What is Cassandra's consistency vs availability trade-off with tunable consistency?

Cassandra's tunable consistency allows per-query configuration of the consistency/availability trade-off. The key formula: writes + reads > replication factor = strong consistency. With RF=3: ONE + QUORUM = 1 + 2 = 3 = RF — NOT strongly consistent (reads might miss recent writes). QUORUM + QUORUM = 2 + 2 = 4 > 3 — strongly consistent. ALL + ONE = 3 + 1 = 4 > 3 — strongly consistent. Practical configurations: Maximum availability, eventual consistency: write ONE, read ONE. Balance (recommended for most apps): write LOCAL_QUORUM, read LOCAL_QUORUM. Strong consistency within a DC without cross-DC latency. Maximum consistency: write ALL, read ONE. Any node has the latest write. Availability with tunable read freshness: write ONE, read QUORUM. Writes are fast; reads are more consistent. The beauty of tunable consistency: you can use different levels for different operations — QUORUM for financial data, ONE for analytics/metrics.