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https://issues.apache.org/jira/browse/CASSANDRA-5020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13509307#comment-13509307
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T Jake Luciani commented on CASSANDRA-5020:
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It would seem the better fix is to do better ref counting. There is a huge
benefit to having the data mapped since it lives off heap.
I've seen in mixed heavy read/write workloads this byte[] copy create a lot of
heap pressure.
> Time to switch back to byte[] internally?
> -----------------------------------------
>
> Key: CASSANDRA-5020
> URL: https://issues.apache.org/jira/browse/CASSANDRA-5020
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Jonathan Ellis
> Fix For: 1.3
>
>
> We switched to ByteBuffer for column names and values back in 0.7, which gave
> us a short term performance boost on mmap'd reads, but we gave that up when
> we switched to refcounted sstables in 1.0. (refcounting all the way up the
> read path would be too painful, so we copy into an on-heap buffer when
> reading from an sstable, then release the reference.)
> A HeapByteBuffer wastes a lot of memory compared to a byte[] (5 more ints, a
> long, and a boolean).
> The hard problem here is how to do the arena allocation we do on writes,
> which has been very successful in reducing STW CMS from heap fragmentation.
> ByteBuffer is a good fit there.
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