Facing "Failed to detect schema" error in Synapse Analytics when ingesting a valid CSV from Data Lake. All configurations seem correct.

Question

I am attempting to fetch and ingest a CSV file from Azure Data Lake into Azure Synapse Analytics. However, I'm consistently encountering an error that states "Failed to detect schema. Please review and update the file format settings to allow file schema detection."

Key Details:

CSV File Validity: I have verified the CSV file by downloading and reviewing it. It is formatted correctly, has appropriate delimiters, and the header row seems to be in order.

Storage Access: The CSV is stored in Azure Data Lake Storage. I have ensured that public network access is enabled from all networks. When trying to fetch more details regarding the error, it also stated, "We failed to open the storage path." However, given the access settings and other configurations, this shouldn't be an issue.

1. Configuration in Synapse Studio: I have also ensured that while setting up the data flow in Synapse Studio, the file format for the lake database was set to CSV.

Despite the correct configurations and file format, the schema detection process fails, preventing further data operations.

I am seeking assistance to understand and resolve the root cause of this issue. Any insights, troubleshooting steps, or configurations that I might have overlooked would be greatly appreciated.

Answer 1

Hi @Taro Casalino

Based on my understanding of the error message you provided, it appears that the issue may be related to schema detection.
Before we proceed, could you please clarify whether you are attempting to use the copy activity to load data from a CSV into Synapse, writing a notebook, or creating an external table on top of an ADLS file?
To address this issue, we can proceed with the following steps:

1. Check if the CSV file has any data type mismatches in the columns. Synapse Analytics might not be able to detect the schema if the data types in the columns do not match the expected data types. Ensure that the data types in the columns match the expected data types.
2. Check if the CSV file has any special characters or encoding that might be causing issues with schema detection. If the file has any special characters remove them and try ingesting the file again. You can also try changing the encoding of the file to UTF-8, which is the recommended encoding for CSV files in Synapse Analytics.
3. Check if there are any issues with the Azure Data Lake Storage account. Ensure that the storage account is accessible and that the correct permissions are set for the account. You can also try creating a new storage account and ingesting the file into the new account to see if the issue persists.
4. Check if there are any issues with the Synapse Analytics workspace. Ensure that the workspace is accessible and that the correct permissions are set for the workspace. You can also try creating a new workspace and ingesting the file into the new workspace to see if the issue persists.
5. If the issue persists, you can try ingesting the CSV file using other methods, such as using Azure Data Factory or Azure Databricks. These services provide additional options for configuring schema detection and data ingestion.                                          

Here are some relevant documentation links that can help you with the above steps:

• Supported file formats and compression codecs in Synapse Analytics
• Define schema for a data flow in Synapse Studio
• Ingest data from Azure Data Lake Storage Gen1 using Azure Data Factory

 I hope this information is useful! Feel free to ask if you have any more questions.
Hope this helps. Do let us know if you any further queries.

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