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https://issues.apache.org/jira/browse/CASSANDRA-7282?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16533127#comment-16533127
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Benedict commented on CASSANDRA-7282:
-------------------------------------

Hi Michael,

I'll try to review this properly, as I find time.  A couple of things leap out 
to me though:
 # While we certainly need to handle out of range tokens, we should try harder 
to minimise their occurrence, by switching memtable on a token range change.  
Ideally we would switch before this new token range actually takes effect in 
the case of an expansion; whether or not it makes sense to defer a token range 
removal probably needs some thought.
 # A range tree is probably overkill.  Why not binary search over an array?

> Faster Memtable map
> -------------------
>
>                 Key: CASSANDRA-7282
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7282
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Benedict
>            Assignee: Michael Burman
>            Priority: Major
>              Labels: performance
>             Fix For: 4.x
>
>         Attachments: jasobrown-sample-run.txt, profile.yaml, reads.svg, 
> run1.svg, writes.svg
>
>
> Currently we maintain a ConcurrentSkipLastMap of DecoratedKey -> Partition in 
> our memtables. Maintaining this is an O(lg(n)) operation; since the vast 
> majority of users use a hash partitioner, it occurs to me we could maintain a 
> hybrid ordered list / hash map. The list would impose the normal order on the 
> collection, but a hash index would live alongside as part of the same data 
> structure, simply mapping into the list and permitting O(1) lookups and 
> inserts.
> I've chosen to implement this initial version as a linked-list node per item, 
> but we can optimise this in future by storing fatter nodes that permit a 
> cache-line's worth of hashes to be checked at once,  further reducing the 
> constant factor costs for lookups.



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