[jira] [Created] (CASSANDRA-6507) counters++ get rid of logical clock in global shards

["Aleksey Yeschenko (JIRA)" <ji...@apache.org>]

Aleksey Yeschenko created CASSANDRA-6507:
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             Summary: counters++ get rid of logical clock in global shards
                 Key: CASSANDRA-6507
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6507
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Aleksey Yeschenko
            Assignee: Aleksey Yeschenko
            Priority: Minor
             Fix For: 2.1


In CASSANDRA-6504 the global shards still follow the {count, logical clock} pattern of the legacy shards. We could store the {increments, decrements} tuple in the shard instead, and for reconcile, instead of relying on the logical clock, pick the largest value of `increments` and `decrements` of the two shards, and use that.

E.g., shard1: {2000, 1001} (total 999), shard2: {2001, 1000} (total 1001). reconciled = {max(2000, 2001), max(1001, 1000)} = {2001, 1001} (total 1000).

While scenarios like this generally shouldn't happen post CASSANDRA-6504, this change costs us nothing, and makes issues like CASSANDRA-4417 theoretically impossible	. This also makes our new implementation directly follow the http://hal.inria.fr/docs/00/55/55/88/PDF/techreport.pdf white paper.



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