Qlik Replicate: What does Reload Target do on a CDC only task?

[KellyHobson]

In this article, we will explain what occurs when you stop a CDC only task and issue a Run > Reload Target.  This will initiate the task in 'fresh start mode' and begin processing changes from that point in time.  Thus, if a task stops processing changes at 2:00 AM and you issue a reload target at 7:00 AM, you will lose 5 hours' worth of changes.  

For the scenario above, this is where the Advanced run -> restart from time or SCN comes in handy. 

Example

1. Start a task with Full load and CDC enabled with one table to be replicated.
   
   
   
   In the log we see:
   
   00008248: 2023-03-07T20:11:42 [TASK_MANAGER ]I: Task 'mysql_baddate' running full load and CDC in fresh start mode (replicationtask.c:1767)
   
   The full load completes, and all records are there. Now we are running in CDC mode.
   
   
   
   
2. Test an insert on source table:
   
   INSERT INTO kelly.Persons2 VALUES(37,'rita','2010-11-01 05:00:00');
   
   Insert completes and shows in target table.
   
   
   
   
3. Let's say I update the task to run CDC only. Stop the task, open task settings, disable Full load, save changes.
   
   
   
   Make another insert on the source table:
   
   INSERT INTO kelly.Persons2 VALUES(38,'John','2010-11-01 05:00:00');
   
   Task is resumed.
   
   00009936: 2023-03-07T20:26:22 [TASK_MANAGER ]I: Task 'mysql_baddate' running CDC only in resume mode (replicationtask.c:1767)
   
   Change is picked up successfully on the resume.
   
   
   
   
   
   
4. Let's say I stop the task again and make a change on source.
   
   INSERT INTO kelly.Persons2 VALUES(39,'Jimmy','2010-11-01 05:00:00');
   
   Then do a Run > Reload Target
   
   00009868: 2023-03-07T20:28:26 [TASK_MANAGER ]I: Task 'mysql_baddate' running CDC only in fresh start mode (replicationtask.c:1767)
   
   This switches the task to fresh start mode and will not pick up most recent record (Jimmy).
   
   Only after the fresh start is initiated will it start processing changes.
   
   Make an insert on the source table:
   
   INSERT INTO kelly.Persons2 VALUES(40,'Jessie','2010-11-01 05:00:00');
   
   

Conclusion

A Run > Reload on CDC only task is not the same as a 'Reload' for a Full load task. It will only begin processing changes from that point in time when the fresh start mode was initiated.

If your CDC only task experiences an outage or an issue with the source, you need to have steps in place to run an Advanced run > Restart from Time/or SCN.

Environment

• Qlik Replicate 

The information in this article is provided as-is and to be used at own discretion. Depending on tool(s) used, customization(s), and/or other factors ongoing support on the solution below may not be provided by Qlik Support.