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From "Benjamin Reed (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ZOOKEEPER-313) Problem with successive leader failures when no client is connected
Date Fri, 13 Feb 2009 22:51:00 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-313?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12673409#action_12673409
] 

Benjamin Reed commented on ZOOKEEPER-313:
-----------------------------------------

excellent find! thanx for the test case too! you are correct the new leader transaction is
not being logged but should be. (actually according to our design spec, it must be.)

> Problem with successive leader failures when no client is connected 
> --------------------------------------------------------------------
>
>                 Key: ZOOKEEPER-313
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-313
>             Project: Zookeeper
>          Issue Type: Bug
>          Components: server
>    Affects Versions: 3.0.0, 3.0.1
>         Environment: all
>            Reporter: Sunanda Bera
>             Fix For: 3.1.1
>
>
> Steps to reproduce:
> Create a 3 node cluster . Run some transactions and then stop all clients. Make sure
no other clients connect for the duration of the test.
> Let L1 be the current leader. Bring down L1. Let L2 be the leader chosen.  Let the third
node be N3. Note that this will increase the txn id for N3's snapshot without any  transaction
being logged. Now bring up L1 -- same will happen for L1. Now bring down L2.
> Both N3 and L1 now have snapshots with a transaction id greater than the last logged
transaction. Whoever is elected leader will try to restore its state from the filesystem and
fail.
> One easy workaround is obviously to change the FileTxnSnapLog not to save a snapshot
if zxid > last logged zxid. The correct solution is possibly to log a transaction for leader
election as well.

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