Details

    • Type: Wish
    • Status: Open
    • Priority: Major
    • Resolution: Unresolved
    • Fix Version/s: 4.x
    • Component/s: None
    • Labels:
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      Description

      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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              • Assignee:
                Unassigned
                Reporter:
                drew_kutchar Drew Kutcharian
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                • Created:
                  Updated: