What is a Hinted Handoff in Cassandra?

Hinted Handoff in Cassandra refers to a mechanism that allows for consistency in data writes when a node is temporarily unavailable. When a write request is received, if the intended node for the write is down or unreachable, another node within the cluster can take on the responsibility of holding the write request. This temporary storage of the write is known as a "hint," which informs the unavailable node about what it missed when it comes back online.

Once the unavailable node is restored and reconnects to the cluster, the hints can be replayed, ensuring that it receives the missed write information. This process helps maintain data consistency and availability by preventing write operations from being lost due to transient outages. Therefore, this mechanism is critical for ensuring fault tolerance and seamless recovery in a distributed system like Cassandra, where node availability can vary.

The other options do not accurately capture the essence of Hinted Handoff. While optimizing read requests, directly handing off queries, or inter-node communication are all important aspects of Cassandra's functionality, they do not pertain specifically to the concept of Hinted Handoff, which focuses primarily on ensuring that writes can still be captured and delivered even if the intended node is not currently available.