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https://issues.apache.org/jira/browse/OAK-6507?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16116207#comment-16116207
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Michael Dürig commented on OAK-6507:
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Looking at the logic in {{Reclaimers.newOldReclaimer}} I tried to come up with
a simpler approach (which involves changing the semantics of {{GCGeneration}}:
basically a segments is reclaimable iff it is old and not in the same
compaction tail as the segment of the current head state. A segment is old iff
was created by a gc (full or tail) more than the number of retained generations
in the past. A segment is in the same compaction tail as another one iff both
share the same full generation. Encoding this definition and working it
backwards results in the following fields we need to record in the segments:
the gc generation (incremented on each gc run, full or tail). The full
generation (incremented only on full gc runs) and an compaction flag indicating
whether a segment has been written by a compaction operation (either full or
tail).
> Cleanup incorrectly removes base state created by full compaction
> -----------------------------------------------------------------
>
> Key: OAK-6507
> URL: https://issues.apache.org/jira/browse/OAK-6507
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: segment-tar
> Reporter: Francesco Mari
> Assignee: Francesco Mari
> Fix For: 1.8, 1.7.6
>
>
> The predicate used to mark segments for cleanup marks segments written by
> full compactions. These segments are needed to reconstruct the full state of
> the repository, together with the state built by tail compactions.
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