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From "Alex Parvulescu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OAK-4293) Refactor / rework compaction gain estimation
Date Tue, 09 Aug 2016 14:20:20 GMT

    [ https://issues.apache.org/jira/browse/OAK-4293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15413589#comment-15413589
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Alex Parvulescu commented on OAK-4293:
--------------------------------------

thanks for the ongoing feedback! pushed the reworked patch in with http://svn.apache.org/viewvc?rev=1755606&view=rev
This estimation mode can be currently enabled via the system property {{oak.segment.compaction.gcSizeDeltaEstimation}}
and/or via JMX but this will not be persisted. the default is still the old way of counting
garbage for now.

Still todo is the OSGi wiring for this setting, but I'm not sure this is the right issue to
track this enhancement. I'd like to make sure this works as desired, then provide bindings
to configure it.

> Refactor / rework compaction gain estimation 
> ---------------------------------------------
>
>                 Key: OAK-4293
>                 URL: https://issues.apache.org/jira/browse/OAK-4293
>             Project: Jackrabbit Oak
>          Issue Type: Task
>          Components: segment-tar
>            Reporter: Michael Dürig
>            Assignee: Alex Parvulescu
>              Labels: gc
>             Fix For: Segment Tar 0.0.10
>
>         Attachments: OAK-4293-v2.patch, size-estimation.patch
>
>
> I think we have to take another look at {{CompactionGainEstimate}} and see whether we
can up with a more efficient way to estimate the compaction gain. The current implementation
is expensive wrt. IO, CPU and cache coherence. If we want to keep an estimation step we need
IMO come up with a cheap way (at least 2 orders of magnitude cheaper than compaction). Otherwise
I would actually propose to remove the current estimation approach entirely 



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