Quorum read
The technique of reading from (and writing to) enough replicas to guarantee you see the latest value, via the rule W + R > N. The heart of how leaderless databases (Dynamo, Cassandra) provide tunable consistency.
Mechanic: data lives on N replicas. A write is acknowledged by W nodes, a read queries R nodes. If W + R > N, the read and write sets must overlap in at least one node → that read is guaranteed to see the latest write. Trade-off via the choice of W and R: e.g. N=3, W=3, R=1 gives fast reads but slow/fragile writes; W=1, R=3 the opposite; W=2, R=2 is a balanced "quorum". The client can often choose the consistency level per operation (Cassandra: ONE, QUORUM, ALL). Win: fine-tune consistency vs latency vs availability without switching databases. Subtlety: it guarantees seeing a latest value, but not automatically linearizability (which requires read repair). Related to sloppy quorum and leaderless replication.