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https://issues.apache.org/jira/browse/CASSANDRA-17162?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17445914#comment-17445914
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Unmesh Joshi commented on CASSANDRA-17162:
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Consider following scenario
Alice, Bob and Mary are trying to set their names on servers A, B and C.
Alice tries to propose name=Alice at timestamp ballot 100
A promises with in-progress-ballot 100
B promises in-progress-ballot 100
C is not reached
Alice gets majority promises
A is not reachable and goes in a retry loop.
B is not reachable and goes in a retry loop.
C is not reachable and goes in a retry loop.
Bob tries to propose name=Bob at timestamp ballot 200
A promises with in-progress-ballot 200
B promises with in-progress-ballot 200
C is not reachable.
Bob gets majority of promises
A is not reachable
B accepts proposal 200, Bob. proposal-ballot set to 200.
C accepts proposal 200, Bob, proposal-ballot set to 200
Alice's retries work
A rejects proposal because in-progress-ballot is set to 200.
B is not reachable.
C accepts proposal 100, Alice. proposal-ballot set to 100. (overwriting value
Bob, because Bob's acceptance did not set in-progress-ballot).
Mary tries a proposal at timestamp ballot 300
A promises with in-progress-ballot set to 300
B is unreachable
C promises with in-progress-ballot set to 300 and returns proposal-ballot 100
and value Alice.
Mary gets majority promises for ballot 300 and chooses value Alice.
A accepts proposal 300 with value Alice
B accepts proposal 300 with value Alice
C accepts proposal 300 with value Alice
So unless the proposal sets and checks in-progress ballot, the values can
potentially be overwritten with delayed proposals?
Or am i missing something in this scenario?
> In the paxos implementation, a delayed proposal might overwrite newer values
> ----------------------------------------------------------------------------
>
> Key: CASSANDRA-17162
> URL: https://issues.apache.org/jira/browse/CASSANDRA-17162
> Project: Cassandra
> Issue Type: Bug
> Reporter: Unmesh Joshi
> Priority: Normal
> Attachments: paxos-fix.patch
>
>
> I was going through this blog post , which talks about a possible bug in
> paxos implementation if in-progress ballot is not set while accepting a
> proposal.
> [https://brooker.co.za/blog/2021/11/16/paxos.html]
> I tried writing a failing test and possible fix.
> The in_progress_ballot needs to be set when accepting a proposal. The current
> implementation sets only the proposal_ballot when accepting a proposal.
>
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