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From "Brandon Williams (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4066) Cassandra cluster stops responding on time change (scheduling not using monotonic time?)
Date Tue, 20 Mar 2012 18:25:40 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4066?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13233648#comment-13233648
] 

Brandon Williams commented on CASSANDRA-4066:
---------------------------------------------

I can confirm that this is indeed the GossipTask no longer running when the clock is pushed
backward far enough.  As you mention, we use SES extensively and likely all those timed tasks
have also quit firing, which could lead to an untold amount of confusion if we special-cased
gossip, since there would be no immediate red flag to indicate a problem.  Starting a node
far in the future has other consequences too, such as CASSANDRA-3654.  I think I would rather
see the UAE and know that my machines have connectivity to identify this problem and fix it
correctly.

Even if we do special-case the GossipTask, we'll also need to fix LoadBroadcaster so we don't
end up with a broken view of the load on the ring, and at that point it feels like a slippery
slope where we need to fix everything, or fail as quickly as possible, which is what the current
behavior does.

Also an interesting thing to note is that the node still replies to gossip syn messages with
a gossip ack, but because we only update the FD on a version/generation change, and because
LoadBroadcaster is also broken the node has no reason to generate new versions, it remains
seen as down to the other nodes.  If LB did happen to work, we'd see the node flap every 90
seconds.
                
> Cassandra cluster stops responding on time change (scheduling not using monotonic time?)

> -----------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-4066
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4066
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>         Environment: Linux; CentOS6 2.6.32-220.4.2.el6.x86_64
>            Reporter: David Daeschler
>            Assignee: Brandon Williams
>            Priority: Minor
>              Labels: gossip
>             Fix For: 1.1.1
>
>
> The server installation I set up did not have ntpd installed in the base installation.
When I noticed that the clocks were skewing I installed ntp and set the date on all the servers
in the cluster. A short time later, I started getting UnavailableExceptions on the clients.

> Also, one sever seemed to be unaffected by the time change. That server happened to have
it's time pushed forward, not backwards like the other 3 in the cluster. This leads me to
believe something is running on a timer/schedule that is not monotonic.
> I'm posting this as a bug, but I suppose it might just be part of the communication protocols
etc for the cluster and part of the design. But I think the devs should be aware of what I
saw.
> Otherwise, thank you for a fantastic product. Even after restarting 75% of the cluster
things seem to have recovered nicely.

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