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itsmebvk's avatar
itsmebvk
Continued Contributor
2 years ago
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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     I created a new semanti...
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  • itsmebvk's avatar
    itsmebvk
    2 years ago

    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

     

     

    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.

     

     

     

     

    Before Refresh :

     

     

    After Refresh :

     

     

     

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

     

    Thanks again for your inputs.

tackytechtom's avatar
tackytechtom
Most Valuable Professional
2 years ago

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/

itsmebvk's avatar
itsmebvk
Continued Contributor
2 years ago

 

Hi tackytechtom ,

 

Thanks for your quick reply.

 

To answer your observations. 

 

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

 

 

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

 

 

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)

 

 

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

 

 

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

 

 

 

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

 

Any other inputs ?

 

  • itsmebvk's avatar
    itsmebvk
    Continued Contributor
    2 years ago

    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

     

     

    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.

     

     

     

     

    Before Refresh :

     

     

    After Refresh :

     

     

     

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

     

    Thanks again for your inputs.