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From "Michael Kjellman (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-14293) Speculative Retry Policy Should Support Specifying MIN/MAX of 2 PERCENTILE and FIXED Policies
Date Wed, 07 Mar 2018 06:02:00 GMT
Michael Kjellman created CASSANDRA-14293:
--------------------------------------------

             Summary: 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


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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