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Benedict commented on CASSANDRA-6689:
-------------------------------------
I've uploaded a patch
[here|https://github.com/belliottsmith/cassandra/tree/offheap.merge]
In the simplest terms this boils down to a new off heap allocator. However it
is much more involved than that, as we need to now manage the life cycle of the
memory in question.
I won't go into excessive detail here, because I have tried to do so as much as
possible in the code itself. For full details see the comments in
OffHeapCleaner, RefAction/Referrer, OffHeapAllocator, OffHeapRegion.
The basic thrust of the approach is that we guard accesses to the memory
through the OpOrder synchronisation primitive introduced with the
CASSANDRA-5549. However to prevent stalls and make management of the memory
easier, we have some further stages to the lifecycle which are much more
GC-like. A corollary is that we also effectively perform GC of the data in the
memtable, so that space that is no longer needed as a result of overwritten
records can be made available again without first flushing the memtable.
> Partially Off Heap Memtables
> ----------------------------
>
> Key: CASSANDRA-6689
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6689
> Project: Cassandra
> Issue Type: New Feature
> Reporter: Benedict
> Assignee: Benedict
> Fix For: 2.1
>
>
> Move the contents of ByteBuffers off-heap for records written to a memtable.
> (See comments for details)
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