Problem with successive leader failures when no client is connected 

                 Key: ZOOKEEPER-313
             Project: Zookeeper
          Issue Type: Bug
          Components: server
    Affects Versions: 3.0.1, 3.0.0
         Environment: all
            Reporter: Sunanda Bera

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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