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Intermediate 1 minute
Strong vs Eventual Consistency
Consistency describes what value a read is allowed to observe after writes happen. Strong consistency makes a successful read reflect the latest accepted write, which is easier for users to reason about but can cost latency or availability. Eventual consistency allows temporary differences between replicas in exchange for speed and resilience, as long as copies converge when updates stop.
Key idea
Strong favors an immediate, shared view; eventual favors availability with a convergence window.
See it in one picture
Follow the arrowsWrite
Replica A
Replica B
Read
Do both copies agree right away?
Real-world example
A bank balance generally needs strong guarantees. A social media like count can tolerate a few seconds of disagreement between regions if the experience remains responsive.
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