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Introduction to Stretch Databases – Part Three

Continuing with my earlier posts on Stretch Databases – Part1, Part2, I will discuss some key aspects to keep in mind when we stretch a database.

Note- SQL Server 2016 is still in preview and some of this information can change in the future.

Insert, Update and Delete

As I had mentioned in my earlier posts, once the records have been moved to the remote Azure Databases, it cannot be Deleted/Updated from the local server. All updates/deletes would need to be run on the Remote Server explicitly. The following error would be returned if an attempt is made to update/insert the record, which is already on the remote server.

Update and delete of rows eligible for migration in table ‘Test_RemoteArchive’ is not allowed because of the use of REMOTE_DATA_ARCHIVE.
Msg 3609, Level 16, State 1, Line 3
The transaction ended in the trigger. The batch has been aborted.

New data which is inserted into the table, get inserted to the local table first and then get archived to the remote server at a later point in time.

Select Operations

As previously mentioned, Select operations executes the query on both the local and remote server and then concatenates the data before sending to the client. A typical query plan for queries on a Stretched tabled would look something like.

If SQL Server is not able to connect to the remote linked server (either because of network related issues or because of authentication issues) the following error would be returned.

OLE DB provider “SQLNCLI11” for linked server “ServerName” returned message “Login timeout expired”.
OLE DB provider “SQLNCLI11” for linked server “ServerName” returned message “A network-related or instance-specific error has occurred while establishing a connection to SQL Server. Server is not found or not accessible. Check if instance name is correct and if SQL Server is configured to allow remote connections. For more information see SQL Server Books Online.”.

Msg 53, Level 16, State 1, Line 3
Named Pipes Provider: Could not open a connection to SQL Server [53].

This error would also be logged in the SQL Error Log. If the connection to the Remote Server gets terminated in the middle of query execution, you would get the following error..

OLE DB provider “SQLNCLI11” for linked server “ServerName” returned message “Communication link failure”.
Msg 10054, Level 16, State 1, Line 3
TCP Provider: An existing connection was forcibly closed by the remote host.

Backup and Restore

Databases enabled for stretch can be backed up or restored just the ordinary databases. The only difference being that immediately after restore you wont be able to query the remote table data. In order to query the remote data, we first have to reconnect the database to the remote database. This can be done using the stored procedure sys.sp_reauthorize_remote_data_archive.

Exec sp_reauthorize_remote_data_archive N’sql_azure_sysadmin_username’ , N’password’
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