[ https://issues.apache.org/jira/browse/CURATOR-460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16433873#comment-16433873 ]
ASF GitHub Bot commented on CURATOR-460: ---------------------------------------- Github user Randgalt commented on the issue: https://github.com/apache/curator/pull/262 Yeah, I agree @cammckenzie. Let's merge what we have here and I'll write up a Tech Note. > 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 > Attachments: ConnectionStateManager.patch, > Console-leaderSelector1.log, Console-leaderSelector2.log, > CuratorLeaderSelectorPOC.java, LogApp1.log, LogApp2.log > > > 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. -- This message was sent by Atlassian JIRA (v7.6.3#76005)