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Thread: Reliability, Robustness and Continuity of Attunity CDC

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    Reliability, Robustness and Continuity of Attunity CDC

    Question:
    How do you provide reliability, robustness and continuity in your way of capturing the changed data on iSeries? For example, what if the Attunity Stream is turned off for a few hours, can you assure us that it will continue to process the changed data from the point where it left? If yes can you tell us "how"?
    Answer:

    The answer talks about DB/400 on iSeries but the principle is the same with other CDC sources.

    The Attunity Stream capture process relies on the availability of the iSeries journals so if Attunity Stream was down for 5 hours but the journals are still available on-line then there will be no problem to resume the CDC process. Both system and user managed journals are supported.

    The Attunity Stream system have two main components:

    1. A Capture Agent which is a passive component that reads from a given position in the journal, converting the data read into a common XML-like change record format.
    2. A Change Router which is an active component whose task is to stream captured change events from the agent into a set of change tables. The Change Router deals with cleaning up the change stream from uncommitted changes as well as other concerns (such as allowing referential integrity to be supported in the CDC process). It is the Change Router that keeps the stream position and that can decide when and if to advance it.

    Both components self start following a reboot and both are auto-restarted upon failure.

    Assuming proper setup, the staging area will recover from general errors with no data loss using its recorded stream position to work from the point it stopped processing.

    Note that this process relates to maintaining the staging area with its change tables in a consistent state. Obviously, when the CDC is used as a part of an ETL process, the ETL tool need to ensure it processed all captured changes too. This is facilitated by the use of an incremental stream position field that is part of all change tables.
    Last edited by DrorHarari; 01-24-2007 at 04:50 AM.
    By Dror Harari

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