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https://issues.apache.org/jira/browse/OAK-7914?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Francesco Mari resolved OAK-7914.
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Resolution: Not A Problem
Fix Version/s: (was: 1.6.16)
> Cleanup updates the gc.log after a failed compaction
> ----------------------------------------------------
>
> Key: OAK-7914
> URL: https://issues.apache.org/jira/browse/OAK-7914
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: segment-tar
> Affects Versions: 1.6.15
> Reporter: Francesco Mari
> Assignee: Francesco Mari
> Priority: Critical
> Attachments: compaction.log
>
>
> The {{gc.log}} is always updated during the cleanup phase, regardless of the
> result of the compaction phase. This might cause a scenario similar to the
> following.
> - A repository of 100GB, of which 40GB is garbage, is compacted.
> - The estimation phase decides it's OK to compact.
> - Compaction produces a new head state, adding another 60GB.
> - Compaction fails, maybe because of too many concurrent commits.
> - Cleanup removes the 60GB generated during compaction.
> - Cleanup adds an entry to the {{gc.log}} recording the current size of the
> repository, 100GB.
> Now, let's imagine that compaction is run shortly after that. The amount of
> content added to the repository is negligible. For the sake of simplicity,
> let's say that the size of the repository hasn't changed. The following
> happens.
> - The repository is 100GB, of which 40GB is the same garbage that wasn't
> removed above.
> - The estimation phase decides it's not OK to compact, because the {{gc.log}}
> reports that the latest known size of the repository is 100GB, and there is
> not enough content to remove.
> This is in fact a bug, because there are 40GB worth of garbage in the
> repository, but estimation is not able to see that anymore. The solution
> seems to be not to update the {{gc.log}} if compaction fails. In other words,
> {{gc.log}} should contain the size of the *compacted* repository over time,
> and no more.
> Thanks to [~rma61...@adobe.com] for reporting it.
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