A blocking transformation withholds output until it has received and processed every input row. Downstream components cannot begin until processing finishes. section 6.3.2
Recognize the distinction:
- Non-blocking transformations, such as Derived Column, output processed batches as soon as they are ready. section 6.3.2
- Aggregate is blocking because grouped totals or averages cannot be confirmed until no more rows can change them. section 6.3.2
Grouped campaign averages
An Aggregate transformation calculates average BidPrice and CostPerMille for each unique CampaignID, CountryCode, and EventTime combination. It must receive all rows before releasing those averages. section 6.3.2
