Why model-level aggregations do not reduce gateway traffic for Import mode

PL-300 By islever Editorial Last updated

Transform and load the data

Short answer

B No, model-level aggregations reduce query work, not the detail volume crossing the gateway during Import refresh.

Question

Note: This question is part of a series of questions that present the same scenario. Each question in the series contains a unique solution that might meet the stated goals. Some question sets might have more than one correct solution, while others might not have a correct solution. After you answer a question in this section, you will NOT be able to return to it. As a result, these questions will not appear in the review screen. You have an on-premises data gateway. You need to reduce the amount of data sent through the gateway by semantic models that run in Import storage mode. Solution: You create aggregations to summarize results. Does this meet the goal?
  1. Yes
  2. No Correct Answer

Key Takeaways

User-defined aggregations live in the semantic model and reduce query-time work, not refresh-time transfer — the full detail still flows through the gateway on every import refresh, so the traffic is not reduced.

An on-premises data gateway carries full Import refresh data, and the proposed fix of creating aggregations to summarize results is evaluated against the goal of reducing the volume sent through the gateway.

Common mistake: Conflating query-side aggregation with transfer-side reduction — aggregations make visuals faster against the model but do nothing about how many bytes cross the gateway during the scheduled import refresh.

Expert Analysis

Why the Answer Is Correct

Aggregations as described in Power BI are summary tables and relationships built inside the semantic model (the aggregations feature in Manage aggregations). They accelerate DirectQuery-style queries and reduce what the engine must compute at query time, but every import refresh still pulls the complete detail rows from the on-premises source across the gateway. Because the goal is specifically to reduce the amount of data sent through the gateway by Import-mode models, and refresh traffic is unchanged, the solution does not meet the goal.

Why the Other Options Are Wrong

Answering Yes would be valid only if the aggregation were performed in the source query itself — for example grouping in Power Query with query folding so the source sends pre-summarized rows. The solution as stated does not say the summarization is pushed to the source; in Power BI terminology 'create aggregations' denotes the model-level feature, and that leaves gateway transfer untouched. A model that imports less data requires source-side filtering or aggregation, which this solution never claims.

Community Comment Notes

The most-endorsed comment explains the crux: aggregations summarize after the data has already come through the gateway, so traffic is not reduced. A reply adds the useful nuance that the answer would flip to Yes if the aggregation were done at the source, confirming the No verdict for the solution as worded.

Official Reference

https://learn.microsoft.com/en-us/power-bi/transform-model/desktop-aggregations

This link opens the official vendor documentation in a new tab.

Exam Strategy

Distinguish between model-level aggregations and source-side transformations when asked about reducing gateway traffic. Model-level 'aggregations' only speed up queries; they do not change the volume of data imported. To reduce gateway load, look for solutions involving source filtering, query folding, or incremental refresh.

Frequently Asked Questions

Do Power BI aggregations reduce on-premises gateway traffic?

No, model-level aggregations summarize data after it has already been transferred through the gateway during refresh.

How to reduce data sent through the Power BI gateway in Import mode?

Apply filters or aggregations at the source using query folding in Power Query so less data is pulled into the model.

More PL-300 FAQ →

Community Votes

B
61%
A
39%

61% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 10 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 10

  1. 1CY1 👍 7 Answered B
    Create aggregations to summarize results. This seems to be saying group and summarize after the data has come through the gateway as an import. This will not reduce the traffic as it has already come through the gateway. Answer : B.No.
  2. chicken_chaser 👍 4 Answered B
    depends on where the aggregation is conducted. If it is done in power BI then the amount of data will still be the same. If the aggregation is done in the source then Yes
  3. tko86 👍 3 Answered B
    It can't be B. If the data is imported and you then you aggregate (creating summarize tables) off the imported data, you are not reducing the overall model. You are actually increasing the size. While the summarize table would perform quicker, the original imported table with all the data remains. You need to reduce it at it's source before you bring in the data through import storage.
  4. Odidepse 👍 3 Answered A
    Yes, creating aggregations to summarize results reduces the amount of data sent through the on-premises data gateway by summarizing the data in the semantic model. Creating aggregation reduce querying time and compression.
  5. jaume 👍 3 Answered A
    Aggregations allow you to precompute and store summarized data, which minimizes the need to load and query large amounts of detailed data. This approach is particularly beneficial in large DirectQuery or Import models:
Show 5 more comments
  1. amiruladliroslibin 👍 3
    not sure of question. you aggregate the results after importing? then the answer is no. if you are doing it before then the answer is yes
  2. lmml_et 👍 2 Answered A
    You create aggregations in Power Query before importing data, soy you reduce de amount of data in the semantic model and in the gateway
  3. Pey1nkh 👍 1 Answered A
    creating aggregations reduces the amount of data sent through the gateway and optimizes data refresh and query performance.
  4. ec338ed 👍 1
    answer is yes. Aggregating ans summarizing reduces data.
  5. LuluSkyy 👍 2
    The answer is A.

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