[jira] Updated: (ZOOKEEPER-366) Session timeout detection can go wrong if the leader system time changes

["Benjamin Reed (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-366?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

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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