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From "Chris Burroughs (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4705) Speculative execution for CL_ONE
Date Fri, 05 Oct 2012 17:04:04 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13470461#comment-13470461
] 

Chris Burroughs commented on CASSANDRA-4705:
--------------------------------------------

> Looks like metrics-core exposes 75, 95, 97, 99 and 99.9

Reporters have a limited set (ie you can't generate new values that will pop up in jmx on
the fly), but in code you should be able to get at any percentile you want: https://github.com/codahale/metrics/blob/2.x-maintenance/metrics-core/src/main/java/com/yammer/metrics/stats/Snapshot.java#L54
                
> 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
>         Attachments: 0001-CASSANDRA-4705.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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