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https://issues.apache.org/jira/browse/CASSANDRA-6694?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13973633#comment-13973633
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Benedict edited comment on CASSANDRA-6694 at 4/18/14 12:36 AM:
---------------------------------------------------------------
Thanks. Although it looks like you haven't updated any of the offsets to work
with the new layout?
As to the other changes you've made: I do not like the pollution of
PoolAllocator with supportsNative() and allocateNative(). Since this branch is
supposed to be pushing idiomatic Java usage, let's stick to using interfaces
for specialisation since we can.
was (Author: benedict):
Thanks. Although it looks like you haven't updated any of the offsets to work
with the new layout?
As to the other changes you've made: I do not like the pollution of
PoolAllocator with supportsNative(). Since this branch is supposed to be
pushing idiomatic Java usage, let's stick to using interfaces for
specialisation since we can.
> 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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