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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11738) Re-think the use of Severity in the DynamicEndpointSnitch calculation
Date Thu, 19 May 2016 03:16:12 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11738?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15290389#comment-15290389
] 

Jonathan Ellis commented on CASSANDRA-11738:
--------------------------------------------

It could, but how would you decide when to use "load" and when to use directly measured latency?

> 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: Improvement
>            Reporter: Jeremiah Jordan
>             Fix For: 3.x
>
>
> 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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