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https://issues.apache.org/jira/browse/CASSANDRA-2455?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Stu Hood updated CASSANDRA-2455:
--------------------------------
Description:
Counter values currently use a huge amount of space on disk:
{code}
(header + length + RF * (nodeid + count + clock))
==
(2 + 2 + RF * (16 + 8 + 8)) bytes
{code}
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 improvement 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:
{code}
(header + length + replicasetid + RF (count + clock))
==
(2 + 2 + 4 + RF * (8 + 8)) bytes
{code}
was:
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}}
> Improve counter disk usage
> --------------------------
>
> 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:
> {code}
> (header + length + RF * (nodeid + count + clock))
> ==
> (2 + 2 + RF * (16 + 8 + 8)) bytes
> {code}
> 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 improvement 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:
> {code}
> (header + length + replicasetid + RF (count + clock))
> ==
> (2 + 2 + 4 + RF * (8 + 8)) bytes
> {code}
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