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https://issues.apache.org/jira/browse/CASSANDRA-5019?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13536971#comment-13536971
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Sylvain Lebresne commented on CASSANDRA-5019:
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Actually, thinking about this issue a bit more, I'm wondering: what is it we
expect to win here?
Because we will still need to allocate one FlyweightColumn object per actual
column. So in terms of sheer number of allocated objects, we'll have the same
number (in fact we'll even have marginally more ojbects since we'll have to
allocate the FlyweightColumns names, values and timestamps arrays).
Now it's true that the memory layout will be slightly different, with the
FlyweightColumn objects being slightly smaller than their Column counterpart
(though overall we won't allocate less memory), but I'm not sure it makes much
difference for the GC since the size difference is relatively minor. And on
the other side, the circular dependency of FlyweightColumns to it's child
FlyweightColumn might make the job of the GC a bit harder (it's more links to
explore). Overall, it's far from obvious to me that it would improve things in
a measurable way.
And doing that would also mess a bit with the ColumnSerializer, as we would
want it to create a flyweightColumn right away, meaning that it's not just an
alternative ISortedColumn implementation, the abstraction would leak out.
So am I missing something here and not understanding that idea at all?
> Still too much object allocation on reads
> -----------------------------------------
>
> Key: CASSANDRA-5019
> URL: https://issues.apache.org/jira/browse/CASSANDRA-5019
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Jonathan Ellis
> Fix For: 2.0
>
>
> ArrayBackedSortedColumns was a step in the right direction but it's still
> relatively heavyweight thanks to allocating individual Columns.
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