How to Fix "Out of Memory while Reading Tuples" Issue in Linked Servers with SQL Server

LinkedServer “Out of memory while reading tuples” issue

The problem described is a common issue that affects developers working with linked servers in SQL Server. A linked server is a remote database connection to another server, and it can be used to access data from the remote server as if it were a local database.

Understanding Linked Servers

Linked servers are created using the CREATE SERVER statement, which establishes a new connection to the remote server. The remote server is then specified in subsequent statements, such as EXECUTE AS or SELECT * FROM. When working with linked servers, it’s essential to understand how they interact with the remote server and the underlying database.

Background on OLE DB Providers

The error message “Out of memory while reading tuples” suggests that there is an issue with the OLE DB provider used by the linked server. OLE DB (Object-Linking and Embedding) providers are components that connect to databases and provide access to data.

In SQL Server 2012, the OLE DB provider used for linked servers is typically MSDASQL. This provider uses a combination of memory and disk space to store data, which can lead to performance issues if not managed properly.

The Problem with Linked Servers

The problem described arises when using linked servers to access large datasets. In this case, the dataset consists of 453K records, and the error occurs while reading these tuples.

There are several reasons why linked servers might cause memory-related issues:

Memory Leaks: As mentioned in the answer, third-party ODBC drivers and Ole DB providers can leak memory. This means that they allocate memory for the data being processed but fail to release it when no longer needed.
Insufficient Resources: Linked servers often rely on shared resources on the remote server. If these resources are not sufficient or if there is a high volume of requests, it can lead to performance issues.

Workarounds and Best Practices

While the problem described is specific to linked servers, some general workarounds and best practices can help mitigate similar issues:

Restart SQL Server: Restarting SQL Server can often resolve memory-related issues. However, this might not be a viable solution for production environments.
Use Third-Party Drivers in SSIS Packages: As the answer suggests, using third-party drivers in SSIS packages or other short-lived external programs can help avoid loading them in SQL Server’s address space.
Monitor Memory Usage: Regularly monitoring memory usage and resource allocation on the remote server can help identify potential issues before they become critical.
Optimize Linked Server Configuration: Optimizing linked server configuration, such as adjusting buffer sizes or tweaking connection settings, can also improve performance.

Solution: Periodic Restart of SQL Server

One possible solution is to periodically restart SQL Server. This approach can be effective if the issue arises due to memory leaks or insufficient resources on the remote server.

However, restarting SQL Server should only be considered a temporary workaround until the underlying issue is resolved. It’s essential to identify and address the root cause of the problem rather than relying solely on periodic reboots.

Example Use Cases

Here are some example use cases where linked servers might encounter memory-related issues:

Large-scale Data Import: When importing large datasets from external sources, linked servers can experience performance issues due to insufficient resources or memory leaks.
Real-time Reporting: Real-time reporting applications often rely on linked servers to access data from remote databases. In such cases, optimizing linked server configuration and monitoring resource allocation is crucial to ensure smooth performance.

Code Example

Here’s an example code snippet that demonstrates how to create a linked server and execute a query:

{< highlight sql >}
-- Create a linked server
CREATE SERVER RWPRODMAIN
    WITH
        AUTHENTICATION = 'SQL Server Authentication'
        IDENTITY = 'SQL Server'

-- Attach the linked server
EXEC sp_addlinkedsrvlogin '@server=RWPRODMAIN', @user='username', @password='password', @localusername=''
GO

-- Create a temporary table on the remote server
CREATE TABLE [RWPRODMAIN].[dwh001].[apps_u001].quotestpremium AS
SELECT * FROM [RWPRODMAIN].[dwh001].[apps_u001].quotespremium

Note that this example assumes a specific database schema and configuration. Always consult the relevant documentation for your specific use case.

Conclusion

The “Out of memory while reading tuples” issue is a common problem when working with linked servers in SQL Server. While it’s not possible to completely eliminate the risk of memory-related issues, understanding the underlying causes and implementing best practices can help mitigate these problems.

By restarting SQL Server periodically or using third-party drivers in short-lived external programs, developers can minimize the impact of memory leaks or insufficient resources on the remote server. Regular monitoring of resource allocation and optimizing linked server configuration are also essential to ensure smooth performance.

Last modified on 2024-12-03