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https://issues.apache.org/jira/browse/CASSANDRA-7282?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16533884#comment-16533884
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Benedict commented on CASSANDRA-7282:
-------------------------------------
Great, thanks. The mismatch in expectations is probably because this is not
the optimal way to implement a binary search variant.
Ideally it would have two (or three) backing arrays, as opposed to a backing
array of nodes. One primitive array of one side of bounds (e.g. lower bounds)
to search on; another of keys, and another primitive array of the opposing
bounds to filter results (or if the bounds are encoded in the keys already,
that could be skipped).
Do you mind adding that variant to the comparison?
> 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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