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https://issues.apache.org/jira/browse/OAK-638?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13581218#comment-13581218
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Marcel Reutegger commented on OAK-638:
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bq. initially live only in local memory
This sounds like a reasonable optimization. Though, my understanding so far was
that commits to a branch are actually persisted. After all, we use the same
method 'commit' to stage those changes in the branch and all existing MK
implementations actually perform IO.
bq. the MK implementation has much better information about the relative costs
of different storage accesses and can thus make better decisions about how to
best handle branches
This pretty much means we should push down handling of the transient space to
the MK implementation. I don't think the MK was designed with this in mind. My
understanding so far is that we handle transient operations in oak-jcr (to a
certain amount: RootImpl#PURGE_LIMIT) and _persist_ those changes to a branch
once over the limit.
On the other hand I agree with you that the KernelNodeStore implementation is
in a rather unenviable position. It doesn't know what happens in oak-jcr nor
can it perform low level optimizations that belong into the MK.
> Avoid branch/merge for small commits
> ------------------------------------
>
> Key: OAK-638
> URL: https://issues.apache.org/jira/browse/OAK-638
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: core
> Reporter: Marcel Reutegger
> Priority: Minor
>
> The branch/merge features on the MicroKernel were initially introduced to
> stage changes of large commits. Currently oak-core creates a branch even for
> small changes like updating a property. I think this introduces quite some
> overhead for scenarios with highly concurrent updates. E.g. think of a
> twitter like application or a forum with comments. Well, basically user
> generated content. These update tend to be rather small (couple of nodes) but
> frequent and concurrent.
> Right now oak-core always does:
> - MK.branch()
> - MK.commit() to branch
> - MK.merge()
> For small commits, it ideally should do:
> - MK.commit() to trunk
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