Consistency
Eventual Consistency
IntermediateHow eventual consistency models propagate updates across nodes, how convergence windows create read anomalies, how conflict resolution works, and when strong consistency is required instead.
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Consistent State: All Nodes Agree
In a consistent state, all replicas hold the same data. A read to any node returns the same value. Under eventual consistency, this is the steady state after all writes have propagated. Systems like Cassandra and DynamoDB work toward this state: but make no guarantee about when convergence will occur after a write.
Node A
consistent
user:42 → plan=free
Node B
consistent
user:42 → plan=free
Node C
consistent
user:42 → plan=free
All three nodes consistent: reads from any node return plan=free
Key Takeaways
- →Convergence is the eventual goal: but it is not instantaneous
- →Under no load and no failures, eventual consistency and strong consistency look identical
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