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https://issues.apache.org/jira/browse/ZOOKEEPER-1697?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13653229#comment-13653229
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Flavio Junqueira commented on ZOOKEEPER-1697:
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Hi Pat, The new approach you propose looks good to me. One advantage is that it
concentrates the changes on LearnerHandler and it is easier to read the code
this way.
I like the approach of resetting tickOfLastAck for the second ack and on
because the first ack is a bit odd, so resetting is a way of separating the
timing of the first ack from the rest.
In your patch, I was actually thinking that this statement:
{code}
tickOfNextAckDeadline = leader.self.tick + leader.self.initLimit;
{code}
might not be right because of the following argument. An instance of
LearnerHandler may take up to initLimit to get to the point that the leader is
running. From the point that the LearnerHandler instance crosses the start up
while loop, we should grant another syncLimit ticks until next ack because the
first might have arrived right before it crosses the while loop, no? If so,
then perhaps the initialization of tickOfNextAckDeadline should be instead:
{code}
tickOfNextAckDeadline = leader.self.syncLimit + leader.self.initLimit;
{code}
Let me know what you think.
> large snapshots can cause continuous quorum failure
> ---------------------------------------------------
>
> Key: ZOOKEEPER-1697
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1697
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.4.3, 3.5.0
> Reporter: Patrick Hunt
> Assignee: Patrick Hunt
> Priority: Critical
> Fix For: 3.5.0, 3.4.6
>
> Attachments: ZOOKEEPER-1697_branch34.patch,
> ZOOKEEPER-1697_branch34.patch, ZOOKEEPER-1697.patch, ZOOKEEPER-1697.patch
>
>
> I keep seeing this on the leader:
> 2013-04-30 01:18:39,754 INFO
> org.apache.zookeeper.server.quorum.Leader: Shutdown called
> java.lang.Exception: shutdown Leader! reason: Only 0 followers, need 2
> at org.apache.zookeeper.server.quorum.Leader.shutdown(Leader.java:447)
> at org.apache.zookeeper.server.quorum.Leader.lead(Leader.java:422)
> at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:753)
> The followers are downloading the snapshot when this happens, and are
> trying to do their first ACK to the leader, the ack fails with broken
> pipe.
> In this case the snapshots are large and the config has increased the
> initLimit. syncLimit is small - 10 or so with ticktime of 2000. Note
> this is 3.4.3 with ZOOKEEPER-1521 applied.
> I originally speculated that
> https://issues.apache.org/jira/browse/ZOOKEEPER-1521 might be related.
> I thought I might have broken something for this environment. That
> doesn't look to be the case.
> As it looks now it seems that 1521 didn't go far enough. The leader
> verifies that all followers have ACK'd to the leader within the last
> "syncLimit" time period. This runs all the time in the background on
> the leader to identify the case where a follower drops. In this case
> the followers take so long to load the snapshot that this check fails
> the very first time, as a result the leader drops (not enough ack'd
> followers w/in the sync limit) and re-election happens. This repeats
> forever. (the above error)
> this is the call:
> org.apache.zookeeper.server.quorum.LearnerHandler.synced() that's at
> odds.
> look at setting of tickOfLastAck in
> org.apache.zookeeper.server.quorum.LearnerHandler.run()
> It's not set until the follower first acks - in this case I can see
> that the followers are not getting to the ack prior to the leader
> shutting down due to the error log above.
> It seems that sync() should probably use the init limit until the
> first ack comes in from the follower. I also see that while tickOfLastAck and
> leader.self.tick is shared btw two threads there is no synchronization of the
> shared resources.
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