Sylvain Lebresne created CASSANDRA-10409:
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Summary: 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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