[jira] [Created] (CASSANDRA-5173) Provide a mechanism to notify listeners when a mutation has occurred (or certain types of mutations have happened)

["B. Todd Burruss (JIRA)" <ji...@apache.org>]

B. Todd Burruss created CASSANDRA-5173:
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             Summary: Provide a mechanism to notify listeners when a mutation has occurred (or certain types of mutations have happened)
                 Key: CASSANDRA-5173
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5173
             Project: Cassandra
          Issue Type: Improvement
            Reporter: B. Todd Burruss
            Priority: Minor


This is related to CASSANDRA-1311 but much less complicated.  I have had the desire in the past where my application needed to react to mutations on Cassandra that have come from other DCs.  Essentially using Cassandra as the storage system of record, but also using its replication as a "bus".

An example of a straightforward use case is a read through caching system that can be more intelligent about its data than Cassandra's built in caching - providing better performance.  One caching system per DC.  The DC to DC replication in Cassandra is nice to keep data in sync, but the external caching system must know when a mutation comes from another DC and mark its data as dirty - or do whatever.  Combine these notifications with TTLs on the cache and you have a fairly robust external caching integration with Cassandra!

To get this integration, the external cache would register a "listener" (in the same JVM as Cassandra) for the types of mutations it is interested in, and receive an event when the conditions are met.  after that it is the job of the listener to do what it needs.

I created a patch on 1.1.4, but then the business decided on another direction.  If this is still interesting to the community I can rebase to 1.2 and post the patch, but my use case has since passed and I will probably not have time to maintain it.

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