Eventual Consistency

Kind: model

Layer: Execution Core

Record: architecture:eventual-consistency

Severity: contextual

Scope: distributed system, data

Canonical: Ontology

A conceptual representation of a consistency guarantee in which replicas and projections converge once updates stop arriving.

Listed in Architecture principles, after Asynchronous Communication and before Saga Pattern.

Requires

• Idempotency
• Retry Pattern
• Reconciliation

Reinforces

• Availability
• Scalability

Enables

• Distributed Autonomy

In tension with

• User Expectations
• Strong Immediate Consistency
• Command Query Responsibility Segregation
• Command Query Responsibility Segregation (CQRS) / Eventual Consistency

Tensions

• Eventual Consistency / User Expectations
• Eventual Consistency / Strong Immediate Consistency

Violated by

• Global ACID Transaction

Refactored by

• Query Projection
• Reconciliation Job
• Saga Pattern

Severity

• contextual

Category

• Event / Messaging / Asynchronous Architecture

Reinforced by

• CRDTs
• CAP Theorem
• Idempotent Consumer

Linked from

• Separate, trade, or mitigate
• The ceiling moves by cost
• Causality / Ordering / Distributed Time
• Event / Messaging / Asynchronous Architecture
• Error Handling / Resilience
• Scalability / Performance / Optimization
• Transactions / State / Concurrency
• Event Messaging Async
• Quality Attributes
• Transactions / State / Concurrency
• Severity levels
• The resolutions