Drew Kutcharian created CASSANDRA-8861:
------------------------------------------
Summary: HyperLogLog Collection Type
Key: CASSANDRA-8861
URL: https://issues.apache.org/jira/browse/CASSANDRA-8861
Project: Cassandra
Issue Type: Wish
Reporter: Drew Kutcharian
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
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
