Dotted Version Vector Sets

This is an implementation of the Erlang's DVV on JavaScript.

It is used in distributed systems, where UTC timestamp is unreliable value for object's version control.

Usage examples

• Creating a new version

const dvv = new Dvv();
const modified_utc = Date.now().toString(); // timestamp value is used for example only. It can be anything.
const dot = dvv.create(dvv.new_dvv(modified_utc), 'user_id_1');

• Incrementing version

const context = dvv.join(dot);
const modified_utc2 = Date.now().toString();
const new_dot = dvv.update(dvv.new_with_history(context, modified_utc2), dot, 'user_id_2');
dvv.sync([dot, new_dot]);

• Detecting conflicts

Conflict is situation when two branches of the history exist. It could happen when someone updates old version ( casual history ).

const merged_history = dvv.sync([OldVersion, NewVersion]);
const values = dvv.values(merged_history);
values.length > 1
	? console.log('Conflict detected')
	: console.log('Ok');

Example

1. User 1 uploads file to the server, specifying version vector:

const dvv = new Dvv();
const modified_utc = Date.now().toString();
const dot = dvv.create(dvv.new_dvv(modified_utc), 'user_id_1');

2. Server checks version on a subject of conflict. Then it stores file with version information and provides it to User 2.

const merged_history = dvv.sync([ExistingVersion, UploadedVersion]);
const values = dvv.values(merged_history);
values.length > 1
	? console.log('409 Conflict detected')
	: console.log('200 OK') // Casual history is linear

3. User 2 downloads file, edits it and increments its version, before uploading back to server.

const context = dvv.join(dot); // dot is a downloaded version
const modified_utc = Date.now().toString();
const new_dot = dvv.update(dvv.new_with_history(context, modified_utc), dot, 'user_id_2');
dvv.sync([dot, new_dot]);