Qlik Replicate DB2i Source Endpoint Performance setting for Apply Change Task

[Bill_Steinagle]

This article covers how to improve performance when using the Qlik Replicate Source Endpoint DB2i in a task, specifically by enabling the AfterImageOnly Internal Parameter.

Enabling the AfterImageOnly option on a DB2 for i (DB2i) source endpoint in Qlik Replicate provides performance and efficiency benefits, particularly when running Apply Changes tasks.

Content

• What is AfterImageOnly?
• Setting AfterImageOnly
• What are the benefits of enabling AfterImageOnly?
• When not to use AfterImageOnly

What is AfterImageOnly?

In DB2i journaling, every change to a record can be logged with:

• Before image: the state of the record before the change.
• After image: the state of the record after the change.

By default, both images may be captured. The AfterImageOnly setting signals Qlik Replicate to capture only the after image of each change.

Setting AfterImageOnly

AfterImageOnly is an Internal Parameter. To set it:

1. Go to the DB2i Source Endpoint 
2. Open the Advanced tab
3. Scroll to the bottom and click Internal Parameters
   
   
   
   
4. Add the Internal Parameter AfterImageOnly and tick the Value checkbox
   
   
   
   
5. Save your changes
   
   

No reload of the task or table is required. You can resume your task after saving the Endpoint.

What are the benefits of enabling AfterImageOnly?

1. Reduced CPU Usage on iSeries
   • Processing only the after image reduces the workload on the DB2i system.
   • Less data needs to be read, parsed, and transferred.
2. Lower Latency
   • Smaller journal entries lead to faster reads and quicker replication cycles.
   • Especially helpful when multiple tasks are reading from the same journal.
3. Lower Network Bandwidth Usage
   • Only the necessary data (the new state of the record) is transferred.
   • This is particularly useful in high-volume environments.
4. Simpler Change Processing
   • For Apply Changes tasks, only the after image is typically needed.
   • This simplifies the logic and speeds up the apply process on the target.
5. Cleaner Journal Reads
   • Reduces the volume of journal entries that need to be scanned and interpreted.
   • Helps avoid bottlenecks when multiple tasks are reading from the same journal receiver.

When not to use AfterImageOnly

AfterImageOnly does not fit every situation. To not use the parameter, if:

• You do full auditing, conflict detection, or custom transformations that require the before image
• You use Upsert or Merge logic that relies on comparing old vs. new values

Environment

• Qlik Replicate