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https://issues.apache.org/jira/browse/AMQ-6203?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15302153#comment-15302153
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Timothy Bish commented on AMQ-6203:
-----------------------------------

Sounds right, the compaction is only done at times when the store isn't 
actively GC'ing old log files already, such times would be when the store is 
full or when the broker has been idle for awhile.  If things are running along 
fine, then there is not need for it to compact anything.  

> KahaDB: Allow rewrite of message acks in older logs which prevent cleanup
> -------------------------------------------------------------------------
>
>                 Key: AMQ-6203
>                 URL: https://issues.apache.org/jira/browse/AMQ-6203
>             Project: ActiveMQ
>          Issue Type: Improvement
>          Components: KahaDB
>    Affects Versions: 5.13.0, 5.13.1, 5.12.3, 5.13.2
>            Reporter: Timothy Bish
>            Assignee: Timothy Bish
>             Fix For: 5.14.0, 5.13.3
>
>
> There are cases where a chain of journal logs can grow due to acks for 
> messages in older logs needing to be kept so that on recovery proper state 
> can be restored and older messages not be resurrected.  
> In many cases just moving the acks from one log forward to a new log can free 
> an entire chain during subsequent GC cycles.  The 'compacted' ack log can be 
> written during the time between GC cycles without the index lock being held 
> meaning normal broker operations can continue.  



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