VMS Help  —  RMU72  Unload  Database  Command Qualifiers, Compression
    Compression[=options]
    NoCompression

    Data compression is applied to the user data unloaded to the
    internal (interchange) format file. Table rows, null byte vector
    and LIST OF BYTE VARYING data are compressed using either the LZW
    (Lempel-Ziv-Welch) technique or the ZLIB algorithm developed by
    Jean-loup Gailly and Mark Adler. Table metadata (column names and
    attributes) are never compressed and the resulting file remains
    a structured interchange file. Allowing compression allows the
    result data file to be more compact, using less disk space and
    permitting faster transmission over communication lines. This
    file can also be processed using the RMU Dump Export command.

    The default value is Nocompression.

    This qualifier accepts the following optional keywords (ZLIB is
    the default if no compression algorithm is specified):

    o  LZW

       Selects the LZW compression technique.

    o  ZLIB

       Selects the ZLIB compression technique. This can be modified
       using the LEVEL option.

    o  LEVEL=number

       ZLIB allows further tuning with the LEVEL option that accepts
       a numeric level between 1 and 9. The default of 6 is usually
       a good trade off between result file size and the CPU cost of
       the compression.

    o  EXCLUDE_LIST[=(column-name,...)]

       It is possible that data in LIST OF BYTE VARYING columns is
       already in a compressed format (for instance images as JPG
       data) and therefore need not be compressed by RMU Unload.
       In fact, compression in such cases might actually cause
       the output to grow. The EXCLUDE_LIST option will disable
       compression for LIST OF BYTE VARYING columns. Specific column
       names can be listed, or if omitted, all LIST OF BYTE VARYING
       columns will be excluded from compression.

    Only the user data is compressed. Therefore, additional
    compression may be applied using various third party compression
    tools, such as ZIP. It is not the goal of RMU to replace such
    tools.

    The qualifier RECORD_DEFINITION (or RMS_RECORD_DEF) is not
    compatible /COMPRESSION. Note that the TRIM option for DELIMITED
    format output can be used to trim trailing spaces from VARCHAR
    data.
Close Help