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From "Brandon Williams (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3273) FailureDetector can take a very long time to mark a host down
Date Thu, 29 Sep 2011 18:13:45 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3273?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13117490#comment-13117490
] 

Brandon Williams commented on CASSANDRA-3273:
---------------------------------------------

bq. I thought only gossip heartbeats generate interval measurements, is that incorrect?

Heartbeats and generation changes.  I take back what I said though, it's not the versioning
reconnection, and it's not a problem with regard to making the FD take a long time to mark
a host down.

It is, however, possible to receive two intervals in a short amount of time, just due to timer
skew between the two hosts, but it can only happen once since after that they will be in sync
from the FD's perspective.

The net effect of this in the pathological case would be that the FD causes a host to be marked
down if the host suddenly becomes silent for a period of 4-5s after the FD receives the initial
(500ms) interval and then the short (1ms) one only.  


                
> FailureDetector can take a very long time to mark a host down
> -------------------------------------------------------------
>
>                 Key: CASSANDRA-3273
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3273
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Brandon Williams
>            Assignee: Brandon Williams
>
> There are two ways to trigger this:
> * Bring a node up very briefly in a mixed-version cluster and then terminate it
> * Bring a node up, terminate it for a very long time, then bring it back up and take
it down again
> In the first case, what can happen is a very short interval arrival time is recorded
by the versioning logic which requires reconnecting and can happen very quickly. This can
easily be solved by rejecting any intervals within a reasonable bound, for instance the gossiper
interval.
> The second instance is harder to solve, because what is happening is that an extremely
large interval is recorded, which is the time the node was left dead the first time.  This
throws off the mean of the intervals and causes it to take a much longer time than it should
to mark it down the second time.

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