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  1. #1
    Join Date
    Oct 2010

    Unanswered: Impact of CDC on OLTP throughput

    We are moving off the Mainframe for a couple of our OLTPs to AIX - the backend is still on DB2.

    The problem: Our EDW loads extracted only changed data through IBM's Log Analyzer tool on the Mainframe. Now that this is going to AIX, we will need a CDC mechanism of some kind in the distributed world -

    Options I am aware of are -

    1. SQL Rep (Free with Db2 LUW, right?) - not very fast? and Only DB2 replication possible
    2. Qrep - Licensing purchase - fast and DB2 and Oracle replication

    All this is good, however, the OLTP stakeholders are pushing back saying they have a performance concern around the CDC reading the transaction log. I am not given numbers to substantiate this. My understanding is that CDC is an industry best-practice and there would have to be a strong argument against not performing CDC - performance is a genuine concern for OLTPs but would need to established.

    Obvious question:
    In you guys' experience, have you ever seen significant performance problems from conventional CDC ? If so, what was done to remediate?

    As always, THANKS FOR YOUR HELP!

    - G
    Last edited by getback0; 04-20-11 at 13:42.

  2. #2
    Join Date
    Jun 2003
    Toronto, Canada
    Provided Answers: 1
    There is a separate product - IBM InfoSphere Change Data Capture, formerly known as DataMirror, - so don't confuse the three.

    It's not clear from your description whether your OLTP systems are the source or the target of replication; I'm assuming the former.

    Since SQL replication Capture reads transaction data from the logs that have already been written, I don't see how that can affect OLTP workload (unless, of course, your system is running at close to 100% of CPU and/or I/O capacity, in which case you have bigger problems to solve). You can schedule Capture so as to minimize interference with other workloads.

  3. #3
    Join Date
    Oct 2010
    Thanks for the confirmation n_i! The OLTP is the source for replication.

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