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https://issues.apache.org/jira/browse/CASSANDRA-14293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16389067#comment-16389067
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Michael Kjellman commented on CASSANDRA-14293:
----------------------------------------------

Ideally we'd express this a bit nicer by having the speculative_retry table 
config option as a map, but we're bound by legacy here and have no way to 
migrate and change this with the current state of schema. So, ultimately we'll 
still need to do a bunch of string parsing but we can at least get the 
functionality we need with the following function-esque syntax (examples):

max(99.9p,50ms)

MIN(50MS,90PERCENTILE)

> 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
>
> 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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