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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2678) Large databases take a long time to regain a quorum
Date Thu, 09 Feb 2017 19:25:41 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2678?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15860031#comment-15860031
] 

ASF GitHub Bot commented on ZOOKEEPER-2678:
-------------------------------------------

Github user hanm commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/159#discussion_r100389617
  
    --- Diff: src/java/main/org/apache/zookeeper/server/quorum/Learner.java ---
    @@ -498,14 +504,19 @@ else if (qp.getType() == Leader.SNAP) {
                                throw new Exception("changes proposed in reconfig");
                            }
                         }
    -                    if (!snapshotTaken) { // true for the pre v1.0 case
    -                       zk.takeSnapshot();
    +                    if (isPreZAB1_0) {
    +                        zk.takeSnapshot();
                             self.setCurrentEpoch(newEpoch);
                         }
                         self.setZooKeeperServer(zk);
                         self.adminServer.setZooKeeperServer(zk);
                         break outerLoop;
    -                case Leader.NEWLEADER: // it will be NEWLEADER in v1.0        
    +                case Leader.NEWLEADER: // Getting NEWLEADER here instead of in discovery

    +                    // means this is Zab 1.0
    +                    // Create updatingEpoch file and remove it after current
    --- End diff --
    
    This comment does not apply here - my guess is it is a copy paste error from your branch-3.4
patch... can we get this comment removed?


> Large databases take a long time to regain a quorum
> ---------------------------------------------------
>
>                 Key: ZOOKEEPER-2678
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2678
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: server
>    Affects Versions: 3.4.9, 3.5.2
>            Reporter: Robert Joseph Evans
>            Assignee: Robert Joseph Evans
>
> I know this is long but please here me out.
> I recently inherited a massive zookeeper ensemble.  The snapshot is 3.4 GB on disk. 
Because of its massive size we have been running into a number of issues. There are lots of
problems that we hope to fix with tuning GC etc, but the big one right now that is blocking
us making a lot of progress on the rest of them is that when we lose a quorum because the
leader left, for what ever reason, it can take well over 5 mins for a new quorum to be established.
 So we cannot tune the leader without risking downtime.
> We traced down where the time was being spent and found that each server was clearing
the database so it would be read back in again before leader election even started.  Then
as part of the sync phase each server will write out a snapshot to checkpoint the progress
it made as part of the sync.
> I will be putting up a patch shortly with some proposed changes in it.



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