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Date: Sun, 30 Nov 2014 23:18:13 +0000 (UTC)
From: "Benedict (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (CASSANDRA-6976) Determining replicas to query
 is very slow with large numbers of nodes or vnodes
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    [ https://issues.apache.org/jira/browse/CASSANDRA-6976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14229269#comment-14229269 ] 

Benedict commented on CASSANDRA-6976:
-------------------------------------

On second thoughts, ignore that sentiment entirely. We don't really have any concept of a "lookup table", and we'll have to address that directly when we introduce enum types which is a better place. 

I guess what really bugs me about this, and what I assumed would be related to the problem (but patently can't given the default behaviour) is that after calculating natural endpoints, we then sort them (based on a couple of hashmap lookups for each end point) for every token range, and also for every single normal query. This sort is performed over RF*DC items in either case, even for queries routed directly to the owning node with CL ONE. I was hoping we'd fix that as a result of this work, since that's a lot of duplicated effort, but that hardly seems sensible now. What we definitely _should_ do, though, is make sure we're (in general) benchmarking behaviour over common config, as our default test configuration is not at all representative.

> Determining replicas to query is very slow with large numbers of nodes or vnodes
> --------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-6976
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6976
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Benedict
>            Assignee: Ariel Weisberg
>              Labels: performance
>         Attachments: GetRestrictedRanges.java, jmh_output.txt, jmh_output_murmur3.txt, make_jmh_work.patch
>
>
> As described in CASSANDRA-6906, this can be ~100ms for a relatively small cluster with vnodes, which is longer than it will spend in transit on the network. This should be much faster.


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