How to fix following Error: Query failed because of connection issues to control container or control container failure.

Hi Harinath Reddy A,

Thanks for sharing the details — this is helpful.

Since your query is working fine in PySpark but failing from the SQL endpoint, this usually means the issue is not with the data itself, but with how the serverless SQL pool is trying to access your ADLS Gen2 storage.

The error you’re seeing:

“Query failed because of connection issues to control container or control container failure”
is commonly related to storage access, networking, or sometimes a temporary backend issue.

**
**What I’d suggest checking
1. Storage permissions
First, please make sure the SQL endpoint has proper access to your storage account:

• If you’re using Managed Identity → it should have at least Storage Blob Data Reader role
• If you’re using SAS or credentials → double-check that they are still valid and not expired

As a quick test, you can try querying the file directly using OPENROWSET. This helps confirm whether the SQL endpoint can actually reach the storage.
2. Storage networking settings
If your storage account has firewall rules or private endpoints enabled:

• Make sure “Allow Azure services” is enabled, or
• Verify that Synapse is correctly configured with Managed VNet / private endpoint access

3. External table / file path check
Since your tables are built on CSV files:

• Confirm the files are still present in the same location
• Ensure the path hasn’t changed
• Check if there were any recent changes to file format or schema

Since the query works in PySpark, the data and storage are healthy. The issue is isolated to the serverless SQL pool’s access path (permissions, networking, or transient service condition). Following the above steps should help resolve the problem.
Microsoft Documentation

• https://learn.microsoft.com/azure/synapse-analytics/sql/resources-self-help-sql-on-demand#query-failures
• https://learn.microsoft.com/azure/synapse-analytics/sql/develop-storage-files-overview
• https://learn.microsoft.com/azure/storage/common/storage-network-security

Hope this helps. If you have any follow-up questions, please let me know. I would be happy to help.

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The error indicates an internal issue in the serverless SQL pool control plane (control container) rather than a problem with the CSV files or Spark itself. Because the same query works via Spark but fails only in serverless SQL (SSMS / Synapse SQL on-demand), the problem is specific to the serverless SQL pool execution.

For this class of internal control-container/topology issues, the documented guidance is:

1. Retry the query after some time, in case it is a transient internal failure.
2. If the error persists, file a support ticket with Azure Support and include:
   • The exact error text.
   • The workspace name and region.
   • The database and query text (or a minimized repro).
   • The approximate time and correlation IDs (if available from the error details).
   • Any unusual workload conditions (for example, sudden spike in concurrent queries, large wildcard queries, or recent changes to data layout).

This allows the Azure Synapse team to investigate the control-container failure or topology change on the service side. There is no client-side configuration change documented that resolves this specific control-container error.

References:

• Troubleshoot serverless SQL pool in Azure Synapse Analytics