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From "Mahadev konar (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ZOOKEEPER-87) Follower does not shut itself down if its too far behind the leader.
Date Thu, 24 Jul 2008 17:51:31 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-87?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12616550#action_12616550

Mahadev konar commented on ZOOKEEPER-87:

i was thinking abt the same lines but not on maximum capacity on follower handlers -- 

ben and I had a discussion regarding this and we decided on doing htis --- 

1) we send a Leader.PING from the leader to the follower --- we will include the ticktime
at the leader and send it to the follower

2) the follower just returns back the tick time with the ping response. 

3) we update the ticktime that we saw last from the follower and then kill the follower handler
if its lagging behind.

-- this approach is less error prone since we are getting response from the follower and know
whats the last ticktime it processed. The problem with your suggestion is that you might be
sending it out fast to the follower but the follower might be buffering all of it and not
doing anything with it... 

though the above suggestion has a problem right now since the Leader.PING does not go through
the pipeline at the follower. so a response to the ping does not necessarily mean that the
follower is in line with processing the requests. We have to get an end to end response from
the follower to see how much it is behind.. 

> Follower does not shut itself down if its too far behind the leader.
> --------------------------------------------------------------------
>                 Key: ZOOKEEPER-87
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-87
>             Project: Zookeeper
>          Issue Type: Bug
>            Reporter: Mahadev konar
>            Assignee: Mahadev konar
>            Priority: Critical
>             Fix For: 3.0.0
> Currently, the follower if lagging behind keeps sending pings to the leader it will stay
alive and will keep getting further and further behind the leader. The follower should shut
itself down if it is not able to keep up to the leader within some limit so that gurantee
of updates can be made to the clients connected to different servers.

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