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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-6930) Dynamic Snitch isWorthMergingForRangeQuery Doesn't Handle Some Cases Optimally
Date Thu, 24 Jul 2014 20:37:38 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-6930?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jonathan Ellis updated CASSANDRA-6930:
--------------------------------------

    Reviewer: Tyler Hobbs

[~thobbs] to review

> Dynamic Snitch isWorthMergingForRangeQuery Doesn't Handle Some Cases Optimally
> ------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-6930
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6930
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Tyler Hobbs
>            Assignee: Ala' Alkhaldi
>            Priority: Minor
>              Labels: lhf
>             Fix For: 2.0.10
>
>         Attachments: 9630-v1.txt
>
>
> I was investigating slow responses for queries like {{select * from system.peers}} and
noticed that the dynamic endpoint snitch was reporting that the query was _not_ worth merging.
 In this case, the local host had a score of 0, so {{return maxMerged < maxL1 + maxL2}}
was returning false.  I believe using a {{<=}} condition is the proper fix there.
> Additionally, because scores are looked up three separate times, this method is a prone
to race conditions.  I don't think it's worth fixing the race condition for a multi-node scenario,
but at least in the single-node case, we can immediately return true and avoid any race conditions
that would cause it to erroneously return false.



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