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https://issues.apache.org/jira/browse/CASSANDRA-8861?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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C. Scott Andreas updated CASSANDRA-8861:
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Component/s: CQL
> HyperLogLog Collection Type
> ---------------------------
>
> Key: CASSANDRA-8861
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8861
> Project: Cassandra
> Issue Type: New Feature
> Components: CQL
> Reporter: Drew Kutcharian
> Priority: Major
> Fix For: 4.x
>
>
> Considering that HyperLogLog and its variants have become pretty popular in
> analytics space and Cassandra has "read-before-write" collections (Lists), I
> think it would not be too painful to add support for HyperLogLog "collection"
> type. They would act similar to CQL 3 Sets, meaning you would be able to
> "set" the value and "add" an element, but you won't be able to remove an
> element. Also, when getting the value of a HyperLogLog collection column,
> you'd get the cardinality.
> There are a couple of good attributes with HyperLogLog which fit Cassandra
> pretty well.
> - Adding an element is idempotent (adding an existing element doesn't change
> the HLL)
> - HLL can be thought of as a CRDT, since we can safely merge them. Which
> means we can merge two HLLs during read-repair. But if that's too much work,
> I guess we can even live with LWW since these counts are "estimates" after
> all.
> There is already a proof of concept at:
> http://vilkeliskis.com/blog/2013/12/28/hacking_cassandra.html
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