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https://issues.apache.org/jira/browse/OAK-3081?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14618469#comment-14618469
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Marcel Reutegger commented on OAK-3081:
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Remarks about the problem and the fix: the problem was that the head revision
could change between the the calls to doc.isCommitted(rev) and
SplitOperations.isGarbage(rev). The change was committed in the meantime and
the head revision is updated. This breaks an assumption in SplitOperations that
the head revision will reflect the same state about the commit as the previous
check with isCommitted(). The fix introduces a happens-before relation between
the head revision and the document to split and makes sure the head revision is
not newer than any uncommitted change observed in the document.
> SplitOperations may undo committed changes
> ------------------------------------------
>
> Key: OAK-3081
> URL: https://issues.apache.org/jira/browse/OAK-3081
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: core, mongomk
> Affects Versions: 1.0.10, 1.1.6, 1.2
> Reporter: Marcel Reutegger
> Assignee: Marcel Reutegger
> Priority: Blocker
> Fix For: 1.2.3, 1.3.3, 1.0.17
>
>
> There is a race condition when SplitOperations identifies garbage on a
> document. The feature was introduced with OAK-2421.
> The issue occurs if the following sequence of operations happens on a
> document:
> - The document is updated with e.g. _deleted.rX-0-1 = false within
> Commit.applyToDocumentStore()
> - Commit.createOrUpdateNode() perform the update and calls
> checkSplitCandidate(). The document becomes a split candidate, because it is
> over the threshold of 8kB
> - At the same time a background update is running and starts to look at the
> split candidates.
> - The background update looks at the document and calls
> SplitOperations.collectLocalChanges(). At this point _deleted.rX-0-1 = false
> is not committed and doc.isCommitted(rev) returns false
> - The commit proceeds, updates the commit root and sets the new head revision
> - The background update now calls SplitOperations.isGarbage(rX-0-1) and the
> method will return true!
> - The background update then removes _deleted.rX-0-1 = false together with
> the _commitRoot entry
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