Why do databases replicate data instead of just running on one powerful machine?
Replication solves three problems a single machine can't: fault tolerance (a copy survives if one machine fails), read scaling (multiple replicas can serve read traffic in parallel), and latency (data placed geographically closer to users reaches them faster). No single machine, however powerful, provides any of these — they require copies of the data existing in more than one place.
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Database Replication Explained: Single-Leader, Multi-Leader, and LeaderlessWhat replication lag actually breaks, and how single-leader, multi-leader, and leaderless models trade off consistency for availability.
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