Support net changes

[pasquij]

1. When enabling CDC on a table, when do we want to set support_net_changes to 0? My understanding is that we want to set this to 1 to optimize Qlik replication. Is my understanding correct? Are there cases where we want to set this to 0 for optimization purposes?

The only use case I can think of for setting support_net_changes to 0 is when there is a process in ODS (e.g. trigger or ETL process or an audit) that needs to account every transaction that is coming in. is my understanding correct?

2. We turned on 'Store Changes Processing' in the Qlik tasks. If we set support_net_changes to 1, will that have any impact on the contents of the CT tables in target database? Or will the CT tables always contain each and every transaction done on the OLTP?

[SachinB]

Hello @pasquij ,

Thank you for reaching out to Qlik community !

When using RDS SQL Source, there is a requirement to enable CDC in the Database and in the Tables: 

 
To enable CDC in the Database: 

exec msdb.dbo.rds_cdc_enable_db 'db_name'  

 
To enable CDC for a single table: 

exec sys.sp_cdc_enable_table _schema = N'db_name', _name = N'table_name', @role_name = NULL, @supports_net_changes = 1 GO 

 
Hope you are looking this option for source as AMAZON RDS for SQL as source.

https://help.qlik.com/en-US/replicate/November2023/Content/Replicate/Main/AWS%20RDS%20MSSQL/aws_set_...

If yes, you can find the more information on below article.

https://community.qlik.com/t5/Official-Support-Articles/RDS-SQL-Source/ta-p/1740676

Regards,

Sachin B

[pasquij]

Hi @SachinB 

We are using Microsoft SQL Server as a  source.

My assumption is that it is better to set support_net_changes to 1 to optimize Qlik replication. Is this correct?

For example, if we insert a  record and then update the record in source, we will want to replicate the net change to target. Instead of replicating both insert and update in target, we want to insert the latest form of the record in target. Given this, we want to set  support_net_changes to 1 (If  support_net_changes is set to 0, then we will always have to do both insert and update in target).

Is my understanding correct? 

Are there cases where we want to set  support_net_changes to 0?

Thanks,

[SachinB]

Hello @pasquij ,

Our user guide does not specify about this, when you are using as MS SQL Server as source endpoint. But its highlighted in AMAZON RDS SQL server as source endpoint.

I would advise you to create Support case in order to check with internal team and will advise you accordingly 

Thanks for understanding. 

Regards,

Sachin B

[pasquij]

Hi @SachinB 

I read this documentation: Change Processing Tuning #Change Processing Tuning | Qlik Replicate Help

For 'Batch optimized apply' change processing mode, is it required to set @supports_net_changes = 1 when enabling CDC on a table?