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https://issues.apache.org/jira/browse/CASSANDRA-6694?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13973534#comment-13973534
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Pavel Yaskevich edited comment on CASSANDRA-6694 at 4/17/14 10:56 PM:
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Ok, hashCode and setPeer changes are now pushed to the same branch,
AbstractNativeCell is independent of NativeAllocation now because
NativeAllocator returns aligned peer directly, which allows "peer" field to be
made final in AbstractNativeCell. Also I have pushed set/get logic for data
size associated with the pointer to the NativeAllocator as it's basically it's
metadata, IMO it's a bit cleaner comparing to how that is done in Benedict's
branch where NativeAllocation tracks pointer alignment to size (internalPeer()
\{ return peer + 4; \}) but NativeAllocator takes care of allocating 4
additional bytes to requested size.
was (Author: xedin):
Ok, hashCode and setPeer changes are now pushed to the same branch,
AbstractNativeCell is independent of NativeAllocation now because
NativeAllocator returns aligned peer directly, which allows "peer" field to be
made final in AbstractNativeCell. Also I have pushed set/get logic for data
size associated with the pointer to the NativeAllocator as it's basically it's
metadata, IMO it's a bit cleaner comparing to how that is done in Benedict's
branch where NativeAllocation tracks pointer alignment to size (internalPeer()
{ return peer + 4; }) but NativeAllocator takes care of allocating 4 additional
bytes to requested size.
> 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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