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Enable Fault Tolerance and Failure Detection

Enable Fault Tolerance and Failure Detection

Understand how distributed key-value stores maintain availability and durability during node failures. Design sloppy quorum and hinted handoff mechanisms to handle temporary node outages. Apply Merkle trees for anti-entropy synchronization and gossip protocols for decentralized failure detection.

Handle temporary failures

Many distributed systems use a strict read/write quorum, where an operation must receive responses from a minimum number of replicas before it can proceed. If enough replicas are unavailable and the quorum cannot be satisfied, the operation fails, reducing availability. To maintain availability during such failures, the system can use a sloppy quorum.

In a sloppy quorum, the firstn\text{n}healthy nodes from the preference list handle read and write operations. These nodes may not be the designated owners in the consistent hash ring, but they ensure the request is processed.

Example: Consider a configuration where n = 3\text{n = 3}. If Node A\text{A} is unavailable during a write, the request is sent to the next healthy node, Node D\text{D} ...