What do read consistency and write consistency indicate in Cassandra?

Read consistency and write consistency in Cassandra refer to the specific levels of consistency that the database maintains for read and write operations. This concept is crucial because Cassandra is designed to provide a balance between availability, performance, and consistency, especially in distributed systems.

Read consistency defines how many replicas of data need to respond to a read request for it to be considered successful. For instance, if a read operation is set to a consistency level of "QUORUM," it requires a majority of replicas to agree on the value before returning a response. This approach ensures that the most recent and accurate data is retrieved, which is particularly important when considering scenarios with concurrent updates.

Similarly, write consistency indicates how many replicas must acknowledge a write operation before it is considered successful. For example, a consistency level of "ALL" means that all replicas must confirm the write before it is finalized. This setting directly affects how quickly and reliably data is written to the database.

By understanding read and write consistency levels, users can configure their applications to meet specific needs for data accuracy and availability. This flexibility allows developers to optimize performance based on their specific application requirements, crucial for creating resilient distributed systems.