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https://issues.apache.org/jira/browse/CASSANDRA-9536?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14569894#comment-14569894
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Ron Kuris commented on CASSANDRA-9536:
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One additional thought here is that it's probably fairly safe to record some
extra 2 values since that errs on the side of not bringing the node down as
fast. In fact, the first sample received is automatically recorded at value "2"
so it's kind of a known quantity. The average quickly drops as values close to
1 are added to the list.
> 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: Improvement
> Components: Core
> Reporter: Ron Kuris
> Priority: Minor
> Fix For: 2.2.x
>
>
> 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
> mean 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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