Dataflow generation2 was working yesterday but not today

[Dragon496]

Hello

We are currently evaluating options for moving our data from on premise to fabric.

The first thing I have to try is extract data using a dataflow. So yesterday I placed a spreadsheet, with multiple worksheets in the files area of my Lakehouse. Created a generation2 dataflow and loaded in and transformed about four of the worksheets. I also had an additional append query that combined the data.

Everything was working perfectly! But if I try and modify my dataflow today, I receive the following error:-

Microsoft SQL: A connection was successfully established with the server, but then an error occurred during the pre-login handshake. (provider: TCP Provider, error: 0 - The semaphore timeout period has expired.)

I cannot explain the following:-

Select one of the queries, which is not working, copy the M code from the advanced editor, create a new dataflow, add a blank query, paste in the M code and it works.

Any thoughts?

Thanks

[Dragon496]

Hello

Thanks for the responses. The dataflow in question is fairly straightforward-it is just retrieving data from an Excel spreadsheet, stored in a lake house. It's simply retrieves details from multiple worksheets and then uses an append query to merge them together (I think I have only used five worksheets and one append query to combine 2 of them).

I am just about to check whether either of my dataflows are still working this morning. If not I will raise a ticket.

Thanks

[v-zhouwen-msft]

Hi all,thanks for the quick reply, I'll add more.

Hi @Dragon496 ,

If you have a Pro license you can open a Pro ticket at

Power Platform admin center

Best Regards

[rohit1991]

The error you're encountering, "The semaphore timeout period has expired," typically points to a network-related issue or a temporary connectivity problem with the backend services. Here are some potential causes and troubleshooting steps:

---

1. Temporary Network Issues

• Explanation: A network glitch or timeout between your environment and the data source server could cause this issue.
• Solution: Retry after some time, ensuring there are no ongoing network disruptions.

---

2. Resource Constraints

• Explanation: If the resource usage in your environment (e.g., Lakehouse or the dataflow service) is high, this could lead to timeouts.
• Solution: Check system resource usage or try reducing query complexity.

---

3. Dataflow Configuration

• Explanation: Modifications to the dataflow might have introduced complexity or an invalid configuration.
• Solution:
  • Validate each query individually in the dataflow to identify where the failure occurs.
  • Use a simpler transformation and gradually add complexity.

---

4. Backend Service Issue

• Explanation: The Fabric backend services might be experiencing temporary issues.
• Solution:
  • Check the Microsoft Fabric Status page for any service-related issues.
  • Restart your Lakehouse and dataflow operations after verifying the service is operational.

---

5. Reauthentication

• Explanation: Sometimes, authentication tokens expire or face handshake issues.
• Solution: Reauthenticate your connection to the Lakehouse and ensure the credentials are valid.

---

6. Debugging Steps

Since copying and pasting the M code into a new dataflow works, this indicates:

• The issue might be with the existing dataflow metadata or configuration.
• Try exporting the existing dataflow, recreating it from scratch, and re-importing the M code for all queries.

[SaiTejaTalasila]

Hi @Dragon496 ,

Are you using fabric trail capacity?.

If no, you can open a ticket with Microsoft support incase if you want to get more details.

Thanks,

Sai Teja