[jira] [Created] (CASSANDRA-6506) counters++ split counter context shards into separate cells

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

Aleksey Yeschenko created CASSANDRA-6506:
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             Summary: counters++ split counter context shards into separate cells
                 Key: CASSANDRA-6506
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6506
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Aleksey Yeschenko
            Assignee: Aleksey Yeschenko
             Fix For: 2.1


This change is related to, but somewhat orthogonal to CASSANDRA-6504.

Currently all the shard tuples for a given counter cell are packed, in sorted order, in one binary blob. Thus reconciling N counter cells requires allocating a new byte buffer capable of holding the union of the two context's shards N-1 times.

For writes, in post CASSANDRA-6504 world, it also means reading more data than we have to (the complete context, when all we need is the local node's global shard).

Splitting the context into separate cells, one cell per shard, will help to improve this. We did a similar thing with super columns for CASSANDRA-3237. Incidentally, doing this split is now possible thanks to CASSANDRA-3237.

Doing this would also simplify counter reconciliation logic. Getting rid of old contexts altogether can be done trivially with upgradesstables.




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