Ron Kuris created CASSANDRA-9536:
------------------------------------
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.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
