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Pavel Yaskevich edited comment on CASSANDRA-6694 at 4/25/14 8:49 PM:
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1-2, 5-7 I will address once the main functionality is settled.
bq. AbstractCell.localCopy(..MemtableAllocator) needs to be overridden; as it
is you'll always get a regular Cell back
Good catch, I forgot to change that before I pushed. Have amended it to the
original allocator commit and force pushed to my branch, so it's available.
bq. You're still using static method implementations, it looks like? Cell.diff
and Cell.reconcile
Yes, just two of them, as I mentioned earlier, for the CounterCell because it
has to return BufferCounterCell, no point of copying those methods for now.
was (Author: xedin):
1-2, 5-7 I will address once the main functionality is settled.
bq. AbstractCell.localCopy(..MemtableAllocator) needs to be overridden; as it
is you'll always get a regular Cell back
Good catch, I forgot to change that before I pushed. Have amended it to the
original allocator commit and force pushed to my branch, so it's available.
> 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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