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https://issues.apache.org/jira/browse/ZOOKEEPER-366?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benjamin Reed updated ZOOKEEPER-366:
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Attachment: ZOOKEEPER-366.patch
this patch smooths out the effect of a radical time change by always sleeping
at least 1/2 tickTime. this means that if we really needed to do a big jump
forward, it will take up 1/2 of the jump to converge on the real time. because
clients ping for idle times of 1/3 the timeout, there should be few sessions
that expire. we could reduce that number, but take even longer to converge if
we always sleep at least 3/4 of the tickTime.
> Session timeout detection can go wrong if the leader system time changes
> ------------------------------------------------------------------------
>
> Key: ZOOKEEPER-366
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-366
> Project: Zookeeper
> Issue Type: Bug
> Reporter: Benjamin Reed
> Assignee: Benjamin Reed
> Attachments: ZOOKEEPER-366.patch
>
>
> the leader tracks session expirations by calculating when a session will
> timeout and then periodically checking to see what needs to be timed out
> based on the current time. this works great as long as the leaders clock
> progresses at a steady pace. the problem comes when there are big (session
> size) changes in clock, by ntp for example. if time gets adjusted forward,
> all the sessions could timeout immediately. if time goes backward sessions
> that should timeout may take a lot longer to actually expire.
> this is really just a leader issue. the easiest way to deal with this is to
> have the leader relinquish leadership if it detects a big jump forward in
> time. when a new leader gets elected, it will recalculate timeouts of active
> sessions.
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