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List:       james-dev
Subject:    [jira] [Updated] (MAILBOX-209) A data race is possible with Cassandra modseq generation
From:       "Tellier Benoit (JIRA)" <jira () apache ! org>
Date:       2015-01-21 9:05:34
Message-ID: JIRA.12768927.1421830809000.132629.1421831134738 () Atlassian ! JIRA
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     [ https://issues.apache.org/jira/browse/MAILBOX-209?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel \
]

Tellier Benoit updated MAILBOX-209:
-----------------------------------
    Attachment: fix_cassandra_modseq_provider.patch

In this patch, we first get the current modseq value. We increase it only if the \
value did not change. If it is the case, we can then return the incremented value. If \
it is not the case, we just retry.

Note a tunnable max retry parameter ( to avoid being stuck )

To validate all cassandra unit tests ( mailbox mappers espacially ), it has to behave \
well even if the mailbox does not exist. Hence the separated table.

> 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: 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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