[jira] Commented: (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:comment-tabpanel&focusedCommentId=12900511#action_12900511 ] 

Benjamin Reed commented on ZOOKEEPER-366:
-----------------------------------------

after discussion this on the list, we realized that we can detect a big jump in time change in the session expiration thread. since we expire a bucket of sessions each tick, if we run into the situation where we are going to expire more than one bucket in a row, we know we have jumped forward in time. we can "smooth" the jump by requiring at least a 1/2 ticktime wait between each bucket. 

> 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
>
> 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.

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.