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https://issues.apache.org/jira/browse/OAK-4826?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15522364#comment-15522364
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Marcel Reutegger commented on OAK-4826:
---------------------------------------
Depends upon OAK-4850.
> Auto removal of orphaned checkpoints
> ------------------------------------
>
> Key: OAK-4826
> URL: https://issues.apache.org/jira/browse/OAK-4826
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: core
> Reporter: Chetan Mehrotra
> Assignee: Marcel Reutegger
> Fix For: 1.6
>
>
> Currently if in a running system there are some orphaned checkpoint present
> then they prevent the revision gc (compaction for segment) from being
> effective.
> So far the practice has been to use {{oak-run checkpoints rm-unreferenced}}
> command to clean them up manually. This was set to manual as it was not
> possible to determine whether current checkpoint is in use or not.
> rm-unreferenced works with the basis that checkpoints are only made from
> AsyncIndexUpdate and hence can check if the checkpoint is in use by cross
> checking with {{:async}} state. Doing it in auto mode is risky as
> {{checkpoint}} api can be used by any module.
> With OAK-2314 we also record some metadata like {{creator}} and {{name}}.
> This can be used for auto cleanup. For example in some running system
> following checkpoints are listed
> {noformat}
> Mon Sep 19 18:02:09 EDT 2016 Sun Jun 16 18:02:09 EDT 2019
> r15744787d0a-1-1
>
> creator=AsyncIndexUpdate
> name=fulltext-async
> thread=sling-default-4070-Registered Service.653
>
> Mon Sep 19 18:02:09 EDT 2016 Sun Jun 16 18:02:09 EDT 2019
> r15744787d0a-0-1
>
> creator=AsyncIndexUpdate
> name=async
> thread=sling-default-4072-Registered Service.656
>
> Fri Aug 19 18:57:33 EDT 2016 Thu May 16 18:57:33 EDT 2019
> r156a50612e1-1-1
>
> creator=AsyncIndexUpdate
> name=async
> thread=sling-default-10-Registered Service.654
>
> Wed Aug 10 12:13:20 EDT 2016 Tue May 07 12:25:52 EDT 2019
> r156753ac38d-0-1
>
> creator=AsyncIndexUpdate
> name=async
> thread=sling-default-6041-Registered Service.1966
> {noformat}
> As can be seen that last 2 checkpoints are orphan and they would prevent
> revision gc. For auto mode we can use following heuristic
> # List all current checkpoints
> # Only keep the latest checkpoint for given {{creator}} and {{name}} combo.
> Other entries from same pair which are older i.e. creation time can be
> consider orphan and deleted
> This logic can be implemented
> {{org.apache.jackrabbit.oak.checkpoint.Checkpoints}} and can be invoked by
> Revision GC logic (both in DocumentNodeStore and SegmentNodeStore) to
> determine the base revision to keep
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