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Tyler Hobbs commented on CASSANDRA-7982:
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bq. why do token ranges come into picture for secondary index scan?
We need to fetch results in token order to enable things like paging and
splitting up jobs (e.g. Hadoop). If we knew that we wouldn't hit the LIMIT for
the query (or page size), we could absolutely have each node read everything
and ignore token ranges, but there's no way to guarantee that.
I suggest looking into upgrading to 2.1 at some point if secondary index
performance is important to you. CASSANDRA-1337 will help there, and this
ticket is just a minor optimization on top of that.
> Batch multiple range requests that are going to the same replica
> -----------------------------------------------------------------
>
> Key: CASSANDRA-7982
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7982
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Jay Patel
> Assignee: Jay Patel
> Fix For: 3.0
>
> Attachments: output1.txt
>
>
> In case of VNode and secondary index query, coordinator sends multiple range
> requests to the same replica. For example, in the attached tracing session
> (output1.txt), coordinator(192.168.51.22) sends multiple requests to
> 192.168.51.25. Why can't we batch all the requests to the same replica to
> avoid multiple round trips? I think this is not the issue with non-vnode
> cluster where each node has one big range (+ replica ranges), instead of many
> small ranges.
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