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https://issues.apache.org/jira/browse/CASSANDRA-6694?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13983709#comment-13983709
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Pavel Yaskevich edited comment on CASSANDRA-6694 at 4/28/14 11:29 PM:
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Here is a [new branch|https://github.com/xedin/cassandra/compare/6694-final]
with all of the changes from 6694-reorg2 squashed and added a couple of commits
to cleanup and remove secondary index getAllocator which is unnecessary right
now. I was about to push similar refactoring for memtable pools to my branch,
which made review much faster :)
I'm +1 on combination of the squashed changes and cleanup which is in my
branch, still not sure about CellName implementation in AbstractNativeCell tho,
that is not my realm, so it would be nice if [~slebresne] (or somebody as close
to that code, if anybody) could take a look...
was (Author: xedin):
Here is a [new branch|https://github.com/xedin/cassandra/compare/6694-final]
with all of the changes from 6694-reorg2 squashed and added a couple of commits
to cleanup and remove secondary index getAllocator which is unnecessary right
now. I was about to push similar refactoring for memtable pools to my branch,
which made review much faster :)
I'm +1 on combination of the squashed changes and cleanup which is in my
branch, still not sure about CellName implementation in AbstractNativeCell tho,
that is not my realm, so it would be nice if Sylvain (or somebody as close to
that code, if anybody) could take a look...
> Slightly More Off-Heap Memtables
> --------------------------------
>
> Key: CASSANDRA-6694
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6694
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Benedict
> Assignee: Benedict
> Labels: performance
> Fix For: 2.1 beta2
>
>
> The Off Heap memtables introduced in CASSANDRA-6689 don't go far enough, as
> the on-heap overhead is still very large. It should not be tremendously
> difficult to extend these changes so that we allocate entire Cells off-heap,
> instead of multiple BBs per Cell (with all their associated overhead).
> The goal (if possible) is to reach an overhead of 16-bytes per Cell (plus 4-6
> bytes per cell on average for the btree overhead, for a total overhead of
> around 20-22 bytes). This translates to 8-byte object overhead, 4-byte
> address (we will do alignment tricks like the VM to allow us to address a
> reasonably large memory space, although this trick is unlikely to last us
> forever, at which point we will have to bite the bullet and accept a 24-byte
> per cell overhead), and 4-byte object reference for maintaining our internal
> list of allocations, which is unfortunately necessary since we cannot safely
> (and cheaply) walk the object graph we allocate otherwise, which is necessary
> for (allocation-) compaction and pointer rewriting.
> The ugliest thing here is going to be implementing the various CellName
> instances so that they may be backed by native memory OR heap memory.
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