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From "Jeff Jirsa (JIRA)" <>
Subject [jira] [Assigned] (CASSANDRA-6412) Custom creation and merge functions for user-defined column types
Date Sat, 04 Apr 2015 05:11:33 GMT


Jeff Jirsa reassigned CASSANDRA-6412:

    Assignee: Jeff Jirsa

> Custom creation and merge functions for user-defined column types
> -----------------------------------------------------------------
>                 Key: CASSANDRA-6412
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Nicolas Favre-Felix
>            Assignee: Jeff Jirsa
> This is a proposal for a new feature, mapping custom types to Cassandra columns.
> These types would provide a creation function and a merge function, to be implemented
in Java by the user.
> This feature relates to the concept of CRDTs; the proposal is to replicate "operations"
on these types during write, to apply these operations internally during merge (Column.reconcile),
and to also merge their values on read.
> The following operations are made possible without reading back any data:
> * MIN or MAX(value) for a column
> * First value for a column
> * Count Distinct
> * HyperLogLog
> * Count-Min
> And any composition of these too, e.g. a Candlestick type includes first, last, min,
and max.
> The merge operations exposed by these types need to be commutative; this is the case
for many functions used in analytics.
> This feature is incomplete without some integration with CASSANDRA-4775 (Counters 2.0)
which provides a Read-Modify-Write implementation for distributed counters. Integrating custom
creation and merge functions with new counters would let users implement complex CRDTs in
Cassandra, including:
> * Averages & related (sum of squares, standard deviation)
> * Graphs
> * Sets
> * Custom registers (even with vector clocks)
> I have a working prototype with implementations for min, max, and Candlestick at
- I'd appreciate any feedback on the design and interfaces.

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