[jira] [Commented] (CASSANDRA-6544) Reduce GC activity during compaction

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-6544?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13864656#comment-13864656 ] 

Jonathan Ellis commented on CASSANDRA-6544:
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So just a Native ByteBuffer to hold the merged cell name/values, that we throw away when the compaction is done?

> Reduce GC activity during compaction
> ------------------------------------
>
>                 Key: CASSANDRA-6544
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6544
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Vijay
>            Assignee: Vijay
>             Fix For: 2.1
>
>
> We are noticing increase in P99 while the compactions are running at full stream. Most of it is because of the increased GC activity (followed by full GC).
> The obvious solution/work around is to throttle the compactions, but with SSD's we can get more disk bandwidth for reads and compactions.
> It will be nice to move the compaction object allocations off heap. First thing to do might be create a Offheap Slab allocator with the size as the compaction in memory size and recycle it. 
> Also we might want to make it configurable so folks can disable it when they don't have off-heap memory to reserve.



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