[jira] [Created] (OAK-4826) Auto removal of orphaned checkpoints

["Chetan Mehrotra (JIRA)" <ji...@apache.org>]

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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