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Vijay commented on CASSANDRA-4705:
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No, DSnitch watches for the latency but doesn't do the later.... It wont
speculate/execute duplicate requests to another host, if the response times are
> x%.
I think this patch will be in addition to dsnitch, something like Jonathan
posted in 2540
{quote}
I like the approach described in
http://static.googleusercontent.com/external_content/untrusted_dlcp/research.google.com/en/us/people/jeff/Berkeley-Latency-Mar2012.pdf
of doing "backup" requests if the original doesn't reply within N% of normal.
{quote}
> 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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