Incremental updates

The incremental update function of IBM Db2 Analytics Accelerator for z/OS® allows you to update accelerator-shadow tables continually. Changes to the data in original Db2 for z/OS tables are thus propagated to the corresponding target tables with a high frequency and just a brief delay. This way, query results from an accelerator are always extracted from recent, close-to-real-time data.

If you followed the instructions in this guide, you already installed the necessary IBM InfoSphere® Change Data Capture for z/OS (CDC) components by completing the steps in Installing libraries with IBM Db2 Analytics Accelerator for z/OS support. However, for updates or more detailed information, follow the link to the installation instructions in the IBM InfoSphere Change Data Capture for z/OS information center at the end of this topic.

Attention:
  • It is not possible to integrate and use an existing CDC installation. You must use a dedicated CDC that was installed from the SMP/E installation package delivered with IBM Db2 Analytics Accelerator for z/OS.
  • A risk of data loss exists if you include tables without a unique constraint, such as a primary key or a unique index. To identify rows in such a table, the values of all table columns are used. It is possible that rows with exactly the same values exist, in which case it is impossible to identify a row unambiguously. Hence a deletion of a single row from a table in Db2 for z/OS results in the deletion of this row and all its duplicates from the corresponding accelerator-shadow table. This, in turn, leads to incorrect results for accelerated queries.
  • If you update Db2 for z/OS tables by running the LOAD utility rather than an INSERT, UPDATE, or DELETE operation, you must set the following parameters (for the LOAD utility):
    • SHRLEVEL CHANGE
    • LOG YES
    Otherwise, the changes that were made by the LOAD utility are not detected by the incremental update function, and will thus not be reflected in your accelerator-shadow tables.
  • With the introduction of IBM Db2 Analytics Accelerator for z/OS Version 3.1, the Db2 attribute DATA CAPTURE is added to the tables on an accelerator. The attribute can carry the value Y or N (default), for yes or no. When incremental updates are enabled for a table, the DATA CAPTURE attribute of the table is set to the value Y. Once set, this attribute value persists, even if the table is disabled at a later time. Bear this in mind, especially if you run applications that use the DATA CAPTURE attribute.
  • You might have to reload or even remove tables from an accelerator after the execution of an ALTER TABLE or ALTER TABLESPACE statement in Db2 for z/OS. For more information, see What to do after changing a table or table space in Db2 for z/OS. You find a Related reference link at the end of this topic.
Restriction: It is not possible to enable tables if the table name or the schema name contains GB18030 characters (Simplified Chinese) of Unicode plane 2 (U+20000-U+2FFFF: Supplementary Ideographic Plane). Trying to do so results in an error.