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https://issues.apache.org/jira/browse/CASSANDRA-6694?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13963531#comment-13963531
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Pavel Yaskevich commented on CASSANDRA-6694:
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bq. More (multiple implementation) virtual method invocations (as shown by
CASSANDRA-6993 this can have meaningfully negative performance implications)
I'm getting mixed signals here, are you claiming that JVM does a bad job or OOP
is broken in general? Also CASSANDRA-6993 seems to point to a different problem.
bq. Major refactor of AbstractType hierarchy to prevent bytebuffer allocation
on comparison
I don't see a problem with this if it spares most of the changes in allocators
and Cell*/DecoratedKey rewrites.
bq. More object allocation in the request threads due to having to re-pack all
of any parameters into a Cell with a single buffer, as opposed to just dropping
them in place
We can have a Cell separate implementation with multiple buffers as Thrift
allocates them anyway which we are going to be transformed to linear ones once
they get into memtable as we have to reallocate there.
bq. At which point it would make most sense to refactor (and mostly eliminate)
the entirety of CASSANDRA-5417, as we're almost always pumping the result
straight into a Cell anyway, so extracting the components into separate buffers
and repacking them into a single buffer in the Cell is very wasteful
Is it good or bad to refactor it? [~slebresne]/[~jbellis] WDYT?
> 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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