Cross-Database Queries

Applies to: SQL Server

Starting with SQL Server 2014 (12.x), memory-optimized tables do not support cross-database transactions. You cannot access another database from the same transaction or the same query that also accesses a memory-optimized table. You cannot easily copy data from a table in one database, to a memory-optimized table in another database.

Table variables are not transactional. Therefore, memory-optimized table variables can be used in cross-database queries, and can thus facilitate moving data from one database into memory-optimized tables in another. You can use two transactions. In the first transaction, insert the data from the remote table into the variable. In the second transaction, insert the data into the local memory-optimized table from the variable. For more information on memory-optimized table variables, see Faster temp table and table variable by using memory optimization.

Example

This example illustrates a method to transfer data from one database into a memory-optimized table in a different database.

1. Create Test Objects. Execute the following Transact-SQL in SQL Server Management Studio.

   
   USE master;
   GO
   
   SET NOCOUNT ON;
   
   -- Create simple database
   CREATE DATABASE SourceDatabase;
   ALTER DATABASE SourceDatabase SET RECOVERY SIMPLE;
   GO
   
   -- Create a table and insert a few records
   USE SourceDatabase;
   
   CREATE TABLE SourceDatabase.[dbo].[SourceTable] (
   	[ID] [int] PRIMARY KEY CLUSTERED,
   	[FirstName] nvarchar(8)
   	);
   
   INSERT [SourceDatabase].[dbo].[SourceTable]
   VALUES (1, N'Bob'),
   	(2, N'Susan');
   GO
   
   -- Create a database with a MEMORY_OPTIMIZED_DATA filegroup
   
   CREATE DATABASE DestinationDatabase
    ON  PRIMARY 
   ( NAME = N'DestinationDatabase_Data', FILENAME = N'D:\DATA\DestinationDatabase_Data.mdf',	SIZE = 8MB), 
    FILEGROUP [DestinationDatabase_mod] CONTAINS MEMORY_OPTIMIZED_DATA  DEFAULT
   ( NAME = N'DestinationDatabase_mod', FILENAME = N'D:\DATA\DestinationDatabase_mod', MAXSIZE = UNLIMITED)
    LOG ON 
   ( NAME = N'DestinationDatabase_Log', FILENAME = N'D:\LOG\DestinationDatabase_Log.ldf', SIZE = 8MB);
   
   ALTER DATABASE DestinationDatabase SET RECOVERY SIMPLE;
   GO
   
   USE DestinationDatabase;
   GO
   
   -- Create a memory-optimized table
   CREATE TABLE [dbo].[DestTable_InMem] (
   	[ID] [int] PRIMARY KEY NONCLUSTERED,
   	[FirstName] nvarchar(8)
   	)
   WITH ( MEMORY_OPTIMIZED = ON, DURABILITY = SCHEMA_AND_DATA );
   GO
   

2. Attempt cross-database query. Execute the following Transact-SQL in SQL Server Management Studio.

   INSERT [DestinationDatabase].[dbo].[DestTable_InMem]
   SELECT * FROM [SourceDatabase].[dbo].[SourceTable]
   

   You should receive the following error message:

   Msg 41317, Level 16, State 5
   A user transaction that accesses memory optimized tables or natively compiled modules cannot access more than one user database or databases model and msdb, and it cannot write to master.

3. Create a memory-optimized table type. Execute the following Transact-SQL in SQL Server Management Studio.

   USE DestinationDatabase;
   GO
   
   CREATE TYPE [dbo].[MemoryType]  
       AS TABLE  
       (  
   	[ID] [int] PRIMARY KEY NONCLUSTERED,
   	[FirstName] nvarchar(8)
       )  
       WITH  
           (MEMORY_OPTIMIZED = ON);  
   GO
   

4. Re-attempt the cross-database query. This time the source data will first be transferred to a memory-optimized table variable. Then the data from the tale variable will be transferred to the memory-optimized table.

   -- Declare table variable utilizing the newly created type - MemoryType
   DECLARE @InMem dbo.MemoryType;
   
   -- Populate table variable
   INSERT @InMem SELECT * FROM SourceDatabase.[dbo].[SourceTable];
   
   -- Populate the destination memory-optimized table
   INSERT [DestinationDatabase].[dbo].[DestTable_InMem] SELECT * FROM @InMem;
   GO 
   

See Also

Migrating to In-Memory OLTP