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https://issues.apache.org/jira/browse/OAK-534?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Marcel Reutegger updated OAK-534:
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Attachment: OAK-534.patch
Attached patch introduces a OneLevelDiffCommand, which is used when MK.diff()
is called with depth = 0. It's a specialized version of DiffCommand, which
works with the commits collection to find out what the affected paths are in a
given revision range.
Please note that I also had to fix a test case to get the mongomk tests running
reliably on my Windows machine, but that's most likely unrelated to this issue.
> Inefficient NodeState comparison with MongoMK
> ---------------------------------------------
>
> Key: OAK-534
> URL: https://issues.apache.org/jira/browse/OAK-534
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: core, mongomk
> Affects Versions: 0.5
> Reporter: Marcel Reutegger
> Attachments: OAK-534.patch
>
>
> Oak on MongoMK currently results in complete tree traversal for any kind of
> modification. This is caused by the fact that MongoMK does not support the
> optional :hash system property. In this case
> KernelNodeState.compareAgainstBaseState() falls back to a generic
> implementation, which traverses the complete tree to find out if a subtree
> was modified.
> The NodeState comparison is triggered in almost all commit hook and validator
> implementations to find out what changed with the given commit.
> I see a number of options to solve this:
> 1) Add support for :hash system property in MongoMK
> 2) Use MK.diff() to find out if something was modified in a subtree
> 3) Use MK.getJournal() to find out if something was modified in a subtree
> Some initial thoughts on presented options to start the discussion (feel free
> to jump in and add more):
> Adding the :hash system property in MongoMK might not be that easy, because
> the implementation tries to avoid contention on the root node by not updating
> it with every commit. It only updates the nodes that actually changed. A
> straight forward implementation of :hash requires updating all ancestors of
> modified nodes.
> Option 2) seems to require additional work in MongoMK because the diff()
> implementation in MongoMK is using oak-mk DiffBuilder. The builder in turn
> will then call SimpleMongoNodeStore.compare(), which seems to use the same
> generic comparison implementation as the fallback in
> KernelNodeState.compareAgainstBaseState().
> AFAICS 3) might be a viable option with the recent support for branches in
> getJournal() (OAK-501). But I don't know how efficient this is implemented in
> MongoMK.
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