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The most important thing is to display the content to every user and allow them to update the intent if the CRDT rules are incorrect for that use case. Therefor

The most important thing is to display the content to every user and allow them to update the intent if the CRDT rules are incorrect for that use case. Therefore the most important thing is not the fact that it's conflict-free, it's that it builds exactly the same document for all users no matter what order the operations are applied in (if it's operations based, rather than merge based).

jorangreef 10y ago
"the most important thing is not the fact that it's conflict-free" CRDT is actually an acronym for both "Conflict-free replicated data type" and "Commutative replicated data type". Both properties are provided by a CRDT by definition. Both properties are equally important. "(if it's operations based, rather than merge based)" CRDTs are commutative by definition irrespective of whether they are operation based or state based.
- skybrian 10y ago
  As I understand it, sometimes they do this via techniques roughly similar to inserting change markers (that is, remember both versions). The change may technically be "conflict free" according to the algorithm's definition, but from the user's point of view, the merge has not been completed until you pick which version to keep. Informally, each place we need to manually do a merge can be considered an unresolved conflict according to an alternate definition of "conflict".
  - jorangreef 10y ago
    If you need to pick a version, then it's not a CRDT. Normally, you would use the right CRDT to fit the problem space, provided the problem space can be modeled using commutative operations. CRDTs require the problem space to be defined in terms of commutative operations. That's just a requirement of the data structure, just like binary search requires a sorted list. If that requirement is met, then there would be no conflicts and no merges by design. That's the beauty of CRDTs. They are perfect for multi-master distributed settings. You wouldn't use a CRDT to store the raw contents of an Excel document or a Javascript file, since those file formats were not designed to be modeled using commutative operations. I think that's the use case you have in mind? For that you would need manual merges, regardless of the data structure or binary string you use to represent the document.

jorangreef 10y ago

"the most important thing is not the fact that it's conflict-free" CRDT is actually an acronym for both "Conflict-free replicated data type" and "Commutative replicated data type". Both properties are provided by a CRDT by definition. Both properties are equally important. "(if it's operations based, rather than merge based)" CRDTs are commutative by definition irrespective of whether they are operation based or state based.

skybrian 10y ago
As I understand it, sometimes they do this via techniques roughly similar to inserting change markers (that is, remember both versions). The change may technically be "conflict free" according to the algorithm's definition, but from the user's point of view, the merge has not been completed until you pick which version to keep. Informally, each place we need to manually do a merge can be considered an unresolved conflict according to an alternate definition of "conflict".
- jorangreef 10y ago
  If you need to pick a version, then it's not a CRDT. Normally, you would use the right CRDT to fit the problem space, provided the problem space can be modeled using commutative operations. CRDTs require the problem space to be defined in terms of commutative operations. That's just a requirement of the data structure, just like binary search requires a sorted list. If that requirement is met, then there would be no conflicts and no merges by design. That's the beauty of CRDTs. They are perfect for multi-master distributed settings. You wouldn't use a CRDT to store the raw contents of an Excel document or a Javascript file, since those file formats were not designed to be modeled using commutative operations. I think that's the use case you have in mind? For that you would need manual merges, regardless of the data structure or binary string you use to represent the document.