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From "Sylvain Lebresne (JIRA)" <>
Subject [jira] [Created] (CASSANDRA-10409) Specialize MultiCBuilder when building a single clustering
Date Tue, 29 Sep 2015 09:13:04 GMT
Sylvain Lebresne created CASSANDRA-10409:

             Summary: Specialize MultiCBuilder when building a single clustering
                 Key: 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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