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SQL Server change tracking

In this article

    The Online customer database uses SQL Server change tracking to manage all tables that are subject to mirroring.

    SQL Server change tracking is a light-weight mechanism implemented directly in the SQL Server database engine. It uses an incremental 64-bit integer, Log Sequence Number.

    Using this method, rather than the internal TravelTransactionLog, avoids complexity in the following situations:

    • UDEF changes
    • Merging 2 companies is logged differently from other operations
    • Service operations are not logged at all in TravelTransactionLog

    How does it work?

    1. When change tracking for a table is OFF, it is automatically turned ON by the mirroring system.
    2. A  wipe message is sent to the client.
    3. All records in the table are considered changed and therefore transmitted to the client.

    How long is tracking data kept?

    Change tracking data is kept for 7 days.

    If a mirroring client service is down for more than a week, change data will be missing and the next synctronization will therefore cause a complete, automatic repopulation of the mirror.