[jira] [Commented] (CASSANDRA-6930) Dynamic Snitch isWorthMergingForRangeQuery Doesn't Handle Some Cases Optimally

["Ala' Alkhaldi (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-6930?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14073523#comment-14073523 ] 

Ala' Alkhaldi commented on CASSANDRA-6930:
------------------------------------------

The inequality was fixed as part of [CASSANDRA-7535|https://issues.apache.org/jira/browse/CASSANDRA-7535]. The single node case is handled in 9630-v1.txt.

> 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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