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Georma's avatar
Georma
New Member
1 month ago
Solved

Why does PBI Service show different Semantic Model storage sizes when VertiPaq memory size is

I'm trying to understand a difference in Semantic Model storage reported by Power BI Service. I have two semantic models: *Both contain approximately 61 million rows. *Both have almost the same ...
General Comment
  • MohamedFowzan1's avatar
    MohamedFowzan1
    1 month ago

    Hi Georma  from what I have seen

    You can inspect things like partitions, model metadata, and object definitions using tabular Editor, but i dont thi k anything takes you perfectly to the system vakue storage. I think microsoft ticket will help with this. Do keep us posted

Gautam_Kumar01's avatar
Gautam_Kumar01
Post Partisan
1 month ago

Hi Georma 

This discrepancy is expected and comes down to what "System Storage" in Power BI Service actually measures vs what VertiPaq Analyzer shows.

 

Short Answer:
VertiPaq Analyzer = Only compressed data in memory
System Storage in Service = VertiPaq data + Everything else in the .pbix/.abf file

 

# What System Storage includes:
1. VertiPaq data - Your 3.64GB / 3.65GB. This matches DAX Studio.
2. Model Metadata - Tables, columns, relationships, measures, roles. Complex models with lots of measures increase this.
3.  L*Power Query M code + Refresh History  - This is the big one for you.
-  Model A (Redshift + PQ transforms : All your Power Query steps, applied steps, and lineage are stored in the model. PQ stores intermediate results and query folding metadata. This can easily add 1-2GB+.
-  Model B (ClickHouse + SQL transforms) : Since transforms are done in SQL, PQ has almost nothing to store. Just "Import from SQL". So metadata is tiny.
4.  Partitions + Refresh Logs - Large models keep partition info and last few refresh logs in storage.
5. Other objects - Images, themes, report pages embedded in the model if published as .pbix

 

# Why Model A is ~1.7GB and Model B is ~3.6GB
This is actually reversed from what I'd expect, but here's why it happens:
- If Model A uses more query folding, Power BI can discard some PQ metadata after refresh and compress it better in the .abf file.
- If Model B has many imported tables from SQL but with different data types/collations, the storage engine may store extra dictionaries.
- Also check if Model B has "Store refresh history" or more partitions enabled. Each partition adds overhead.

The key point:  VertiPaq size will always be similar because data is the same. System Storage will differ based on how the model was built.

 

# How to reduce Model A's System Storage:
1. In Power Query: Right-click queries > `Properties` > Uncheck "Enable load" for staging/derived tables you don't need in model
2. `File > Options > Current File > Data Load` > Disable "Include in report refresh" for intermediate queries
3. Reduce number of applied steps. Combine steps where possible.

Yes, I and many others have seen 2x difference in System Storage with same VertiPaq size. It's almost always Power Query metadata.

 

Hope this helps!