Distributed transactions with container-managed MDBs

Question

          I have built a framework that employs a high rate of code reuse while abstracting
          the complexities of inter-application communication. This allows application
          developers to focus on solving their business needs and not worry about "the plumbing"
          between the applications.
          At this point, the framework is using container-managed MDBs for Topic destinations.
          MDBs were chosen because of their concurrent nature for processing JMS messages.
          Now that I have this framework up and running, I am trying to add distributed
          transaction support and am having trouble understanding what I need to do. Here
          is how the framework works:
          The MDB will recieve a message, unmarshall it into a business object, and then
          route that object to the appropriate business class where it is then processed
          accordingly. In most cases, the processing of this message object will require
          database interaction. If any error should occur while processing the message,
          all XAResources within the transaction should rollback and ultimately, the JMS
          message will be redelivered later.
          Here is what I'm trying to find out:
          1. When control is passed to an application and it gets a DB connection, will
          that DB resource be dynamically enlisted with the transaction?
          2. Must the DB connection come from the WLS DB pool to be enlisted with the transaction?
          I ask this because the current standard at this company is to use a home-grown
          DB connection pool for getting DB connections. This is due to the fact that not
          all applications here run in a WLS environment and they wanted a standard way
          of retrieving a DB connection across applications. They also sited problems with
          WLS 4.5.1 connection pool.
          3. The documentation states that only one database may be involved in a transaction.
          If a connection to another database is required, but not needed in the current
          transaction, will WLS ignore enlisting the 2nd DB resource, or throw an exception?
          4. Where can I find <B>detailed</B> information about this subject? Everything
          that I have read so far has barely scratched the surface for this specific topic.
          Thanks,
          Bob.
          

Answer 1

          Hi Bob,
          If you are using WLS's XA connection pool, then the XAResource associated with
          the XA connections are enlisted with the transaction transparently for you. Enlistments
          actually occur not at getConnection, but on demand when the JDBC objects are actually
          used.
          If you are not using WLS connection pools, then you would need to enlist the XAResource
          associated with the XA connections yourself. You can obtain the transaction associated
          with the current thread by calling weblogic.transaction.TxHelper.getTransaction(),
          and then call enlistResource on the transaction.
          Weblogic has provisions that allow one (and only one) non-XA connection pool to
          participate in a distributed transaction. In this case, you will get a SQLException
          when you try to obtain a connection from a second connection pool in the same
          distributed transaction. However, if you are using real XA connection pools,
          there is no limitation and any number of XA connection pools can participate in
          the same distributed transaction.
          We will try to incorporate more info in our online docs in the future.
          -- Priscilla Fung, BEA Systems, Inc.
          "Bob Peroutka" <[email protected]> wrote:
          >
          >I have built a framework that employs a high rate of code reuse while
          >abstracting
          >the complexities of inter-application communication. This allows application
          >developers to focus on solving their business needs and not worry about
          >"the plumbing"
          >between the applications.
          >
          >At this point, the framework is using container-managed MDBs for Topic
          >destinations.
          > MDBs were chosen because of their concurrent nature for processing JMS
          >messages.
          >
          >Now that I have this framework up and running, I am trying to add distributed
          >transaction support and am having trouble understanding what I need to
          >do. Here
          >is how the framework works:
          >
          >The MDB will recieve a message, unmarshall it into a business object,
          >and then
          >route that object to the appropriate business class where it is then
          >processed
          >accordingly. In most cases, the processing of this message object will
          >require
          >database interaction. If any error should occur while processing the
          >message,
          >all XAResources within the transaction should rollback and ultimately,
          >the JMS
          >message will be redelivered later.
          >
          >Here is what I'm trying to find out:
          >
          >1. When control is passed to an application and it gets a DB connection,
          >will
          >that DB resource be dynamically enlisted with the transaction?
          >
          >2. Must the DB connection come from the WLS DB pool to be enlisted with
          >the transaction?
          >
          >I ask this because the current standard at this company is to use a home-grown
          >DB connection pool for getting DB connections. This is due to the fact
          >that not
          >all applications here run in a WLS environment and they wanted a standard
          >way
          >of retrieving a DB connection across applications. They also sited problems
          >with
          >WLS 4.5.1 connection pool.
          >
          >3. The documentation states that only one database may be involved in
          >a transaction.
          > If a connection to another database is required, but not needed in the
          >current
          >transaction, will WLS ignore enlisting the 2nd DB resource, or throw
          >an exception?
          >
          >4. Where can I find <B>detailed</B> information about this subject?
          > Everything
          >that I have read so far has barely scratched the surface for this specific
          >topic.
          >
          >Thanks,
          >
          >Bob.