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https://issues.apache.org/jira/browse/ZOOKEEPER-3947?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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anaud updated ZOOKEEPER-3947:
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Description: It is possible that there is a follower, which is the old
leader, with a transaction only it saw as the single entry in the log file from
the last epoch. The follower tries to sync with the new leader. It gets TRUNC
request, but in the truncate method of FileTxnLog.java, the FileTxnIterator
will fast-forward to the log file containing the sole transaction. Also, the
pos is pointing to the sole transaction, which is actually the target to
truncate. Therefore, doing a setLength(pos) does not discard this transaction.
The itr.goToNextLog() is not true in this case if the log file was the last
one. Consequently, the transaction remains in the followers log and gets
applied to the in-memory data tree of the follower. Therefore, convergence
fails.
> truncate in FileTxnLog.java is buggy and fails to correctly truncate a file
> containing a single transaction only the follower saw
> ---------------------------------------------------------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-3947
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3947
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.7.0
> Reporter: anaud
> Priority: Major
>
> It is possible that there is a follower, which is the old leader, with a
> transaction only it saw as the single entry in the log file from the last
> epoch. The follower tries to sync with the new leader. It gets TRUNC request,
> but in the truncate method of FileTxnLog.java, the FileTxnIterator will
> fast-forward to the log file containing the sole transaction. Also, the pos
> is pointing to the sole transaction, which is actually the target to
> truncate. Therefore, doing a setLength(pos) does not discard this
> transaction. The itr.goToNextLog() is not true in this case if the log file
> was the last one. Consequently, the transaction remains in the followers log
> and gets applied to the in-memory data tree of the follower. Therefore,
> convergence fails.
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