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https://issues.apache.org/jira/browse/CASSANDRA-6689?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13923201#comment-13923201
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Benedict commented on CASSANDRA-6689:
-------------------------------------
The smallest direct byte buffer from Netty is on the order of 64-bytes minimum,
whereas we manage 24-bytes; plus for maintaining the allocation list we then
need to have a separate list, rather than chaining the allocations, so at least
another 4-bytes overhead (more, but in best case it tends to 4).
[https://github.com/netty/netty/blob/master/buffer/src/main/java/io/netty/buffer/AbstractByteBuf.java]
[https://github.com/netty/netty/blob/master/buffer/src/main/java/io/netty/buffer/UnpooledUnsafeDirectByteBuf.java]
> Partially Off Heap Memtables
> ----------------------------
>
> Key: CASSANDRA-6689
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6689
> Project: Cassandra
> Issue Type: New Feature
> Components: Core
> Reporter: Benedict
> Assignee: Benedict
> Fix For: 2.1 beta2
>
> Attachments: CASSANDRA-6689-small-changes.patch
>
>
> Move the contents of ByteBuffers off-heap for records written to a memtable.
> (See comments for details)
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