Got that -- sorry for the terminology error. I was thinking the same shard but in different data centers, so replicas of the same shard. Transactions within sin

Got that -- sorry for the terminology error. I was thinking the same shard but in different data centers, so replicas of the same shard. Transactions within single shard replica set are possible in v4.0. Transactions across multiple shards will be possible in v4.2. Reading the doc to try to see performance impact on transactions if multiple replicas of single shard.