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https://issues.apache.org/jira/browse/CASSANDRA-7282?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14132906#comment-14132906
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Benedict commented on CASSANDRA-7282:
-------------------------------------
As already stated, I disagree. Always, when making these decisions, the
important factors are: 1) what workloads / portions of workloads are affected;
and 2) do we consider these common enough (or to become common enough) to
warrant inclusion?
Since we are very constrained on our hardware and workload generation, picking
a "realistic workload" that we can perform at best helps us rule out
regressions if it is not compatible with exhibiting the change. The important
question is simply: do we consider it likely it will impact other workloads we
are not capable of benchmarking, given the known information we have from
isolating its effect in a manner we _can_.
> 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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