⚡ Dataflows Gen2 in Microsoft Fabric: From “Dataslows” to Fast
Dataflows have always been the “least performant” option in Microsoft Fabric for data ingestion. That’s changing rapidly with two new features: Modern Evaluator and Partitioned Compute.
🔧 What are Dataflows Gen2?
They are Fabric’s no-code/low-code ETL tool (extract, transform, and load data). With 100+ built-in connectors, they use the familiar Power Query interface and store output as Delta tables in OneLake — without writing a single line of code.
📊 How big is the improvement? (real data: 29 million rows / 2.5 GB):
| Mode | Seconds | CUs consumed |
|---|---|---|
| Dataflow Gen1 | 550s | 7,788 CUs |
| Gen2 no optimizations | 520s | 5,684 CUs |
| Gen2 + Modern Evaluator | 368s | 3,565 CUs ✅ |
| Gen2 + Modern Evaluator + Partitioned | 474s | 4,732 CUs |
With Modern Evaluator enabled, consumption drops to less than 50% compared to Dataflow Gen1.
🔍 Explanation in a nutshell
In Microsoft Fabric, a Capacity Unit (CU) is the billing unit: how much CPU, memory, and I/O an operation uses. Previously, every second of Dataflow execution cost 16 CUs; the new engine reduces this dramatically. The Modern Evaluator runs on .NET 8 for faster query execution, and Partitioned Compute processes parts of the transformation logic in parallel instead of sequentially.
More information at the link 👇
