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https://issues.apache.org/jira/browse/CASSANDRA-10409?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14934903#comment-14934903
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Sylvain Lebresne commented on CASSANDRA-10409:
----------------------------------------------
Pushed a patch for this
[here|https://github.com/pcmanus/cassandra/commits/10409] (with 2 commits: the
first one is the main patch, the 2nd one is a trivial optimization of
{{BTreeSet}} singleton constructor (which is particularly used by the new
specialization)).
> Specialize MultiCBuilder when building a single clustering
> ----------------------------------------------------------
>
> Key: CASSANDRA-10409
> URL: https://issues.apache.org/jira/browse/CASSANDRA-10409
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Sylvain Lebresne
> Assignee: Sylvain Lebresne
> Fix For: 3.x
>
>
> {{MultiCBuilder}} is used to build the {{Clustering}} and {{Slice.Bound}}
> used by queries. As the name implies, it's able to build multiple
> {{Clustering}}/{{Slice.Bound}} for when we have {{IN}}, but most queries
> don't use {{IN}} and in this (frequent) case, {{MultiCBuilder}} creates quite
> a bit more objects that would be necessary (it creates 2 lists for its
> {{elementsList}}, then a {{CBuilder}} and a {{BTreeSet.Builder}} (even though
> we know the resulting set will have only one element in this case)). Without
> being huge, this does show up as non entirely negligible when profiling some
> simple stress.
> We can easily know if the query has a {{IN}} and so we can know when only a
> single {{Clustering}}/{{Slice.Bound}} is built, and we can specialize the
> implementation in that case to be less wasteful.
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