[jira] [Comment Edited] (CASSANDRA-4705) Speculative execution for Reads

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-4705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13565049#comment-13565049 ] 

Jonathan Ellis edited comment on CASSANDRA-4705 at 1/29/13 3:53 AM:
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(Also, changing SimpleCondition scares me a bit so let's pull that out to a separate ticket if it's necessary -- I took out those changes in my branch.)
                
      was (Author: jbellis):
    (Also, changing SimpleCondition scares me a bit so let's pull that out to a separate ticket if it's necessary.)
                  
> Speculative execution for Reads
> -------------------------------
>
>                 Key: CASSANDRA-4705
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4705
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Vijay
>            Assignee: Vijay
>             Fix For: 2.0
>
>         Attachments: 0001-CASSANDRA-4705.patch, 0001-CASSANDRA-4705-v2.patch, 0001-CASSANDRA-4705-v3.patch, 0001-Refactor-to-introduce-AbstractReadExecutor.patch, 0002-Add-Speculative-execution-for-Row-Reads.patch
>
>
> 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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