[ https://issues.apache.org/jira/browse/CASSANDRA-6013?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Jeremy Hanna updated CASSANDRA-6013: ------------------------------------ Labels: LWT (was: ) > CAS may return false but still commit the insert > ------------------------------------------------ > > Key: CASSANDRA-6013 > URL: https://issues.apache.org/jira/browse/CASSANDRA-6013 > Project: Cassandra > Issue Type: Bug > Reporter: Sylvain Lebresne > Assignee: Jonathan Ellis > Priority: Major > Labels: LWT > Fix For: 2.0.1 > > Attachments: 6013-v2.txt, 6013-v3.txt, 6013-v4.patch, 6013.txt > > > If a Paxos proposer proposes some value/update and that propose fail, there > is no guarantee on whether this value will be accepted or not ultimately. > Paxos guarantees that we'll agree on "a" value (for a given round in our > case), but does not guarantee that the proposer of the agreed upon value will > know it. In particular, if for a given proposal at least one accepter has > accepted it but not a quorum does, then that value might (but that's not > guaranteed either) be replayed (and committed) by another proposer. > Currently, if a proposer A proposes some update U but it is rejected, A will > sleep a bit and retry U. But if U was accepted by at least one acceptor, some > other proposer B might replay U, succeed and commit it. If A does its retry > after that happens, he will prepare, check the condition, and probably find > that the conditions don't apply anymore since U has been committed already. > It will thus return false, even though U has been in fact committed. > Unfortunately I'm not sure there is an easy way for a proposer whose propose > fails to know if the update will prevail or not eventually. Which mean the > only acceptable solution I can see would be to return to the user "I don't > know" (through some exception for instance). Which is annoying because having > a proposal rejected won't be an extremely rare occurrence, even with > relatively light contention, and returning "I don't know" often is a bit > unfriendly. -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org