[jira] [Created] (CASSANDRA-9536) The failure detector becomes more sensitive when the network is flakey

["Ron Kuris (JIRA)" <ji...@apache.org>]

Ron Kuris created CASSANDRA-9536:
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             Summary: The failure detector becomes more sensitive when the network is flakey
                 Key: CASSANDRA-9536
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9536
             Project: Cassandra
          Issue Type: Bug
          Components: Core
            Reporter: Ron Kuris


I added considerable instrumentation into the failure detector, and then blocked port 7000 for a random 5-6 second interval, then resumed traffic for the same amount of time, with a script like:
{code}while :
do
   iptables -A INPUT -p tcp --destination-port 7000 -j DROP
        v=$[100 + (RANDOM % 100)]$[1000 + (RANDOM % 1000)]
        s=5.${v:1:2}${v:4:3}
        echo offline for $s
        sleep $s
        iptables -F
        v=$[100 + (RANDOM % 100)]$[1000 + (RANDOM % 1000)]
        s=5.${v:1:2}${v:4:3}
        echo online for $s
        sleep $s
done{code}
When I do this, I watch the values being reported to the FailureDetector. The median actually goes down, as low as 850ms. The reason is that the very slow packets are not recorded (they exceed MAX_INTERVAL_IN_NANO which is 2 seconds) and the retransmitted packets arrive very quickly in succession, lowering the overall average.

Once the average is lowered, the node becomes much more sensitive to shorter outages. If you run this code for a while, the average drops down to 800ms or less, which means that the node will go down 20% quicker than expected.



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