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From "Tellier Benoit (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAILBOX-209) A data race is possible with Cassandra modseq generation
Date Fri, 13 Mar 2015 15:46:38 GMT

    [ https://issues.apache.org/jira/browse/MAILBOX-209?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14360525#comment-14360525

Tellier Benoit commented on MAILBOX-209:

See MAILBOX-208.

> A data race is possible with Cassandra modseq generation
> --------------------------------------------------------
>                 Key: MAILBOX-209
>                 URL: https://issues.apache.org/jira/browse/MAILBOX-209
>             Project: James Mailbox
>          Issue Type: Bug
>            Reporter: Tellier Benoit
>         Attachments: MAILBOX-209-rebased.patch, fix_cassandra_modseq_provider.patch
> The Cassandra mailbox implementation proceed as follow to increase the modseq :
>  - a first call to Cassandra to increase the modseq value for a given mailbox
>  - a second call allow us to retrieve the current value.
> Note that you can not do it in a single call...
> In a distributed environment, imagine that :
>  - for a mailbox the current modseq is n
>  - server A increments modseq. Modseq is n+1
>  - server B increments modseq. Modseq is n+2
>  - server A and B then retrieve the modseq value and have a duplicated modseq : they
for instance both can assign n+2 value to a different message.
> The problem can be solved using conditionnal updates with lightweight transactions.

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