topic Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG in Data Engineering

Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

J-Dixon — Tue, 05 Aug 2025 14:41:06 GMT

Trying out the new Materialized Lake Views in a lakehouse on Fabric

I've created two views in two different schemas with the same name. The use case is each schema represents pre-filtered populations of records, where the attributes and structure of the table are the same

When attempting to load the lineage view of the MLVs, I get the error in the title. I assume the tool cannot handle multiple MLV with the same name despite different schema

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

J-Dixon — Tue, 05 Aug 2025 15:55:03 GMT

Update -

I changed the name of the second MLV and the same error still occurs, so this isn't due to same naming

I dropped all MLVs and started from scratch. Adding first MLV works as expected, adding the second (different name) which depends on the first, causes the error described

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

Joniswe — Tue, 05 Aug 2025 19:56:07 GMT

HI J-Dixon

I have same problem, I have not found root cause yet.

I have different names on my mlv:s but if I remove all mlv:s except the first one it works

BR Jonas

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

v-kpoloju-msft — Wed, 06 Aug 2025 07:13:54 GMT

Hi @J-Dixon,
Thank you for reaching out to the community and sharing the details of your scenario.

Based on the error "name already exists in the DAG" and your scenario, it appears that the lineage view in Microsoft Fabric currently does not support multiple Materialized Lake Views (MLVs) with the same name, even if they are in different schemas.

Recommended Action: Please try renaming one of the MLVs so that each has a unique name, even if their structure is identical. Once this is done, retry the lineage view it should load without issues. We recognize that using identical names across schemas is a valid architectural pattern, and this may be a limitation in the current DAG engine.

Kindly refer to the below mentioned links for better understanding:
Manage Fabric Materialized Lake Views Lineage - Microsoft Fabric | Microsoft Learn
Materialized lake views Spark SQL reference - Microsoft Fabric | Microsoft Learn

Hope this helps clarify things and let me know what you find after giving these steps a try happy to help you investigate this further.

Thank you for using the Microsoft Fabric Community Forum.

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

J-Dixon — Wed, 06 Aug 2025 08:33:04 GMT

Hi, as mentioned in the other comment, removing and re-creating the MLV with a different name causes the same error. I'm seeing the same behaviour as the other commenter, this error happens whenever a second MLV is created, despite different naming

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

v-kpoloju-msft — Thu, 07 Aug 2025 04:40:17 GMT

Hi @J-Dixon.,

Thanks for the update. From what you have described and the error message "name already exists in the DAG," it seems like the issue is related to lineage conflicts within the Materialized Lake View (MLV) DAG not just a duplicate view name.

This typically happens in a few scenarios: Reusing the same source table or logic across multiple MLVs. Residual metadata or lineage from a previously deleted MLV still being cached. Creating a second MLV without refreshing the DAG.

To help you troubleshoot, I would recommend checking out the following Microsoft Fabric docs for more details and best practices:

Manage Fabric Materialized Lake Views Lineage - Microsoft Fabric | Microsoft Learn
Materialized lake views Spark SQL reference - Microsoft Fabric | Microsoft Learn

Data Quality in Materialized Lake Views in a Lakehouse in Microsoft Fabric - Microsoft Fabric | Microsoft Learn

Suggested workaround: After deleting an MLV, wait a few minutes or manually refresh the DAG before creating another one. Also, try using unique names for both the MLV and any CTEs or logic behind it. If possible, test creating the view in a separate Lakehouse to help isolate the issue.

Let me know if the issue continues after trying these steps happy to help further.
Thank you for using the Microsoft Fabric Community Forum.

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

J-Dixon — Thu, 07 Aug 2025 08:16:05 GMT

Thanks for your reply. I think the feature is currently broken

I created an entirely new lakehouse and created two simple MLV, where one references the other. The MLV have different names and are in different schemas, this reproduces the same error. I am not using CTE

I'm happy to provide further information if needed, thanks

EDIT: I think the dependency between MLV is what breaks the DAG. I dropped the second MLV and created a new one directly from the base tables. The lineage view is generated without error. This seems like a pretty major bug

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

v-kpoloju-msft — Thu, 07 Aug 2025 08:44:33 GMT

Hi @J-Dixon
Thanks for confirming and sharing your detailed observations.

You are right it looks like creating dependent MLVs (one referencing another) is currently causing a DAG conflict, even across different schemas and names. Since recreating the second MLV directly from base tables works, this does point to a limitation or bug in handling MLV dependencies.

I will flag this internally for further review. Meanwhile, as a workaround, it is best to avoid chaining MLVs for now and build each one directly from base tables.

Appreciate your patience and inputs, if you have any doubts feel free to share with us.
Thank you.

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

v-kpoloju-msft — Sun, 10 Aug 2025 12:25:11 GMT

Hi @J-Dixon,

Just checking in to see if the issue has been resolved on your end. If the earlier suggestions helped, that’s great to hear! And if you’re still facing challenges, feel free to share more details happy to assist further.

Thank you.

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

J-Dixon — Mon, 11 Aug 2025 08:04:51 GMT

Hey, unfortunately this is not resolved. The only way to not get the DAG error is to create totally independant MLV that are not dependent on each other, which defeats the point of the feature. Please let me know the best way to report this issue?

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

v-kpoloju-msft — Mon, 11 Aug 2025 09:25:00 GMT

Hi @J-Dixon,

Thanks for the update. When the intended use of MLVs is to have them reference each other. Since the behaviour you are describing sounds like it may be a product issue, the best next step would be to raise it through Microsoft’s official support channels so the product team can investigate.

Please consider raising a Microsoft support ticket. You can create a Microsoft support ticket using the link below:
How to create a Fabric and Power BI Support ticket - Power BI | Microsoft Learn

When submitting, it helps to include:

A brief summary of the issue.
Steps to reproduce (including how your MLVs are set up).
Screenshots or the exact DAG error message.

This way, the engineering team will have the right context to reproduce and address the behaviour.

Thank you for using the Microsoft Community Forum.

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

v-kpoloju-msft — Thu, 14 Aug 2025 04:01:59 GMT

Thank you.

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

J-Dixon — Thu, 14 Aug 2025 08:36:31 GMT

Hey, I've raised a support ticket and been in touch with a support agent, who has collected some screenshots and browser traces and refered internally. No resolution yet but the ticket is still open. They agreed it's likely a bug with the preview feature

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

v-kpoloju-msft — Thu, 14 Aug 2025 11:18:26 GMT

Hi @J-Dixon,

Thanks for the update and for sharing the steps you have already taken. It’s good to know you have got a support ticket open and that the issue has been recognized as a possible bug with the preview feature. Since the ticket is still active and being looked into internally, the best approach right now is to wait for the support team’s follow-up.

Thank you.

Re: Materialized Lake Views - Couldn't load lineage - name already exists in the DAG

J-Dixon — Thu, 04 Sep 2025 07:52:54 GMT

After some sessions with Microsoft support, this was recognised as a bug and fed back to the product team

In the meantime, there is a workaround

In the MLV definitions, if you use only lowercase when referencing a schema, the feature will work correctly

This includes situations where the schema in the lakehouse uses capital letters. The definitions seem to be case-agnostic

In my scenario, I have schemas with capital letters. I created several MLV with interdependencies ensuring all references were in lowercase, and the output data and MLV lineage view is all correct