Troubleshooting Azure SQL Data Warehouse

This topic lists some of the more common troubleshooting questions we hear from our customers.


Issue Resolution
Login failed for user 'NT AUTHORITY\ANONYMOUS LOGON'. (Microsoft SQL Server, Error: 18456) This error occurs when an AAD user tries to connect to the master database, but does not have a user in master. To correct this issue either specify the SQL Data Warehouse you wish to connect to at connection time or add the user to the master database. See Security overview article for more details.
The server principal "MyUserName" is not able to access the database "master" under the current security context. Cannot open user default database. Login failed. Login failed for user 'MyUserName'. (Microsoft SQL Server, Error: 916) This error occurs when an AAD user tries to connect to the master database, but does not have a user in master. To correct this issue either specify the SQL Data Warehouse you wish to connect to at connection time or add the user to the master database. See Security overview article for more details.
CTAIP error This error can occur when a login has been created on the SQL server master database, but not in the SQL Data Warehouse database. If you encounter this error, take a look at the Security overview article. This article explains how to create create a login and user on master and then how to create a user in the SQL Data Warehouse database.
Blocked by Firewall Azure SQL databases are protected by server and database level firewalls to ensure only known IP addresses have access to a database. The firewalls are secure by default, which means that you must explicitly enable and IP address or range of addresses before you can connect. To configure your firewall for access, follow the steps in Configure server firewall access for your client IP in the Provisioning instructions.
Cannot connect with tool or driver SQL Data Warehouse recommends using SSMS, SSDT for Visual Studio, or sqlcmd to query your data. For more details on drivers and connecting to SQL Data Warehouse, see Drivers for Azure SQL Data Warehouse and Connect to Azure SQL Data Warehouse articles.


Issue Resolution
Visual Studio object explorer is missing AAD users This is a known issue. As a workaround, view the users in sys.database_principals. See Authentication to Azure SQL Data Warehouse to learn more about using Azure Active Directory with SQL Data Warehouse.
Manual scripting, using the scripting wizard, or connecting via SSMS is slow, hung, or producing errors Please make sure that users have been created in the master database. In scripting options, also make sure that the engine edition is set as “Microsoft Azure SQL Data Warehouse Edition” and engine type is “Microsoft Azure SQL Database”.


Issue Resolution
Query performance troubleshooting If you are trying to troubleshoot a particular query, start with Learning how to monitor your queries.
Poor query performance and plans often is a result of missing statistics The most common cause of poor performance is lack of statistics on your tables. See Maintaining table statistics for details on how to create statistics and why they are critical to your performance.
Low concurrency / queries queued Understanding Workload management is important in order to understand how to balance memory allocation with concurrency.
How to implement best practices The best place to start to learn ways to improve query performance is SQL Data Warehouse best practices article.
How to improve performance with scaling Sometimes the solution to improving performance is to simply add more compute power to your queries by Scaling your SQL Data Warehouse.
Poor query performance as a result of poor index quality Some times queries can slowdown because of Poor columnstore index quality. See this article for more information and how to Rebuild indexes to improve segment quality.

System management

Issue Resolution
Msg 40847: Could not perform the operation because server would exceed the allowed Database Transaction Unit quota of 45000. Either reduce the DWU of the database you are trying to create or request a quota increase.
Investigating space utilization See Table sizes to understand the space utilization of your system.
Help with managing tables See the Table overview article for help with managing your tables. This article also includes links into more detailed topics like Table data types, Distributing a table, Indexing a table, Partitioning a table, Maintaining table statistics and Temporary tables.
Transparent data encryption (TDE) progress bar is not updating in the Azure Portal You can view the state of TDE via powershell.


Issue Resolution
Load fails because of large rows Currently large row support is not available for Polybase. This means that if your table contains VARCHAR(MAX), NVARCHAR(MAX) or VARBINARY(MAX), External tables cannot be used to load your data. Loads for large rows is currently only supported through Azure Data Factory (with BCP), Azure Stream Analytics, SSIS, BCP or the .NET SQLBulkCopy class. PolyBase support for large rows will be added in a future release.
bcp load of table with MAX data type is failing There is a known issue which requires that VARCHAR(MAX), NVARCHAR(MAX) or VARBINARY(MAX) be placed at the end of the table in some scenarios. Try moving your MAX columns to the end of the table.

Differences from SQL Database

Issue Resolution
Unsupported SQL Database features See Unsupported table features.
Unsupported SQL Database data types See Unsupported data types.
DELETE and UPDATE limitations See UPDATE workarounds, DELETE workarounds and Using CTAS to work around unsupported UPDATE and DELETE syntax.
MERGE statement is not supported See MERGE workarounds.
Stored procedure limitations See Stored procedure limitations to understand some of the limitations of stored procedures.
UDFs do not support SELECT statements This is a current limitation of our UDFs. See CREATE FUNCTION for the syntax we support.

Next steps

If you are were unable to find a solution to your issue above, here are some other resources you can try.