Major Description
The HTable client cannot retry a scan operation in the getRegionServerWithRetries code path.
This will result in the client missing data. This can be worked around using hbase.client.retries.number to 1.
The whole problem is that Callable knows nothing about retries and the protocol it dances to as well doesn't support retires.
This fix will keep Callable protocol (ugly thing worth merciless refactoring) intact but will change
ScannerCallable to anticipate retries. What we want is to make failed operations to be identities for outside world:
N1 , N2 , F3 , N3 , F4 , F4 , N4 ... = N1 , N2 , N3 , N4 ...
where Nk are successful operation and Fk are failed operations.