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From "Jeremiah Jordan (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-11738) Re-think the use of Severity in the DynamicEndpointSnitch calculation
Date Mon, 09 May 2016 16:23:12 GMT
Jeremiah Jordan created CASSANDRA-11738:
-------------------------------------------

             Summary: Re-think the use of Severity in the DynamicEndpointSnitch calculation
                 Key: CASSANDRA-11738
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11738
             Project: Cassandra
          Issue Type: Bug
            Reporter: Jeremiah Jordan


CASSANDRA-11737 was opened to allow completely disabling the use of severity in the DynamicEndpointSnitch
calculation, but that is a pretty big hammer.  There is probably something we can do to better
use the score.

The issue seems to be that severity is given equal weight with latency in the current code,
also that severity is only based on disk io.  If you have a node that is CPU bound on something
(say catching up on LCS compactions because of bootstrap/repair/replace) the IO wait can be
low, but the latency to the node is high.

Some ideas I had are:
1. Allowing a yaml parameter to tune how much impact the severity score has in the calculation.
2. Taking CPU load into account as well as IO Wait (this would probably help in the cases
I have seen things go sideways)
3. Move the -D from CASSANDRA-11737 to being a yaml level setting
4. Go back to just relying on Latency and get rid of severity all together.  Now that we have
rapid read protection, maybe just using latency is enough, as it can help where the predictive
nature of IO wait would have been useful.



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