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Posted to issues@zookeeper.apache.org by "Michael Han (JIRA)" <ji...@apache.org> on 2019/08/02 04:12:00 UTC
[jira] [Assigned] (ZOOKEEPER-3485) Measure reconfiguration time
[ https://issues.apache.org/jira/browse/ZOOKEEPER-3485?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Michael Han reassigned ZOOKEEPER-3485:
--------------------------------------
Assignee: Karolos Antoniadis
> Measure reconfiguration time
> ----------------------------
>
> Key: ZOOKEEPER-3485
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3485
> Project: ZooKeeper
> Issue Type: Improvement
> Affects Versions: 3.5.5
> Reporter: Karolos Antoniadis
> Assignee: Karolos Antoniadis
> Priority: Minor
>
> This issue is created after some initial discussion in the _dev_ mailing list (subject "Leader election logging during reconfiguration").
>
> There does not seem to be a good way to measure reconfiguration time in ZooKeeper. Additionally, reconfiguration time is mixed together with leader election time*.* For instance, during reconfiguration, ZooKeeper logs a {{LEADER ELECTION TOOK}} message even though no leader election might takes place.
>
> This can be reproduced by following these steps:
> 1) start a ZooKeeper cluster (e.g., 3 participants)
> 2) start a client that connects to some follower
> 3) perform a _reconfig_ operation that removes the leader from the cluster
>
> After the reconfiguration takes place, we can see that the log files of the remaining participants contain a "_LEADER ELECTION TOOK_" message. For example, a line that contains
> _2019-07-29 23:07:38,518 [myid:2] - INFO [QuorumPeer[myid=2](plain=0.0.0.0:2792)(secure=disabled):Follower@75] - FOLLOWING - LEADER ELECTION TOOK - 57 MS_
>
> However, no leader election took place, in the sense that no server went _LOOKING_ and then started voting and sending notifications to other participants as would be in a normal leader election. It seems, that before the _reconfig_ is committed, the participant that is going to be the next leader is already decided (see here: [https://github.com/apache/zookeeper/blob/master/zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/Leader.java#L865]).
>
> *Goal* of this issue/improvement is to measure in a better and more accurate way the time it takes for a reconfiguration to complete, as well as, to clearly distinguish the measurement of reconfiguration versus leader election.
>
>
>
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