Qlik Replicate - Hash based compare

[narashan]

Wanted to confirm if Qlik Replicate uses hashing algorithm and comparison to check for changes to a data element/record to identify a CDC/update? 

This is important especially when there are LOBs in the table that gets updated and the hash check would degrade performance.  

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Thank you PadmaPriya...want to make sure that the question is clear:

We have a database (DB2) that has CLOB elements with JSON data. We have enabled CDC from the DB2 instance to S3. The question is to confirm  and understand how Qlik recognises a change to this CLOB. For e.g., there is an update to a specific record and the JSON in the CLOB is the only element updated, but there was no change to the JSON it was identical to the previous one...

So will Qlik recognise that 1) There was an update, 2) only one column was updated, 3) do a hash compare to ensure that the value has changed, 4) if the JSONs are identical before and after update then the hash values would be same, 5) Qlik will not trigger an update CDC for this record since nothing changes, 6) If Qlik is not doing a data compare on update then after step #2 above it will just replicate the record with operation code "Update"

[PadmaPriya]

Hello @narashan 

Please refer to below articles:

https://help.qlik.com/en-US/replicate/November2020-SR1/Content/Global_Common/Content/SharedEMReplica...

https://www.qlik.com/us/products/qlik-replicate

https://community.qlik.com/t5/QlikView-App-Dev/Key-field-generation-methods-comparison/td-p/1410504

Thanks,

Padma Priya

[narashan]

Thank you...want to make sure that the question is clear:

We have a database (DB2) that has CLOB elements with JSON data. We have enabled CDC from the DB2 instance to S3. The question is to confirm  and understand how Qlik recognises a change to this CLOB. For e.g., there is an update to a specific record and the JSON in the CLOB is the only element updated, but there was no change to the JSON it was identical to the previous one...

So will Qlik recognise that 1) There was an update, 2) only one column was updated, 3) do a hash compare to ensure that the value has changed, 4) if the JSONs are identical before and after update then the hash values would be same, 5) Qlik will not trigger an update CDC for this record since nothing changes, 6) If Qlik is not doing a data compare on update then after step #2 above it will just replicate the record with operation code "Update"