Jiafu Jiang created ZOOKEEPER-3607:
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Summary: Potential data inconsistency due to the inconsistency
between ZKDatabase.committedLog and dataTree in Trunc sync.
Key: ZOOKEEPER-3607
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3607
Project: ZooKeeper
Issue Type: Bug
Components: quorum
Affects Versions: 3.4.14
Reporter: Jiafu Jiang
I will describe the problem by a detail example.
1. Suppose we have three zk servers: zk1, zk2, and zk3. zk1 and zk2 are online,
zk3 is offline, zk1 is the leader.
2. In TRUNC sync, zk1 sends a TRUNC request to zk2, then sends the remaining
proposals in the committedLog. *When the follower zk2 receives the proposals,
it applies them directly into the datatree, but not the committedLog.*
3. After the data sync phase, zk1 may continue to send zk2 more committed
proposals, and they will be applied to both the datatree and the committedLog
of zk2.
4. Then zk1 fails, zk3 restarts successfully, zk2 becomes the leader.
5. The leader zk2 sends a TRUNC request to zk3, then the remaining proposals
from the committedLog. But since some proposals, which are from the leader zk1
in TRUNC sync(as I describe above), are not in the committedLog, they will not
be sent to zk3.
6. Now data inconsistency happens between zk2 and zk3, since some data may
exist in zk2's datatree, but not zk3's datatree.
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