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Improving Log Master performance

Log Master requires information from the following types of Db2 data sets, in addition to the logs:
  • Image copies

  • Bootstrap data sets (BSDS)

  • Table space data sets

  • Repository tables

  • Several catalog tables

To enable Log Master to execute with the greatest efficiency, observe the following practices (listed in order of highest to lowest importance):

  1. Do not delete records from SYSIBM.SYSCOPY (using the MODIFY utility) or the BSDS (using the DSNJU003 utility) until the records are older than any archive logs that are to be scanned. For example, if you need to scan a log that is one month old, Log Master requires the log, image copies, and SYSCOPY information for one month. If the SYSCOPY information is missing,Log Master cannot perform row completion processing (acquiring complete before and after images of a row update record). Decompression processing might fail if you are not using DATA CAPTURE CHANGES and KEEPDICTIONARY. If BSDS information is missing for archive logs, Log Master cannot access those archive logs.

  2. Use DATA CAPTURE CHANGES for the tables of interest for Log Master processing. If you use DATA CAPTURE NONE, for Log Master to provide any output that contains detailed column data, such as SQL, LOAD, logical log, and detailed reports, Log Master might be required to perform multiple log scans across various ranges, and read image copy data sets. By altering on DATA CAPTURE CHANGES, you can avoid the overhead of row completion processing for partially logged updates.

    Note

    DDL generation always induces completion processing for LOB spaces that are associated with the catalog.

  3. Keep image copies on DASD until they are no longer required for Log Master processing. Reading tape data sets can be time consuming. If multiple image copies are stacked on tape, Log Master attempts to optimize for completion processing, but not for compression dictionary acquisition.

  4. Regularly run REPOS UPDATE with INCLUDE DICTIONARY to store the following types of information in the Repository:

    • Table schema information (used for DROP RECOVERY processing)

    • Compression dictionaries (used to avoid image copy processing)

      For more information, see REPOS UPDATE.

  5. Regularly run REPOS DELETE to purge obsolete data from the Log Master Repository. For more information, see REPOS DELETE.

  6. If Log Master reloads compression dictionaries during processing (see messages BMC097677I at the end of ALPPRINT) and a DICTIONARYSPACE value is specified in the OPTION command, delete that value to increase the dictionary space allocation. For details, see DICTIONARYSPACE.

  7. In a data sharing environment, if Db2 processing for your tables of interest occurs only on a small subset of the data sharing members, use the OPTION statement, USELGRNG YES syntax option (USELGRNG) to avoid scanning the logs of all members of the data sharing group. Consider experimenting with this option if you are unsure about the nature of the Db2 processing.

  8. (PTF BQU1717 applied) Regularly run REPOS UPDATE INCLUDE SYSCOPY to store SYSIBM.SYSCOPY records. This is especially important before performing maintenance on a table space, such as using a utility to modify the SYSCOPY records.



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