[jira] [Commented] (CASSANDRA-2662) Nodes get ignored by dynamic snitch when read repair chance is zero

["Brandon Williams (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-2662?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13035431#comment-13035431 ] 

Brandon Williams commented on CASSANDRA-2662:
---------------------------------------------

To clarify what this patch does: on the first round, behavior is unchanged, it will fall back to the subsnitch as usual.  On the second round however, the nodes will have scores so the dynamic snitch will determine the best host.  This seems like a good idea, but I think we should proceed cautiously with regard to CASSANDRA-1314.  This is certainly going to blow the cache on the second round, since the unpinned hosts at zero are guaranteed to be ranked higher than the pinned one.  However, in the current implementation, the badness threshold in CASSANDRA-1519 can never take effect at RR = 0 since the scores of the other replicas will always be null, and thus diversion to the subsnitch will always occur, returning the pinned replica.  With this patch, the second replica is likely to end up being the pinned one, which I think will be ok, as long as all coordinators agree, though this might not always be the case.

> Nodes get ignored by dynamic snitch when read repair chance is zero
> -------------------------------------------------------------------
>
>                 Key: CASSANDRA-2662
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2662
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 0.7.6
>            Reporter: Daniel Doubleday
>            Priority: Trivial
>         Attachments: dynsnitch.patch
>
>
> DynamicEndpointSnitch falls back to subsnitch when one of the scores of the endpoints being compared is missing.
> This leads to a stable order of hosts until reads will lead to recorded scores. 
> If setting read repair chance to 0 and reads are performed with quorum then (rf - # quorum nodes) will never get reads.

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