Nosql Questions Long
In NoSQL databases, different consistency models are used to define how data is synchronized and distributed across multiple nodes in a distributed system. These models determine the level of consistency and availability that can be achieved in the database. Here are some of the commonly used consistency models in NoSQL databases:
1. Strong Consistency: In this model, the database guarantees that all reads will return the most recent write or an error. It ensures that all replicas of the data are updated before a read operation is performed. Strong consistency provides a linearizable and sequential ordering of operations, but it may impact system performance and availability.
2. Eventual Consistency: This model allows replicas to be inconsistent temporarily but guarantees that eventually, all replicas will converge to the same state. It allows for high availability and low latency by allowing concurrent updates to different replicas. Eventual consistency is suitable for applications where immediate consistency is not critical, such as social media feeds or recommendation systems.
3. Read-your-writes Consistency: This model guarantees that a read operation will always return the most recent write performed by the same client. It ensures that a client will never see stale data that it has previously written. Read-your-writes consistency is commonly used in systems where strong consistency is not required but maintaining session consistency is important.
4. Monotonic Reads Consistency: This model guarantees that if a client has seen a particular version of data, it will not see older versions in subsequent reads. It ensures that the data seen by a client is always moving forward in time. Monotonic reads consistency is useful in scenarios where clients need to observe a consistent view of the data without requiring strong consistency.
5. Monotonic Writes Consistency: This model guarantees that writes from a client are always seen in the same order by all subsequent reads from that client. It ensures that writes are not reordered or lost during replication. Monotonic writes consistency is useful in scenarios where maintaining the order of writes is important, such as maintaining a log or audit trail.
6. Causal Consistency: This model guarantees that if there is a causal relationship between two operations, the order of their execution will be preserved across all replicas. It ensures that operations that are causally related are seen in the same order by all clients. Causal consistency is important in systems where the order of operations matters, such as distributed transactions or collaborative editing.
It's worth noting that different NoSQL databases may implement different consistency models or provide configurable options to choose the desired level of consistency based on the specific requirements of the application.