Michael Han created ZOOKEEPER-2833:
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Summary: Keep the follower transaction up to date after the fix
made in ZOOKEEPER-2355.
Key: ZOOKEEPER-2833
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2833
Project: ZooKeeper
Issue Type: Improvement
Components: quorum, server
Affects Versions: 3.5.3, 3.5.2, 3.5.1, 3.5.0, 3.4.10, 3.4.9, 3.4.8
Reporter: Michael Han
Assignee: Michael Han
After the fix did in ZOOKEEPER-2355, the follower's transaction log might not
be up to date, because with the fix in this patch, we will never do
setlastProcessedZxid during a DIFF sync. For example imagine a case like this:
* Follower has its latest zxid with value a before DIFF SYNC happens.
* Leader send over proposals with zxids value b, c, d.
* Follower received and applied proposals b and c. Before follower had a chance
to get hands on d, network partition happens.
* Now partition healed, follower will do a DIFF think again. Because the zk
database would not be reloaded from logs (it's already initialized), follower
has a skewed view of the world - it thinks it only has tnx a, but in fact it
has a, b, and c. So rather asking b, c, and d, the follower could just ask d.
We should also set the zxid extracted from the current proposal packet after
each proposal is committed. It is not functional critical and is an
optimization because the idempotent nature of applying transactions.
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