... We only scan one row, 
and if it is offine or split parent then we just throw out an exception... So 
here we need to continue until we find out that the current region is out of 

We can introduce a new family but where would it go? In each of the daughters? 
Or in each of the parents for the merge?
I think just keep them in the same row as now, but in a new family?

> Can not locate region after split and merge
> -------------------------------------------
>                 Key: HBASE-20182
>                 URL: https://issues.apache.org/jira/browse/HBASE-20182
>             Project: HBase
>          Issue Type: Bug
>          Components: Region Assignment
>            Reporter: Duo Zhang
>            Priority: Blocker
>             Fix For: 2.0.0
>         Attachments: HBASE-20182-UT.patch
> When implementing serial replication feature in HBASE-20046, I found that 
> when splitting a region, we will not remove the parent region, instead we 
> will mark it offline.
> And when locating a region, we will only scan one row so if we locate to the 
> offlined region then we are dead.
> This will not happen for splitting, since one of the new daughter regions 
> have the same start row with the parent region, and the timestamp is greater 
> so when doing reverse scan we will always hit the daughter first.
> But if we also consider merge then bad things happen. Consider we have two 
> regions A and B, we split B to C and D, and then merge A and C to E, then 
> ideally the regions should be E and D, but actually the regions in meta will 
> be E, B and D, and they all have different start rows. If you use a row 
> within the range of old region C, then we will always locate to B and throw 
> exception.

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