SqlBulkCopy throws InvalidOperationException when using Azure SQL with managed identity on .NET 8

[priyankatiwari08]

Describe the bug

When performing a SqlBulkCopy operation against Azure SQL Database using Azure AD managed identity authentication (via ActiveDirectoryManagedIdentity), the operation throws an InvalidOperationException with message "Internal connection fatal error" after copying approximately 50,000 rows.

This was working correctly in SqlClient 5.1.6. After upgrading to 5.2.1, the bulk copy operation fails intermittently.

To Reproduce

using var connection = new SqlConnection(
    "Server=myserver.database.windows.net;Database=mydb;Authentication=ActiveDirectoryManagedIdentity;");
await connection.OpenAsync();

using var bulkCopy = new SqlBulkCopy(connection)
{
    DestinationTableName = "dbo.LargeTable",
    BatchSize = 10000,
    BulkCopyTimeout = 600
};

// dataReader has ~100K rows
await bulkCopy.WriteToServerAsync(dataReader);
// Throws after ~50K rows: System.InvalidOperationException: Internal connection fatal error

Expected behavior

SqlBulkCopy.WriteToServerAsync should complete successfully for all 100K rows, as it did with SqlClient 5.1.6.

Actual behavior

Throws System.InvalidOperationException: Internal connection fatal error after ~50,000 rows are copied.

Further technical details

• Microsoft.Data.SqlClient version: 5.2.1
• .NET target framework: .NET 8.0
• SQL Server version: Azure SQL Database (latest)
• Operating system: Ubuntu 22.04 (Azure App Service Linux)

Stack trace

System.InvalidOperationException: Internal connection fatal error
   at Microsoft.Data.SqlClient.TdsParser.TryRun(...)
   at Microsoft.Data.SqlClient.SqlBulkCopy.WriteToServerInternalAsync(...)
   at Microsoft.Data.SqlClient.SqlBulkCopy.WriteToServerAsync(DbDataReader reader)

[github-actions]

🔍 Triage Summary

Check	Result
Issue type	Bug
Environment	All required environment details provided for investigation
Area	Area\Sql Bulk Copy
Duplicates	None found
Regression	Likely regression from v5.1.6 → v5.2.1

Analysis

This issue reports that SqlBulkCopy.WriteToServerAsync throws System.InvalidOperationException: Internal connection fatal error after approximately 50,000 rows when connecting to Azure SQL Database using ActiveDirectoryManagedIdentity authentication on .NET 8 / Ubuntu 22.04. The stack trace points directly into TdsParser.TryRun via SqlBulkCopy.WriteToServerInternalAsync, suggesting the TDS connection is being fatally terminated mid-operation during a large async bulk copy. Since this regressed between 5.1.6 and 5.2.1, changes in the bulk copy async execution path, the managed identity token refresh logic, or TDS connection state management introduced between those versions are prime suspects. Severity: P1 — confirmed regression affecting production bulk data workloads on Azure SQL with managed identity.

Next Steps

• Assign this issue to the Copilot coding agent to investigate the regression between v5.1.6 and v5.2.1.
• Investigation should focus on:
  1. Changes to SqlBulkCopy.WriteToServerInternalAsync and SqlBulkCopy.cs between 5.1.6 and 5.2.1 — look for changes in connection state handling or batch commit logic.
  2. Token renewal/refresh during long-running bulk copy operations with ActiveDirectoryManagedIdentity — the failure at ~50K rows (midpoint of 100K) could indicate a token expiry or retry path that corrupts connection state.
  3. TDS connection state transitions in TdsParser.TryRun during large bulk copy batches — check for any new error handling or cancellation paths that could trigger a fatal error.
  4. Any changes to how async bulk copy handles managed SNI (since this runs on Linux/Managed SNI path).

Note: This triage summary is auto-generated by an AI agent. The analysis and suggestions above have not been verified by a human maintainer. Please treat as preliminary guidance only.

Generated by SqlClient Issue Auto-Triage for issue #30 · ● 581.6K · ◷