Skip to content

Eventual Consistency

One-Liner

The system converges to a consistent state over time.

What It Is

A consistency model where updates propagate asynchronously and temporary divergence is allowed.

Why It Exists

Strong consistency is expensive or unnecessary for many systems.

How It Works

Writes are accepted independently and reconciled later.

Tradeoffs

Pros

Higher availability
Better scalability

Cons

Temporary inconsistency
More complex application logic

Failure Modes

Conflicting writes
User-visible anomalies

Interview Traps

Using eventual consistency without defining acceptable inconsistency

Real-World Usage

Social feeds, metrics systems, caches.

Anti-Patterns

Applying to financial or critical correctness domains

CAP theorem
Conflict resolution