Compressing DEDBs

Use the following procedure to compress a DEDB:

  1. (optional) Run the Trial utility.You can run the Trial utility to preview the effects of compression on database segments. By analyzing the reports produced, you can determine the technique that produces the highest compression.

    This step is required if you want to build a new Shared Table or Custom Hardware Dictionary. After running the Trial utility, you must promote the table or dictionary from STAGE level to RUN level, then promote the associated segment registration records from STAGE level to RUN level, before continuing to Step 2.

  2. (optional) Create DPICDS entries.DPICDS entries contain information about the compression technique to be used and any other DATA PACKER/IMS options you select. These entries can be created online or in batch. Entries are not required if you choose to use all the DATA PACKER/IMS standard defaults, including Static Huffman compression.

  3. Create a test DBD.Copy your current DBD to a test library, and modify the SEGM statement to add the appropriate compression parameters as shown in the following example. The INIT parameter is required for DATA PACKER/IMS.

     COMPRTN=(DPIFPRTN,DATA,INIT)

    You may need to modify your DEDB unit of work (UOW) root parameter to reclaim space before reloading your database. If you reduce the UOW, you must perform an IMS cold start after the ACBGEN. For help in determining the optimal parameter values, you can use the Area Change Modeling Utility that is available BMC Fast Path Analyzer/EP product. For more information, see the supporting utilities information in the Fast Path/EP Series Reference Manual.

  4. Generate the new DBD.
  5. Perform an ACBGEN for the test DBD that you created.
  6. (optional) Modify the space allocations.Reclaim the space freed by DATA PACKER/IMS by modifying your database’s space allocation.

  7. (optional) Change the database. 

    Note

    This step is necessary only if you want to compress all of your data. Because DATA PACKER/IMS recognizes uncompressed data, you do not have to change the entire database; you can change one area at a time.

    If you have a license for the BMC Fast Path Reorg/EP product, you can make the database change with an image copy as input. For additional information, see the Fast Path Offline Suite User Guide. Refer to the CHANGE command and the EXPAND=YES keyword, which are necessary to invoke DATA PACKER/IMS compression.

    If you use DEDB Unload/Reload Utility component of the IBM Fast Path Basic Tools for OS/390, the database change is a two-stage step:

    1. Unload the database. Use both the OLDACB DD and the NEWACB DD statements pointing to the appropriate libraries.
    2. Reload the database. Specify the COMPRESS=NO control statement. For additional information, see the IBM IMS Fast Path Basic Tools for OS/390 Users Guide.

 

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