Nicholas Wolchko created ZOOKEEPER-2418:
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Summary: txnlog diff sync can skip sending some transactions to
followers
Key: ZOOKEEPER-2418
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2418
Project: ZooKeeper
Issue Type: Bug
Components: server
Affects Versions: 3.5.1
Reporter: Nicholas Wolchko
Priority: Critical
If the leader is having disk issues so that its on disk txnlog is behind the in
memory commit log, it will send a DIFF that is missing the transactions in
between the two.
Example:
There are 5 hosts in the cluster. 1 is the leader. 5 is disconnected.
We commit up to zxid 1000.
At zxid 450, the leader's disk stalls, but we still commit transactions because
2,3,4 are up and acking writes.
At zxid 1000, the txnlog on the leader has 1-450 and the commit log has
500-1000.
Then host 5 regains its connection to the cluster and syncs with the leader. It
will receive a DIFF containing zxids 1-450 and 500-1000.
This is because queueCommittedProposals in the LearnerHandler just queues
everything within its zxid range. It doesn't give an error if there is a gap
between peerLastZxid and the iterator it is queueing from.
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