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https://issues.apache.org/jira/browse/OAK-3612?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15002086#comment-15002086
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Francesco Mari commented on OAK-3612:
-------------------------------------
[~alex.parvulescu], the record cache in the {{SegmentWriter}} is actually
cleaned up
[here|https://github.com/apache/jackrabbit-oak/blob/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/file/FileStore.java#L1434]
on successful compaction.
Anyway, I can confirm that in the context of the Cold Standby it is important
to have this change in place. I could convince myself by doing the following:
1. Generate garbage on the primary.
2. Take heap dump #1 on the standby.
3. Run compaction on the primary.
4. Take heap dump #2 on the standby.
5. Cleanup the standby using the JMX bean.
6. Take heap dump #3 on the standby.
I use the heap dump #1 to retrieve the {{SegmentId}} of the current root state,
and search for that same {{SegmentId}} in the heap dump #2. This allows me to
find who references the old root state before cleanup is called on the standby.
In my tests, I usually have the following references:
- A reference from {{CacheLIRS}}.
- A weak reference from {{SegmentTracker}}. Being a weak reference, this can be
ignored for the purpose of our conversation.
- A reference from {{SegmentWriter}}.
On the standby, the cleanup phase is called without executing the compaction
phase first. The {{FileStore#cleanup}} method takes care of clearing
{{CacheLIRS}} (through {{SegmentTracker#clearCache}}). The only missing
(non-weak) reference, that nobody takes care of, is the one from
{{SegmentWriter}}. If you reproduce the steps above, you will see from the heap
dump #3 that the only reference to the old {{SegmentId}} is precisely the one
from {{SegmentWriter}}.
> The string/template cache of the SegmentWriter should be cleared before
> cleanup
> -------------------------------------------------------------------------------
>
> Key: OAK-3612
> URL: https://issues.apache.org/jira/browse/OAK-3612
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: segmentmk
> Reporter: Francesco Mari
> Fix For: 1.4
>
> Attachments: OAK-3612-01.patch
>
>
> The string/template cache of the SegmentWriter
> (org.apache.jackrabbit.oak.plugins.segment.SegmentWriter#records) is not
> cleared before the cleanup phase. This might maintain in-memory references to
> segments, thus preventing them to be cleaned up.
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