How does CDC work with IBM DB2 for iSeries as a source?

[iti-attunity-sup]

I have two questions:

1. How dose QR check for data changes that occur in DB2? For example, in Oracle, I believe you check for SCN increments.

2. After detecting data changes, I assume QR read the journal. How dose QR load the journal at this time?
For instance, QR read the entire portion since the last read in time, or split it into multiple reads, etc.?

[iti-attunity-sup]

Hello Desmond

Thanks for reply.

You mentioned "Replicate will check again after 5 seconds." Is QSYS2.Display_Journal() the method used for this check?

What I want to know is, if the method for reading the journal is different from the method for checking whether there are changes in the journal, could you explain how the check is performed?

best regards.

[john_wang]

Hello @iti-attunity-sup ,

Qlik Replicate calls the API once, and will process all the available changes in the journal, until to the end of the journal. Then Qlik Replicate will sleep, and startup the processing again after the Check for changes every (sec) expires.

thanks,

John.

[iti-attunity-sup]

Hello John

Thanks for reply.

In other words, am I correct in understanding that Qlik Replicate does not check if there have been any updates to the journal?

best regards.

[john_wang]

Hello @iti-attunity-sup ,

Seems I did not get your doubt accurately. Could you please elaborate the scenario?

Regards,

John.

[iti-attunity-sup]

Hello John

Based on our previous exchanges, I understand the following:

• Qlik Replicate calls the QSYS2.Display_Journal() API to read the journal.
• The portion of the journal to be read is controlled by the STARTING_SEQUENCE parameter.
• While Qlik Replicate is reading the journal, if changes continue to be recorded in the journal, it will continue to read until it reaches the end.
• After reading to the end of the journal, the next time Qlik Replicate calls the QSYS2.Display_Journal() API, it sets the value of the STARTING_SEQUENCE parameter to the next position from the last read point.

Is my understanding the same as yours so far?

What I want to know is whether Qlik Replicate, after sleeping for the period specified by "Check for changes every (sec)", checks if there have been updates in the journal and calls the QSYS2.Display_Journal() API only if there are updates, or if it calls the API without performing a check.

best regards.

[john_wang · Accepted solution]

Hi @iti-attunity-sup ,

There is not special 'pre-check' step to detect if new changes coming, only the API is called: return changes, or nothing.

Regards,

John.