code: protected String getShardIterator(SequenceNumber sequenceNumber) throws Exception {
  
  		if (isSentinelSequenceNumber(sequenceNumber)) {
  			return getShardIteratorForSentinel(sequenceNumber);
  		} else {
  			// we will be starting from an actual sequence number (due to restore from failure).
  			return getShardIteratorForRealSequenceNumber(sequenceNumber);
  		}
  	}
docs: Returns a shard iterator for the given {@link SequenceNumber}.
  
  @return shard iterator
  @throws Exception