Including or excluding loaded tables from WAITFORDATA queries

The WAITFORDATA option has been designed to add Hybrid Transactional Analytical Processing (HTAP) capabilities to the product. It minimizes the problem of replication latency for incrementally updated tables. However, a query might reference incrementally updated tables as well as tables that have not been enabled for incremental updates (loaded tables that can be referenced by accelerated queries).

About this task

If you set the WAITFORDATA option to a value greater than 0.0, loaded accelerator-shadow tables tables and accelerator-only tables referenced by a query would, without further intervention, be waiting for incremental updates that never happen. The expiration period would always expire, and the query would fail because this is what happens when updates cannot be applied within the expiration period. It is therefore important that loaded tables can be included in queries with a WAITFORDATA setting. That is, after the passing of the specified WAITFORDATA delay, queries can go against a set of incrementally updated tables, a mixed set of tables, and even against a set of loaded tables only.

By default, loaded tables are excluded because there is a greater probability of data inconsistency. You can change this behavior and include loaded tables. This is recommended if you know that queries go against a mixed set of tables.

For a more detailed description of the WAITFORDATA option, follow the link to Making queries wait for incremental updates at the end of this topic.

Procedure

Log on to the IBM Db2 Analytics Accelerator Console.

Press the Pause key, then Enter to display the following screen:

*****************************************************************************
*         Welcome to the IBM Db2 Analytics Accelerator Configuration Console
*****************************************************************************

You have the following options:
 (0) - (Menu) Manage Configuration Console Users                                                
 (1) - (Menu) Run Accelerator Functions
 (2) - (Menu) Manage Incremental Updates 
 (3) - (Menu) Manage Encryption of Data in Motion
 (4) - (Menu) Manage Call Home
                                                                             
 ----------------------------------------------------------------------         
 (x) - Exit the Configuration Console

Type 2 and press Enter to display the submenu:

 main -> 2                                               
 --------------------------------------------------------
 You have the following options:                         
                                                         
(0) - Go back one level                
(1) - Enable incremental updates       
(2) - Disable incremental updates      
(3) - Restart incremental update processes
(4) - Include or exclude tables not enabled for incremental updates 
      in WAITFORDATA queries
(5) - Allow or disallow queries to run if WAITFORDATA timeout is reached
(6) - Change Db2 for z/OS credentials for Integrated Synchronization
(7) - Change IP and secure DDF port of Db2 for z/OS for Integrated Synchronization
(8) - (Menu) Manage certificates for replication
(9) - Integrated Synchronization status

(Default 0) >

Type 4 and press Enter.

The following screen is displayed:

Specify if tables that were loaded, but not enabled for 
incremental updates, are to be included in delayed queries 
(queries running with a setting of WAITFORDATA > 0.0).

It cannot be guaranteed that the data in these accelerator-shadow 
tables is up-to-date. If changes have been made to a Db2 source table, 
a new load process must be started to propagate these changes to the 
accelerator. Only then will these changes be reflected in the result set of
accelerated queries.

The current setting is: 'Included'

Do you want to include loaded tables in WAITFORDATA queries? 
('yes', 'no', or <return> to cancel): <cursor>

To change the value from no to yes or vice versa, type n or y at the prompt (position of <cursor> in the screen extract). Then press Enter.
To exit the dialog without changes, just press Enter.
After a change or confirmation of the present value, you see the following message:
```
Done. The new setting is now active and will be used with the next query 
that is offloaded to the accelerator.
```
Press Enter again to return to the submenu.

What to do next

To change your settings, repeat steps 4 through 6. Specify a different value in step 5.