3 Replies Latest reply on Nov 28, 2005 8:08 AM by Oystein Aadland

    Memory problems starting JBossmq with DB2

    Oystein Aadland Newbie

      Hi

      I have an application running on JBoss 3.2.7 using the JBossmq the comes with the installation of JBoss. We've been running this over half a year with almost no problems (At least not releated to JBoss code).

      A short time ago however, we had trouble starting the JBoss instance again after a planned down period. After searching for the cause we found the problem to be related to loading for messages from a JMS destination. When trying to load the messages DB2 threw an exception complaining about out of memory (APP_CTL_HEAP_SZ set to low). In the JBossmq code the messages are loded with this sql:

      SELECT MESSAGEID, MESSAGEBLOB FROM JMS_MESSAGES WHERE MESSAGEID=? AND DESTINATION=?


      The loading code is located in the loadFromStorage method in org.jboss.mq.pm.jdbc2.PersistenceManager

      We checked out how many messages could be loaded this way with the default setting of DB2. The anwere where 1600 messages. So if there are more messages in a single destination then the mq service wouldn't start.

      We have discussed this with IBM support and they are telling us that DB2 works as designed. According to them the heap is cleared when the transaction commits. In my opinion this is pretty stupid since you cannot navigate backwards in the recordset, and already read rows could be garbagecollected at once.

      The interesting thing here is that there isn't any memory problems at the applicationserver, but only in DB2. Adjusting the APP_CTL_HEAP_SZ to higher levels cannot solve our problem since it doesn't scale well.

      My questions are:

      Have anyone else had similar problems either with DB2 or other databases?
      Do anyone have a solution to how to get around this?

      A rather simple solution (I think) for us would be to modify the loading code i JBossmq to load fewer messages in one transaction, and repeat until all messages are loaded. But we would prefere not to do this unless this is accepted into the JBossmq code.

      Thank you.
      Oystein Aadland

      PS: I tried to search for similar posts in the forum and the bug database without finding anything. If I missed it I apologise for the inconvenience.