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https://issues.apache.org/jira/browse/CASSANDRA-9227?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14509095#comment-14509095
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Aleksey Yeschenko commented on CASSANDRA-9227:
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bq. Why does a large number of clients make token-aware routing impractical?
Because of the unsustainable number of connections to maintain, mostly.
> Support num_tokens: 0
> ---------------------
>
> Key: CASSANDRA-9227
> URL: https://issues.apache.org/jira/browse/CASSANDRA-9227
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Rick Branson
>
> num_tokens: 0 would allow serving proxy traffic on non-storage machines.
> Token-aware routing does improve the cost of proxying a bit, but it only
> works in cases where CL<=1 for reads, and doesn't really improve the write
> situation. For some installations, token-aware routing is also impractical,
> such as when there are a very large number of clients.
> For use cases that are throughput-bound rather than storage-bound, this would
> allow running CPU-intensive proxy work on cheaper "diskless" machines.
> Proxies could also be installed on the same machine as the client or on
> separate "edge" machines that are closer to the client than the storage
> nodes. In my observation, anywhere between 25-50% of a node's CPU is spent on
> proxy work, depending on the workload.
> I say "diskless" because they can't be truly diskless as they would have to
> store hints. Hint storage can use cheap spinning disks or small solid-state
> drives instead of expensive big disk arrays or big SSDs.
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