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https://issues.apache.org/jira/browse/CURATOR-460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16416588#comment-16416588
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Antonio Rafael Rodrigues commented on CURATOR-460:
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1) I think the timeAtSuspendedEvent you are talking about is the one hold by
clientCnxnSocket#getIdleRecv() in the class ClientCnxn.java of ZK code, that
call returns the time of last interaction with the server, but as far as I
understand the code, we don't have access to the clientCnxnSocket from Curator.
So we don't know for sure the elapsed time.
Even if Curator had access to getIdleRecv() I don't think if would be very
useful, as after Zookeeper realizes that it has passed 2/3 of the
sessionTimeout without heard from server, it enqueues the error and resets the
time counter, by calling clientCnxnSocket.updateLastSendAndHeard()
As you said, there is also the possibility of start the Curator's timer already
in 2/3 of sessionTimeout. By the way, it already can be achieved by using
SessionConnectionStateErrorPolicy and setting
StandardConnectionHandlingPolicy.setSimulatedSessionExpirationPercent(*35*)
2)There is already a way to treat SUSPENDED or LOST as the same thing, just use
StandardConnectionStateErrorPolicy.
To sum up:
1) I can be wrong, but looking at the code, there is no way to know the real
elapsed time without changing zookeeper ( I hope someone check that )
2) We can start the counter already in 2/3 of session timeout, even though
there is already a way to do it by configuration.
> Timed tolerance for connection suspended leads to simultaneous leaders
> ----------------------------------------------------------------------
>
> Key: CURATOR-460
> URL: https://issues.apache.org/jira/browse/CURATOR-460
> Project: Apache Curator
> Issue Type: Bug
> Components: Recipes
> Affects Versions: 3.3.0, 4.0.0, 4.0.1
> Reporter: Antonio Rafael Rodrigues
> Assignee: Cameron McKenzie
> Priority: Major
>
> Starting from Curator 3, after losing the connection to zookeeper, curator
> emits a SUSPENDED event and then starts an internal timer, if the time of the
> negotiatied session timeout get hit and curator didn't reconnect to zookeeper
> it emits a LOST event.
> For example :
> Given negotiated session timeout = 40
> ||Time (seconds)||Event||
> |0|SUSPENDED (curator has been disconnected from zookeeper)|
> |40|LOST (curator is still disconnected, it must have been lost the sesion as
> it is disconnected for 40sec)|
> Given this scenario we could ,theoretically, ignore the SUSPENDED event and
> consider the leadership as lost just if the ConnectionStateListener receives
> the LOST event.
> But this feature seems to have introduced a bug (from my point of view)
> *Case of failure*
> ||Time (seconds)||Event||
> |0|Something went wrong with the connected zookeeper (in my case, the network
> inteface of zookeeper's server has gone down). Curator stops hearing heart
> beats from zookeeper, but doesn't lose the connection (from some reason that
> I don't know, if the network interface of the server goes down, Curator
> doesn't lose the connection)|
> |~26.666|SUSPENDED (after 26 seconds without hearing heartbeats, curator
> emits a SUSPENDED event) 26 is from "readTimeout = sessionTimeout * 2 / 3"
> from the class ClientCnxn.java from zookeeper client. At this point, curator
> starts counting 40 sec.|
> |26.666 to 40|During this period, Curator is trying to connect to other
> zookeeper instances but the other instances, in my example case, are also
> uncheachable.|
> |40|Session has expired and the other instance has taken leadership ( in my
> example, the other instance can connect to zookeeper )|
> |66.666|LOST ( after 40sec from SUSPENDED, curator finally sends LOST)|
> As you can see, if we are ignoring the SUSPENDED event, the second
> application instance acquires the leadership ~26 seconds before the first
> instance notice that it lost the leadership.
> I understand it seems to be a very rare case, but either way I think it
> should be addressed.
> *Reproduce it*
> I have came up with a way to reproduce this easily. I know this is not a
> recommended production setup, but it reproduces the problem anyway.
> 1) On a virtual machine, with 2 network interfaces (eth0[192.168.0.101],
> eth1[192.168.0.102]) , I installed one zookeeper instance.
> 2) I setup application1 with the leadership receipe, with 40sec of
> negotiated timeout, pointing just to 192.168.0.101 .Now it is the leader
> 3) I setup application2 with the leadership receipe, with 40sec of
> negotiated timeout, pointing just to 192.168.0.102 .Now it it is NOT the
> leader
> 4) On the server I turn the eth0[192.168.0.101] interface down [ ifconfig
> eth0 down ]
> 5) After 26 seconds, application1 says :
> :ClientCnxn$SendThread@1111] - Client session timed out, have not
> heard from server in 26679ms for sessionid
> ConnectionStateManager@237] - State change: SUSPENDED
> NOTE: I'm ignoring the SUSPENDED event
> 6) After 40 seconds, application2 takes leadership
> 7) After 66 seconds, application1 says :
> ConnectionStateManager@237] - State change: LOST
>
> NOTE: Just at this point, I consider that the application1 has lost
> leadership
> Then, for 26 seconds, we had 2 leaders.
> If you confirm it as a bug, I think I could help.
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