Jeremiah Jordan created CASSANDRA-11738:
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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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