Conflict-Free Replicated Data Type
A data structure whose replicas can be edited independently and always converge without coordination.
A conflict-free replicated data type is a data structure designed so that independent replicas, edited concurrently and merged in any order, always converge to the same value — with no central authority and no coordination.
The property that makes this work is that merging is commutative, associative, and idempotent: order and duplication do not matter. Operations can therefore arrive out of order, arrive twice, or arrive after an arbitrary delay, and the result is the same. This is what allows offline editing to be a first-class capability rather than a special mode.
The trade is that convergence is guaranteed and intent is not. Two people editing the same word produce a deterministic result that neither may have wanted; the structure guarantees agreement, not satisfaction. Text CRDTs go to considerable lengths — identifiers per character, tombstones for deletions — to make the outcome feel reasonable, at the cost of metadata that grows with edit history.
Mature libraries make them practical for real applications: a shared document type, awareness of who is present, and pluggable transports so the same document can synchronize over a server, over WebRTC, or through a local database. That last property is the interesting one architecturally — it makes a collaborative application possible with no server that anyone has to run.
See also7
Eventual Consistency
A guarantee that replicas converge given no further updates, without guaranteeing when.
Networks & Distribution22 connections
Peer-to-Peer
An architecture where participants communicate directly rather than through a central server.
Networks & Distribution13 connections
WebRTC
The browser standard for direct peer connections carrying audio, video, and arbitrary data.
Networks & Distribution14 connections
Idempotence
The property that performing an operation twice has the same effect as performing it once.
Systems & Tooling34 connections
Signaling Server
The small coordination service peers use to find each other before connecting directly.
Networks & Distribution10 connections
Soft Delete
Marking a record as deleted instead of removing it, which makes deletion reversible and auditable but leaks complexity into every query.
Data & Content11 connections
Universally Unique Identifier
A 128-bit identifier that any machine can generate without coordination and still be practically certain no one else will produce the same one.
Data & Content10 connections
Related1
Nearby in the graph rather than deliberately chosen. Looser, sometimes surprising.
Linked from11
- CAP TheoremData & Content
When a network splits a distributed system, it can stay consistent or stay available, but a proven theorem says not both.
- Eventual ConsistencyNetworks & Distribution
A guarantee that replicas converge given no further updates, without guaranteeing when.
- IdempotenceSystems & Tooling
The property that performing an operation twice has the same effect as performing it once.
- Network PartitionNetworks & Distribution
A network failure that splits a cluster into groups that can't reach each other but keep running, and the split brain that follows when each side thinks it is in charge.
- Peer-to-PeerNetworks & Distribution
An architecture where participants communicate directly rather than through a central server.
- Signaling ServerNetworks & Distribution
The small coordination service peers use to find each other before connecting directly.
- Soft DeleteData & Content
Marking a record as deleted instead of removing it, which makes deletion reversible and auditable but leaks complexity into every query.
- UndoDesign & Interface
Letting people reverse what they just did, which makes interfaces safe to explore and usually beats asking "are you sure?" before every action.
- Universally Unique IdentifierData & Content
A 128-bit identifier that any machine can generate without coordination and still be practically certain no one else will produce the same one.
- Web StorageWeb Platform
The browser's built-in ways to keep data on the user's device, from the simple string store localStorage to the transactional database IndexedDB, and their limits on size, persistence and security.
- WebRTCNetworks & Distribution
The browser standard for direct peer connections carrying audio, video, and arbitrary data.