Is SQL Server Slowing Down? Recent Windows Updates May Be to Blame

Is your SQL Server instance getting slower day by day after recent Windows updates were installed? It may not be a coincidence. Microsoft has just confirmed a bug that can leave linked server connections open, to the point of degrading server performance. Here’s what you need to know.

On November 11, 2026, Microsoft added a new known issue to its Windows Server 2025 health dashboard. This issue refers to updates released starting on October 13, 2026, meaning from KB5126646 for Windows Server 2025. That also means the cumulative updates released during the November 2026 Patch Tuesday, which fixed 1,093 security vulnerabilities, are included among the affected versions.

The bug affects SQL Server linked servers. As a reminder, this feature lets you query an external database directly from a SQL Server instance. To communicate with the remote source, SQL Server relies on an OLE DB provider, the data access component that acts as the interface with the other DBMS.

Connections that pile up as queries run

According to Microsoft, once these updates are installed, the connections created by linked server queries may remain open after the queries finish. The result, as you may have guessed: over time and as new queries run, "connections to external databases can accumulate instead of closing as expected", the Redmond company explains. As a result, performance can degrade over time, and an increasing number of open connections to remote databases should raise a red flag.

Microsoft says linked server queries that use OLE DB providers, including those relying on an ODBC driver through MSDASQL (a common setup for PostgreSQL with psqlODBC), are affected. Microsoft mentions connections to Oracle and PostgreSQL among the known impacted systems, without providing an exhaustive list.

To check whether you are affected, the list of linked servers is available in SSMS, under Server Objects then Linked Servers. The query SELECT name, provider FROM sys.servers WHERE is_linked = 1 can be used to display the provider in use (OraOLEDB.Oracle, MSDASQL, etc.).

Even though I mentioned Windows Server 2025 earlier, it is far from being the only affected operating system. In fact, this issue is directly tied to the OS, and it affects Windows 10, Windows 11, and Windows Server 2012 through 2025.

What are the workarounds until the fix arrives?

Microsoft does not yet offer a permanent fix. Here are the options it has outlined:

• Close idle connections: if you can identify them, closing them manually will temporarily relieve the server. On PostgreSQL, the pg_stat_activity view can be used to spot sessions opened from the SQL Server host, and the pg_terminate_backend function can close them. On Oracle, the V$SESSION view can be used to identify them, and the ALTER SYSTEM KILL SESSION command can close them.
• Restart the SQL Server service: this temporarily restores stability, although it does not prevent the issue from returning after some uptime.
• Contact support: a mitigation is available for businesses through Microsoft Support for business.

The real fix will come in the form of an out-of-band update, to be released "in the coming days", Microsoft promises.

Have you observed this behavior on your SQL Server instances?

Florian Burnel Co-founder of IT-Connect

Systems and network engineer, co-founder of IT-Connect and Microsoft MVP "Cloud and Datacenter Management". I'd like to share my experience and discoveries through my articles. I'm a generalist with a particular interest in Microsoft solutions and scripting. Enjoy your reading.

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