# CRDTs

> A mechanism that stores replicated state in data types whose merge is commutative, so replicas converge without coordination.

Record: `architecture:crdts`
Kind: mechanism
Layer: [Causality Core](https://banes-lab.com/records/layer/causality-core.md)
Severity: contextual
Scope: distributed state, replication, convergence
Aliases: Conflict-Free Replicated Data Types
Canonical: https://banes-lab.com/ontology#architecture-crdts

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Hybrid Logical Clocks](https://banes-lab.com/records/architecture/hybrid-logical-clocks.md) and before [Total-Order Broadcast](https://banes-lab.com/records/architecture/total-order-broadcast.md).

## Repair

- Refactored by: Model State as a CRDT
- Detected by: lost updates under concurrent replication
- Violated by: concurrent replica edits silently overwriting each other
- Measured by: merge-conflict data-loss rate
- Enforced by: replication design review

## Requires

- [Commutative Merge](https://banes-lab.com/records/lexicon/commutative-merge.md)

## Reinforces

- [Eventual Consistency](https://banes-lab.com/records/architecture/eventual-consistency.md)
- [Causal Consistency](https://banes-lab.com/records/architecture/causal-consistency.md)

## Enables

- [Conflict-Free Replica Convergence](https://banes-lab.com/records/lexicon/conflict-free-replica-convergence.md)

## In tension with

- [Metadata Overhead](https://banes-lab.com/records/lexicon/metadata-overhead.md)
- [Last-Write-Wins Overwrite](https://banes-lab.com/records/lexicon/last-write-wins-overwrite.md)

## Tensions

- [CRDTs / Metadata Overhead](https://banes-lab.com/records/tension/crdts-metadata-overhead.md)
- [CRDTs / Last-Write-Wins Overwrite](https://banes-lab.com/records/tension/crdts-last-write-wins-overwrite.md)

## Severity

- [contextual](https://banes-lab.com/records/vocabulary/severity-contextual.md)

## Category

- [Causality / Ordering / Distributed Time](https://banes-lab.com/records/architecture-category/causality-ordering-distributed-time.md)

## Linked from

- [Causality / Ordering / Distributed Time](https://banes-lab.com/ontology/principles/architecture-category-causality-ordering-distributed-time.md)
- [Event / Messaging / Asynchronous Architecture](https://banes-lab.com/ontology/principles/architecture-category-event-messaging-asynchronous-architecture.md)
- [Causality / Ordering / Distributed Time](https://banes-lab.com/ontology/lexicon/lexicon-category-causality-ordering-distributed-time.md)
- [Severity levels](https://banes-lab.com/ontology/schema/the-vocabulary-severity.md)
- [The resolutions](https://banes-lab.com/ontology/schema/the-resolutions.md)