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From "Michael Kjellman (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-14293) Speculative Retry Policy Should Support Specifying MIN/MAX of 2 PERCENTILE and FIXED Policies
Date Thu, 22 Mar 2018 19:29:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-14293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16410167#comment-16410167
] 

Michael Kjellman commented on CASSANDRA-14293:
----------------------------------------------

changes look fine to me. let's get this committed on to trunk to start with so we can start
working on a 3.0 version...

> Speculative Retry Policy Should Support Specifying MIN/MAX of 2 PERCENTILE and FIXED
Policies
> ---------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-14293
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14293
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Michael Kjellman
>            Assignee: Michael Kjellman
>            Priority: Major
>             Fix For: 4.x
>
>
> Currently the Speculative Retry Policy takes a single string as a parameter, this can
be NONE, ALWAYS, 99PERCENTILE (PERCENTILE), 50MS (CUSTOM).
> The problem we have is when a single host goes into a bad state this drags up the percentiles.
This means if we are set to use p99 alone, we might not speculate when we intended to to
because the value at the specified percentile has gone so high.
> As a fix we need to have support for something like min(99percentile,50ms)
> this means if the normal p99 for the table is <50ms, we will still speculate at this
value and not drag the happy path tail latencies up... but if the p99th goes above what we
know we should never exceed we use that instead.



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