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Pavel Yaskevich commented on CASSANDRA-6694:
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bq. Well, these are still duplication - it is not clear as a result where the
definition of these behaviours live. If the semantics change in future, it may
introduce errors unnecessarily. Either way equals(), reconcile() and
validateFields() will still be issues. You don't seem to have implemented most
of these methods yet (looks like your code doesn't actually compile). These
methods are each non-trivial amounts of code duplication, equals() especially
so is we optimise it as you want to. CounterCell.diff() will also need to be
duplicated.
Most of the duplicated methods are methods with static behavior which is not
going to change e.g. isMarkedForDelete, getMarkedForDeleteAt or
serializationFlags. CounterCell.diff and reconcile are living in the interface
for now. I will address setPeer(long) problem and hashCode.
> 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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