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https://issues.apache.org/jira/browse/OAK-3864?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15094649#comment-15094649
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Michael Dürig commented on OAK-3864:
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Thinking a bit more about this I came to the conclusion that 2. is not
feasible: it would put constraints on the order in which segment buffer writers
could flush. This would either re-introduce blocking (which to remove was a
purpose of OAK-1828) or require a much deeper refactoring effectively
redesigning the way segments are written and flushed.
1. should be feasible. Exploiting the fact that forward references are rare and
only span a few segments it should even be possible to fix cleanup without
having to resort to a full fledged mark and sweep. The idea would be to do a
first forward pass over the segments collecting the forward references. The
following backward pass would then use those to augment the reference set
passed along.
> Filestore cleanup removes referenced segments
> ---------------------------------------------
>
> Key: OAK-3864
> URL: https://issues.apache.org/jira/browse/OAK-3864
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: segmentmk
> Reporter: Michael Dürig
> Assignee: Michael Dürig
> Priority: Blocker
> Labels: regression
> Fix For: 1.3.14
>
>
> In some situations {{FileStore.cleanup()}} may remove segments that are still
> referenced, subsequently causing a {{SNFE}}.
> This is a regression introduced with OAK-1828.
> {{FileStore.cleanup()}} relies on the ordering of the segments in the tar
> files: later segments only reference earlier segments. As we have seen in
> other places this assumption does not hold any more (e.g. OAK-3794, OAK-3793)
> since OAK-1828.
> {{cleanup}} traverses the segments backwards maintaining a list of
> referenced ids. When a segment is not in that list, it is removed. However,
> this approach does not work with forward references as those are only seen
> later when the segment has been removed already.
> cc [~alex.parvulescu], [~frm]
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