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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9536) The failure detector becomes more sensitive when the network is flakey
Date Tue, 02 Jun 2015 21:42:50 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9536?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14569811#comment-14569811
] 

Jonathan Ellis commented on CASSANDRA-9536:
-------------------------------------------

Curious if [~jasobrown] has any thoughts here.

> 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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