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https://issues.apache.org/jira/browse/OAK-270?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13439356#comment-13439356
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Michael Dürig commented on OAK-270:
-----------------------------------
For the cluster case the general problem is the same as for locking (OAK-150):
in order to guarantee uniqueness we'd need some sort of global cluster
coordination. Event though we might not want to implement that right now, I
suggest we provide hooks for [external
coordinators|https://issues.apache.org/jira/browse/OAK-150?focusedCommentId=13401328&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13401328].
> Enforce uniqueness of jcr:uuid
> ------------------------------
>
> Key: OAK-270
> URL: https://issues.apache.org/jira/browse/OAK-270
> Project: Jackrabbit Oak
> Issue Type: Task
> Components: core, jcr
> Reporter: angela
>
> we had a quick discussion yesterday regarding enforcing uniqueness
> of jcr:uuid and how we are want/can assert that.
> in contrast to what was said yesterday in the meeting the jcr:uuid cannot
> be expected to be always a system generated random uuid. That's only true
> for those cases where a referenceable node is created using Node#addNode
> or Node#addMixin("mix:referenceable"). However, this is not the case when
> content is imported using Session#importXML or Workspace#importXML. in these
> situations the generation of the jcr:uuid is not governed by the system.
> exporting and re-importing items is very likely to produce uuid-collisions
> and we need to make sure we can verify and assert the uniqueness in these
> cases.
> from the current layout i think that a ValidatorProvider present during
> commit validation would be the right place for such an assertion. in order
> to verify the feasibility of that i approach i added a UUIDValidator to
> the oak/identifier package some days ago (validation not yet implemented).
> if we find out that this is not suitable or reliable we probably have to
> look for a solution closer to the mk.
> in any case (and irrespective of the final solution) we should make sure
> we understand the (potential) limitation of the uuid-uniqueness in a
> clustered environment, make sure our implementation gracefully deals with
> potential violations and have limitations documented.
> maybe it was also wise discussion under which circumstances such
> inconsistencies could be really harmful and where it might be acceptable.
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