Glossary

Eventual Consistency

Eventual Consistency is a guarantee in distributed systems: if there are no new writes, all replicas will eventually converge to the same state. But at any given moment, different nodes may show different values.

Example

You liked a post on a social network. The counter changed immediately for you (local replica), but your friend in another region still sees the old count — and will see the updated one in a second or two when replication catches up.

Strong vs eventual consistency

Strong Consistency — after a write, all reads immediately see the new value. More expensive, higher latency
Eventual Consistency — cheaper and faster, but a brief window of stale reads

CRDT

Conflict-free Replicated Data Types — special data structures where conflicts between replicas are resolved automatically without coordination. For example, a distributed counter where each node independently increments its own value.