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From "Rob Davies (JIRA)" <>
Subject [jira] Resolved: (AMQ-1656) Messages are sometimes skipped when using JDBC master/slave
Date Thu, 10 Apr 2008 17:17:43 GMT


Rob Davies resolved AMQ-1656.

    Resolution: Fixed

Fixed by SVN revision 646880

> Messages are sometimes skipped when  using JDBC master/slave
> ------------------------------------------------------------
>                 Key: AMQ-1656
>                 URL:
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Message Store
>    Affects Versions: 5.0.0
>         Environment: Windows XP sp2, java 6, Mysql 5.0.51a
>            Reporter: Fran├žois Guillemette
>             Fix For: 5.1.0
> Sometime, a (or some) message(s) hang in the queue while no consumer eat it. It happen
more often a failover.
> Scenario:
> 2 brokers (jdbc master/slave), 2 consumers (with prefetch set to 1), 2 producers
> Producers :
>   ant producer -Durl="failover:(tcp://localhost:61618,tcp://localhost:61619)" -Ddurable=true
> Consumer 1:
>   ant consumer -Durl="failover:(tcp://localhost:61618,tcp://localhost:61619)" -Dmax=10000
> Consumer 2:
>   ant consumer -Durl="failover:(tcp://localhost:61618,tcp://localhost:61619)" -Dmax=10000
> 1 - Start the two brokers (one will be master, the other will be slave)
> 2 - Start the producers, consumers
> 3 - Wait a little,
> 4 - Kill the master -> slave become master
> 5 - Producers continue producing, consumers continue consuming
> 6 - After all producers finish their task, the consumer will finish consuming, and sometimes
there still messages left in the queue (in the database, and using JMX to see the state of
the queue).
> 7 - Restart a new broker, kill the master
> 8 - The messages will be consumed 
> There is a race condition between the time the message is set with the broker sequence
number ( in send method), and the time it is actually put in the database
( in doAddMessage method).
> I have seen that sometimes message with higher sequence number are put in database before
a lower sequence number.  For example: 386 is put in the database before 385. If it is happening
when JDBCMessageStore is recovering the next message (lastMessageId is 384), then 386 will
be fetched and the lastMessageId will change to be 386. 385 is then put in the db but never
retrieved (stopping and restarting the broker will allow to retrieve the message because at
start the lastMessageId is -1).
> I have synchronized the code inside the RegionBroker.send, and I don't have gaps anymore.
This is a workaround for us since we don't process a lot of message. But maybe a more elegant
solution is to set the brokerSequenceId in doAddMessage of JDBCAdapter (I may be wrong, I
didn't check if the brokerSequenceId is used elsewhere).

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