How does MongoDB ensure data consistency?

MongoDB ensures data consistency by using write concern replication and sharding functionality.

1. Write Concern Replication: MongoDB utilizes replica sets to achieve data replication and redundancy storage. A replica set consists of a primary node and multiple secondary nodes. When a client writes data, the primary node replicates the write operation to all secondary nodes to ensure data consistency. Clients can set write concern to specify conditions for the success of the write operation, such as requiring the write operation to be replicated to multiple secondary nodes to be considered successful.
2. Sharding: MongoDB has the ability to distribute data across multiple physical servers to achieve horizontal scaling. Sharding ensures data consistency by dividing data according to a specified shard key and storing data with the same shard key on the same shard. This ensures that data with the same shard key is queried on the same shard, thereby maintaining data consistency.

In conclusion, MongoDB uses replica sets and sharding to ensure data consistency through replication of write operations and distributed data storage.