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From "Tellier Benoit (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAILBOX-209) A data race is possible with Cassandra modseq generation
Date Wed, 21 Jan 2015 09:00:55 GMT
Tellier Benoit created MAILBOX-209:
--------------------------------------

             Summary: 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


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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