In a Shard MongoDB provide replication to replica set as pull mechanism, my question is if a write operation arrive at the primary with majority write concern then will it be waiting for all the operation in oplog to be replicated to all nodes or will just replicate this write operation to all nodes.
Since the oplog is replicated asynchronously the wait will only be for that particular write operation and not for the whole oplog.
Visit http://docs.mongodb.org/manual/core/distributed-write-operations/ for more details.