ZooKeeperServer not starting on leader due to a race condition
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Key: ZOOKEEPER-1144
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1144
Project: ZooKeeper
Issue Type: Bug
Affects Versions: 3.4.0
Reporter: Vishal Kher
Priority: Blocker
Fix For: 3.4.0
I have found one problem that is causing QuorumPeerMainTest:testQuorum to fail.
This test uses 2 ZK servers.
The test is failing because leader is not starting ZooKeeperServer after leader
election. so everything halts.
With the new changes, the server is now started in Leader.processAck() which is
called from LeaderHandler. processAck() starts ZooKeeperServer if majority have
acked NEWLEADER. The leader puts its ack in the the ackSet in Leader.lead().
Since processAck() is called from LearnerHandler it can happen that the
learner's ack is processed before the leader is able to put its ack in the
ackSet. When LearnerHandler invokes processAck(), the ackSet for
newLeaderProposal will not have quorum (in this case 2). As a result, the
ZooKeeperServer is never started on the Leader.
The leader needs to ensure that its ack is put in ackSet before starting
LearnerCnxAcceptor or invoke processAck() itself after adding to ackSet. I
haven't had time to go through the ZAB2 changes so I am not too familiar with
the code. Can Ben/Flavio fix this?
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