Improve counter disk usage
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Key: CASSANDRA-2455
URL: https://issues.apache.org/jira/browse/CASSANDRA-2455
Project: Cassandra
Issue Type: Improvement
Reporter: Stu Hood
Counter values currently use a huge amount of space on disk:
{{(header + length + RF * (nodeid + count + clock)) bytes}}
or
{{(2 + 2 + RF * (16 + 8 + 8)) bytes}}
Type specific compression (as on CASSANDRA-2398) is a long term solution to
this problem, but we need a short term fix to make a large volume of counters
possible.
The largest and most redundant part of the counter is the nodeid, which is now
16 bytes per replica. One proposed fix would be keep a per-sstable dictionary
of all replica sets, and to assume the replicas are sorted by nodeid in the
counter value. This would allow us to encode the replica as a single integer in
the counter value, and to use it to look up the replica set in the dictionary.
Assuming an integer replica set id, you could allow for 2^32 replica changes
with 4 total bytes of overhead in each counter:
{{(header + length + replicasetid + RF (count + clock)) bytes}}
or
{{(2 + 2 + 4 + RF * (8 + 8)) bytes}}
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