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From "Norbert Pfistner (JIRA)" <j...@apache.org>
Subject [jira] Created: (AMQ-2184) Messages keep hanging in JDBCStore without delivery to client
Date Thu, 26 Mar 2009 14:13:43 GMT
Messages keep hanging in JDBCStore without delivery to client
-------------------------------------------------------------

                 Key: AMQ-2184
                 URL: https://issues.apache.org/activemq/browse/AMQ-2184
             Project: ActiveMQ
          Issue Type: Bug
          Components: Broker
    Affects Versions: 5.2.0, 5.1.0
         Environment: OS: Linux version 2.6.26-amd64-85 (root@etch64) (gcc version 4.1.2 20061115
(prerelease) (Debian 4.1.1-21))
ActiveMQ: 5.1.0
1 Broker, 12 JBoss's  with round about 20 consumers and  20 Producers on 7 JDBC persistant
queues
Clients use transacted consumers.
            Reporter: Norbert Pfistner
            Priority: Blocker
             Fix For: 5.3.0


We currently suffer from hanging messages in the JDBC persistant storage in our production
environment. 

Occasionally (once in a day or week) a few Messages (most time 1 or 2, sometimes more) seems
to stuck in the DB Table activemq_msg without being delivered even once to a consumer. They
are never deliverd to a consumer until the broker is rebooted. Strange enough new messages
produced into the same queue with those stuck messages are delivered to the consumers as normal.
It simply looks like the borker is blind about the stuck messages.

Our system depends on processing every message, so missing even one of them is realy a big
problem in production.

Everything seems to be fine: No warnings, errors or even debug logging gives any hint about
a problem. 
Unfortunately we can't debug the broker 'cuse it's our production environment. Our Testing
envirenment is not capable to reproduce the problem (actually it's only one Machine with a
Broker and a signle jaboss running a small number of producers/clients).

Our messaging characteristics show  moderate producers and slow consumers. The count of simultanous
messages is moderate (about 300-1000). Actually the producers have hot phases generating bulks
of Messages followed by phases of long inactivity. The consumers are slow related to the producers
but always keep within an hour or two. We do not experience any memory problems.



Because this bug may be related to https://issues.apache.org/activemq/browse/AMQ-1918, I had
a look at the code around the StoreCursors and stumbled apon a strange code fragment called
when removing entries.

The suspicous code is found in org.apache.activemq.broker.region.cursors.AbstractStoreCursor.remove()
in 5.1.0, 5.2 .0 and 5.3.0:

    public final synchronized void remove() {
        size--;
        if (size==0 && isStarted() && cacheEnabled) {
            cacheEnabled=true;
        }
    }

As far as i can see, the if statement ist actually a NOP, 'cause it will not modify cacheEnabled
in any case.

Maybe this causes some strange effects when using the StoreCursor's derived from this class..





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