VMS Help  —  RMU72  Unload  After Journal, Command Qualifiers, Continuous
    Continuous
    Nocontinuous

    Causes the LogMiner process to attach to the database and begin
    extracting records in "near-real" time. When the Continuous
    qualifier is specified, the RMU Unload After_Journal command
    extracts records from the online after-image journal files of the
    database until it is stopped via an external source (for example,
    Ctrl/y, STOP/ID, $FORCEX, or database shutdown).

    A database must be explicitly enabled for the Continuous LogMiner
    feature. To enable the Continuous LogMiner feature, use the RMU
    Set Logminer command with the Enable and Continuous qualifiers;
    to disable use of the Continuous LogMiner feature, use the RMU
    Set Logminer command with the Enable and Nocontinuous qualifiers.

    The output from the Continuous LogMiner process is a continuous
    stream of information. The intended use of the Continuous
    LogMiner feature is to write the changes into an OpenVMS
    mailbox or pipe, or to call a user-supplied callback routine.
    Writing output to a disk file is completely functional with the
    Continuous LogMiner feature, however, no built-in functionality
    exists to prevent the files from growing indefinitely.

    It is important that the callback routine or processing of
    the mailbox be very responsive. If the user-supplied callback
    routine blocks, or if the mailbox is not being read fast enough
    and fills, the RMU Unload After_Journal command will stall. The
    Continuous LogMiner process prevents backing up the after-image
    journal that it is currently extracting along with all subsequent
    journals. If the Continuous LogMiner process is blocked from
    executing for long enough, it is possible that all available
    journals will fill and will not be backed up.

    When a database is enabled for the Continuous LogMiner feature,
    an AIJ "High Water" lock (AIJHWM) is utilized to help coordinate
    and maintain the current .aij end-of-file location. The lock
    value block for the AIJHWM lock contains the location of the
    highest written .aij block. The RMU Unload After_Journal command
    with the Continuous qualifier polls the AIJHWM lock to determine
    if data has been written to the .aij file and to find the highest
    written block. If a database is not enabled for the Continuous
    LogMiner feature, there is no change in locking behavior; the
    AIJHWM lock is not maintained and thus the Continuous qualifier
    of the RMU Unload After_Journal command is not allowed.

    In order to maintain the .aij end-of-file location lock,
    processes that write to the after-image journal file must use
    the lock to serialize writing to the journal. When the Continuous
    LogMiner feature is not enabled, processes instead coordinate
    allocating space in the after-image journal file and can write
    to the file without holding a lock. The Continuous LogMiner
    process requires that the AIJHWM lock be held during the .aij
    I/O operation. In some cases, this can reduce overall throughput
    to the .aij file as it serves to reduce multiple over-lapped I/O
    write operations by multiple processes.

    The Save_Metadata and Restore_Metadata qualifiers are
    incompatible with the Continuous qualifier.
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