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https://issues.apache.org/jira/browse/OAK-6220?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16011886#comment-16011886
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Marcel Reutegger commented on OAK-6220:
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The DocumentNodeStore implementation does not support multiple builders off a
branched node state. See also OAK-1838. This is most likely the reason why some
tests fail.
I would rather solve this by composition. Take any NodeStore implementation
(unaware of CoW) and layer a CoW NodeStore implementation on top of it. It
would be yet another option in the nstab proposal (e.g. volatile). The CoW
NodeStore could be based on a checkpoint which is created on startup and
released on shutdown.
I think the existing MemoryNodeStore already supports this to some degree. It's
in-memory only and does not expose the checkpoints of an underlying store, but
it can be based on any NodeState.
> Copy on write node store implementation
> ---------------------------------------
>
> Key: OAK-6220
> URL: https://issues.apache.org/jira/browse/OAK-6220
> Project: Jackrabbit Oak
> Issue Type: New Feature
> Components: core
> Reporter: Tomek Rękawek
> Fix For: 1.8
>
> Attachments: OAK-6220-2.patch, OAK-6220.patch
>
>
> The copy-on-write (COW) node store implementation would allow to temporarily
> switch the repository into the "testing" mode, in which all the changes are
> saved in a reversible way. After switching back to the "production" mode, the
> test changes should be dropped.
> This should include checkpoints as well.
> Because the SegmentNodeStore supports COW natively, we may simply copy the /
> tree to some user-provided path and use it as a new root. For the
> DocumentNodeStore we'll need something more complex.
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