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From "sankalp kohli (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6246) EPaxos
Date Tue, 30 Sep 2014 00:22:34 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6246?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14152592#comment-14152592
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sankalp kohli commented on CASSANDRA-6246:
------------------------------------------

Inconsistencies can be introduced by machines being down or network partitioned for longer
than we replay missed updates to it. Currently for normal writes, hint is for 1 hour. If you
bring in a machine after 1 hour, you run a repair. But repair won't help here since it takes
time to run the repair and new LWTs will come and will see a different view of the data and
won't apply. 

"However, like I mentioned in my comment yesterday, I think we can work out a way to detect
and correct this."
+1

"Assuming each instance is an average of ~170 bytes (uncompressed), sustained 1000 instances
per second for 3 hours would keep ~1.8GB of data around."
Here instance includes the condition and update. Update could be quite big and keeping it
around could be problematic. 



> EPaxos
> ------
>
>                 Key: CASSANDRA-6246
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6246
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Blake Eggleston
>            Priority: Minor
>
> One reason we haven't optimized our Paxos implementation with Multi-paxos is that Multi-paxos
requires leader election and hence, a period of unavailability when the leader dies.
> EPaxos is a Paxos variant that requires (1) less messages than multi-paxos, (2) is particularly
useful across multiple datacenters, and (3) allows any node to act as coordinator: http://sigops.org/sosp/sosp13/papers/p358-moraru.pdf
> However, there is substantial additional complexity involved if we choose to implement
it.



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