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Dotted Version Vector Sets

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

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

Usage examples

  • Creating a new version
DVVSet dvvSet = new DVVSet();
Clock dot = dvvSet.create(dvvSet.newDvv("1611600920427"), "user_id_1");
  • Incrementing version
List context = dvvSet.join(dot);
Clock newDot = dvvSet.update(dvvSet.newWithHistory(context, "1616682865530"), dot, "user_id_2");
List mergedHistory = dvvSet.sync(new Clock(dot.asList(), newDot.asList()));
  • Detecting conflicts

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

List values = dvvSet.values(mergedHistory);
if (values.size() > 1) {
    System.out.println("CONFLICT");
} else {
    System.out.println("OK");
}

Example

  1. User 1 uploads file to the server, specifying version vector:
DVVSet dvvSet = new DVVSet();
Clock dot = dvvSet.create(dvvSet.newDvv("1611600920427"), "user_id_1");
  1. Server checks version on a subject of conflict. Then it stores file with version information and provides it to User 2.
List mergedHistory = dvvSet.sync(new Clock(existingVersion, uploadedVersion));
List values = dvvSet.values(mergedHistory);
if (values.size() > 1) {
    // return 409 Conflict
} else {
    // return 200 OK
}
  1. User 2 downloads file, edits it and increments its version, before uploading back to server.
List context = dvvSet.join(dot);
Clock newDot = dvvSet.update(dvvSet.newWithHistory(context, "1616682865530"), dot, "user_id_2");
dvvSet.sync(new Clock(dot.asList(), newDot.asList()));