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List: james-dev
Subject: [jira] [Created] (MAILBOX-209) A data race is possible with Cassandra modseq generation
From: "Tellier Benoit (JIRA)" <jira () apache ! org>
Date: 2015-01-21 9:00:55
Message-ID: JIRA.12768927.1421830809000.132602.1421830855312 () Atlassian ! JIRA
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Tellier Benoit created MAILBOX-209:
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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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