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https://issues.apache.org/jira/browse/OAK-6888?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16240016#comment-16240016
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Francesco Mari commented on OAK-6888:
-------------------------------------
The forceful implementation of {{flush}} guarantees better persistence (and
thus, in the case of the standby, visibility) properties than the previous one.
As such, it can help to implement more complex scenarios with higher
confidence. Can you outline a scenario where a more flexible flush policy could
be needed?
> Flushing the FileStore might return before data is persisted
> ------------------------------------------------------------
>
> Key: OAK-6888
> URL: https://issues.apache.org/jira/browse/OAK-6888
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: segment-tar
> Reporter: Francesco Mari
> Assignee: Francesco Mari
> Fix For: 1.8, 1.7.11
>
> Attachments: failure.txt
>
>
> The implementation of {{FileStore#flush}} might return before all the
> expected data is persisted on disk.
> The root cause of this behaviour is the implementation of
> {{TarRevisions#flush}}, which is too lenient when acquiring the lock for the
> journal file. If a background flush operation is in progress and a user calls
> {{FileStore#flush}}, that method will immediately return because the lock of
> the journal file is already owned by the background flush operation. The
> caller doesn't have the guarantee that everything committed before
> {{FileStore#flush}} is persisted to disk when the method returns.
> A fix for this problem might be to create an additional implementation of
> flush. The current implementation, needed for the background flush thread,
> will not be exposed to the users of {{FileStore}}. The new implementation of
> {{TarRevisions#flush}} should have stricter semantics and always guarantee
> that the persisted head contains everything visible to the user of
> {{FileStore}} before the flush operation was started.
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