[jira] [Commented] (CASSANDRA-4705) Speculative execution for CL_ONE

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

    [ https://issues.apache.org/jira/browse/CASSANDRA-4705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13461464#comment-13461464 ] 

Brandon Williams commented on CASSANDRA-4705:
---------------------------------------------

bq. It would be nice to watch for latency and execute an additional request to a different node

Isn't this what the dsnitch does to some degree?
                
> Speculative execution for CL_ONE
> --------------------------------
>
>                 Key: CASSANDRA-4705
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4705
>             Project: Cassandra
>          Issue Type: Improvement
>    Affects Versions: 1.2.0
>            Reporter: Vijay
>            Assignee: Vijay
>            Priority: Minor
>
> When read_repair is not 1.0, we send the request to one node for some of the requests. When a node goes down or when a node is too busy the client has to wait for the timeout before it can retry. 
> It would be nice to watch for latency and execute an additional request to a different node, if the response is not received within average/99% of the response times recorded in the past.
> CASSANDRA-2540 might be able to solve the variance when read_repair is set to 1.0
> 1) May be we need to use metrics-core to record various Percentiles
> 2) Modify ReadCallback.get to execute additional request speculatively.

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