RTBS Rypin – Rypińskie Towarzystwo Budownictwa Społecznego

When Alice adds a message optimistically to her replica, she can simulate almost everything in the final result except the id .

The id is an important part of the message identity as it assigns uniqueness to each message in the replica collection. The id is also an important part of the view creation logic as it is used as the key in the React render function that maps an array of messages to JSX.

Resolving conflict in the two different id versions should be avoided. We are venturing into dangerous territories when the clients are in the business of reasoning about the provenance of data in its local copy. This could introduce a leaky abstraction problem wherein the client needs to know the implementation details of the server (e.g., how an id is picked), which can cause the system to be fragile and error-prone.

There are two ways to avoid performing conflict resolution on the id . Choosing which approach to pursue depends on the constraints and non-functional requirements imposed on the project. In particular, this is a tradeoff between technical complexity on the back-end vs front-end.

Conflict Avoidance (server-side)

A server-generated id for message was a constraint for the offline-first chat app project. The chat app was originally built to not be usable while offline. Users could not create new messages to be queued for sending while they are offline.

If we were building an offline-first chat app from scratch, we could have totally avoided the two different versions of id by making the real id client-generated.

• For the new message, the client generates a UUID then send that to the server.
• The server implements format check, duplicate check, and date check on the UUID. If any of these checks fail, reject the message send request.

This approach does not alleviate the clients from tracking what’s real and what’s optimistic in their replicas but it significantly simplifies the replica implementation as it can be implemented as a growth-only set. Czytaj więcej →