Diagnosing Slow SQL Server Row-Level Security Predicate Functions on Windows 11 25H2

Symptoms

• SQL queries with RLS predicates experience high latency on Windows 11 25H2
• Increased CPU usage during execution of predicate functions
• Delayed response times in applications relying on SQL Server RLS
• No errors in SQL Server logs but overall query throughput reduced

Likely causes

• Windows 11 25H2 system process interference causing resource contention
• Outdated or incompatible SQL Server Native Client or ODBC drivers
• Windows Defender or third-party antivirus scanning SQL Server processes or predicate function execution
• Excessive context switching due to Windows scheduler changes in 25H2 impacting predicate function threads

What FixWin checks

• Verify Windows Update status and confirm latest cumulative updates for 25H2 are installed
• Check Windows Defender exclusions for SQL Server executables and directories
• Review SQL Server Native Client and ODBC driver versions for compatibility with Windows 11 25H2
• Inspect Windows Event Viewer Application and System logs for warnings/errors during predicate execution
• Use Windows Performance Recorder (WPR) to capture CPU and thread activity during slow predicate execution

AI diagnostic workflow

• Open Event Viewer (eventvwr.msc) and filter for SQL Server-related warnings or errors during slow query times
• Run SQL Server Profiler to trace predicate function execution and identify slow operations
• Launch Windows Performance Recorder to capture CPU scheduling and context switching data during predicate execution
• Temporarily disable Windows Defender real-time protection and test predicate function performance
• Update SQL Server Native Client and ODBC drivers to latest versions supporting Windows 11 25H2

Related Windows entities

• Windows Defender Antivirus service
  Real-time scanning can impact SQL Server predicate function execution by introducing latency or CPU overhead.
• SQL Server Native Client driver
  Outdated or incompatible drivers can degrade predicate function performance on Windows 11 25H2.
• Windows Performance Recorder (WPR) tool
  Captures detailed CPU and thread activity to diagnose performance issues affecting predicate functions.
• Event Viewer - Application and System logs log
  Logs can reveal warnings or errors related to predicate function delays or system resource contention.
• Windows Scheduler component
  Changes in thread scheduling behavior in Windows 11 25H2 may cause increased context switching affecting predicate execution.

Repair logic

Begin by ensuring Windows 11 25H2 is fully updated to address known system performance issues. Next, exclude SQL Server processes from real-time antivirus scanning to reduce CPU overhead. Verify and update SQL Server Native Client and ODBC drivers to the latest Windows 11 compatible versions. Use Windows Performance Recorder to identify CPU scheduling delays or excessive context switching during predicate function execution. Address any system-level resource contention or driver incompatibilities found. Finally, monitor Event Viewer logs to confirm resolution of performance bottlenecks impacting RLS predicates.

FAQ

Why are my SQL Server Row-Level Security predicates slow only on Windows 11 25H2?

Windows 11 25H2 introduced system scheduler changes and updated security features that can cause increased CPU context switching and resource contention, impacting predicate function execution speed.

Can antivirus software cause slow SQL Server predicate functions?

Yes, real-time scanning by Windows Defender or third-party antivirus can add CPU overhead and latency when SQL Server executes predicate functions, slowing query performance.

How can I confirm if Windows components are causing the slowdown?

Use Windows Performance Recorder to capture CPU and thread activity during predicate execution, and review Event Viewer logs for system warnings. Disabling antivirus real-time protection temporarily can also help isolate the cause.

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