[jira] [Created] (CASSANDRA-9110) Bounded/RingBuffer CQL Collections

["Jim Plush (JIRA)" <ji...@apache.org>]

Jim Plush created CASSANDRA-9110:
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             Summary: Bounded/RingBuffer CQL Collections
                 Key: CASSANDRA-9110
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9110
             Project: Cassandra
          Issue Type: New Feature
          Components: Core
            Reporter: Jim Plush
            Priority: Minor


Feature Request:
I've had frequent use cases for bounded and RingBuffer based collections. 

For example: 
I want to store the first 100 times I've see this thing.
I want to store the last 100 times I've seen this thing.

Currently that means having to do application level READ/WRITE operations and we like to keep some of our high scale apps to write only where possible. 

While probably expensive for exactly N items an approximation should be good enough for most applications. Where N in our example could be 100 or 102, or even make that tunable on the type or table. 

For the RingBuffer example, consider I only want to store the last N login attempts for a user. Once N+1 comes in it issues a delete for the oldest one in the collection. 

A potential implementation idea, given the rowkey would live on a single node would be to have an LRU based counter cache (tunable in the yaml settings in MB) that keeps a current count of how many items are already in the collection for that rowkey. If > than bound, toss.


something akin to:
CREATE TABLE users (
  user_id text PRIMARY KEY,
  first_name text,
  first_logins set<text, 100, oldest>
  last_logins set<text, 100, newest>
);





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