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itsmebvk
Continued Contributor
Continued Contributor

New Semantic Model Fallback Even There Is no Difference with Default Semantic Model

 

Hi Folks,

 

I got stuck with some strange fallback issue.

 

I created Lakehouse with small table with two columns (City, ID). This table have only two rows

 

itsmebvk_0-1707477967916.png

 

I created a new semantic model using SQL endpoint including table which we have in default dataset, i didn't make not even one changes at all.everything is same.

 

itsmebvk_1-1707478167832.png

 

when I create a reports using these semantic models the default semantic model is acting as DirectLake mode, where as newly created semantic model acting as Direct Query Mode. 

 

Using SQl profiler I gathered some traces. Based on traces I have observed that New Semantic model is hitting Lakehouse table as direct query. Please see the screenshot below for more information related to this issue.

 

 

 

 

New Semantic Model Traces: 

 

itsmebvk_6-1707480823968.png

 

 

 

itsmebvk_7-1707480860824.png

 

 

 

 

itsmebvk_8-1707480898633.png

 

 

 

itsmebvk_9-1707480949052.png

 

 

When I compare the datasets with ALM toolkit what I have observed is its changing dataformat and aggregation in new semantic model. Also partition names seems to be different. 

 

I tried modifying the Datatypes and Aggs, but as per my understnding  it further leads to fallback.

 

itsmebvk_0-1707481281125.png

 

 

itsmebvk_2-1707481942065.png

 

Am I really missing any important point or option? Please suggest.

 

Thank you.

 

Regards

BVK

1 ACCEPTED SOLUTION
itsmebvk
Continued Contributor
Continued Contributor

@tackytechtom 

 

Ohooo I think I found the issue 🕺🕺.

 

Looks like I missed one last suggestion by MS which might leads to Fallback if we don't follow.

 

https://learn.microsoft.com/en-us/power-bi/enterprise/directlake-overview

 

itsmebvk_1-1707566310507.png

 

When you create New Semantic Model, even though following option (highlighted) enabled on New Semantic Model still we need to refresh manually as highlighted. As soon as I have done that all queries turned into Dirctlakemode and no Fallback is happening.

 

itsmebvk_2-1707566443027.png

 

 

itsmebvk_3-1707566486973.png

 

Before Refresh :

 

itsmebvk_6-1707568097183.png

 

After Refresh :

 

itsmebvk_5-1707566780908.png

 

 

itsmebvk_4-1707566734892.png

Please correct me if I am not understanding it properly. Hope this helps someone as well. 

 

Thanks again for your inputs.

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3 REPLIES 3
tackytechtom
Super User
Super User

Hi @itsmebvk ,

 

I do not have a quick solution at hand, but I spontanteously wondered wgether you are querying a table directly or a view (views do not work with Direct Lake)? Another reason could be security (RLS or OLS) that triggers the Direct Query fallback.

 

Also there is a DMV called TMSCHEMA_DELTA_TABLE_METADATA_STORAGES that has an attribute called FallbackReason that might give you some clue on what's going on 🙂

 

Hope this helps (at least a bit) 🙂

 

/Tom
https://www.tackytech.blog/
https://www.instagram.com/tackytechtom/



Did I answer your question➡️ Please, mark my post as a solution ✔️

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#proudtobeasuperuser 

 

Hi @tackytechtom ,

 

Thanks for your quick reply.

 

To answer your observations. 

 

1) I am not using views, I am using table

 

itsmebvk_0-1707534547440.png

 

2) I didn't apply security or RLS/OLS either in Lakhouse or Semantic Modle layer.

 

itsmebvk_1-1707534608832.png

 

3) I have already tried DMV you have suggested but its not showing details of object which is leading to fallback however its just showing 4 as fallback reasons for new semantic model.

 

select * from $SYSTEM.TMSCHEMA_DELTA_TABLE_METADATA_STORAGES

 

Default Semantic Model (Showing 0 Fallback reasons)

 

itsmebvk_0-1707517049110.png

 

New Semantic Model (Showing 4 Fallback reasons) but no additional details available 

 

itsmebvk_2-1707534975490.png

 

May be I am wrong, I am assuming its highlighting following four difference which happened automatically.

 

 

itsmebvk_3-1707535258257.png

 

As far as I know I strictly followed MS suggestions to avoid any fallback but still its turning into Directquery.  😞 😞 . 

 

Any other inputs ?

 

itsmebvk
Continued Contributor
Continued Contributor

@tackytechtom 

 

Ohooo I think I found the issue 🕺🕺.

 

Looks like I missed one last suggestion by MS which might leads to Fallback if we don't follow.

 

https://learn.microsoft.com/en-us/power-bi/enterprise/directlake-overview

 

itsmebvk_1-1707566310507.png

 

When you create New Semantic Model, even though following option (highlighted) enabled on New Semantic Model still we need to refresh manually as highlighted. As soon as I have done that all queries turned into Dirctlakemode and no Fallback is happening.

 

itsmebvk_2-1707566443027.png

 

 

itsmebvk_3-1707566486973.png

 

Before Refresh :

 

itsmebvk_6-1707568097183.png

 

After Refresh :

 

itsmebvk_5-1707566780908.png

 

 

itsmebvk_4-1707566734892.png

Please correct me if I am not understanding it properly. Hope this helps someone as well. 

 

Thanks again for your inputs.

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