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https://issues.apache.org/jira/browse/CASSANDRA-7282?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14132913#comment-14132913
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Branimir Lambov commented on CASSANDRA-7282:
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This makes sense. Thanks for clarifying, the fact that the list is ordered by
the Token escaped me. Since this is the case, should we restrict this method to
Murmur tokens only? For anything that sorts naturally we could just grab the
first four bytes. I wouldn't even call this a hashCode to avoid the confusion,
perhaps an "ordering key" or "ordering prefix"?
I would still change the condition in the preface to use non-strict inequality,
though, because cropping tokens to 32 bits will introduce collisions.
> Faster Memtable map
> -------------------
>
> Key: CASSANDRA-7282
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7282
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Benedict
> Assignee: Benedict
> Labels: performance
> Fix For: 3.0
>
> Attachments: 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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