Chetan Mehrotra created OAK-4826:
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Summary: 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
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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