How to fix Error 3645 on Windows Server 2025 / Windows 11

by

Troubleshooting Guide: SQL Server Error 3645 — “Batch Connectivity Statistics: Packets Read Time”

Why This Error Happens

Error 3645 typically surfaces when SQL Server’s diagnostic telemetry layer logs network latency statistics that exceed expected thresholds, often triggered by TCP/IP stack misconfiguration or NIC driver inefficiencies on the host machine. This is frequently compounded by outdated network drivers on Windows Server 2025/Windows 11 that fail to properly negotiate TCP offload settings with SQL Server 2025’s updated connectivity stack. In some cases, this is a benign informational message that becomes an error due to restrictive extended events session configurations capturing it as a critical trace event.

Step-by-Step Resolution Guide

Step 1: Verify Network Adapter Configuration and Drivers

  • Open Device Manager and locate your active network adapter under “Network Adapters.”
  • Right-click and select “Update Driver” — ensure you’re on the latest WHQL-certified driver for Windows Server 2025.
  • Disable TCP Chimney Offload if enabled, by running the following in an elevated PowerShell/Command Prompt:
  netsh int tcp set global chimney=disabled
  • Restart the network adapter or reboot the server to apply changes.

Step 2: Review and Adjust SQL Server Extended Events Session

  • Open SQL Server Management Studio (SSMS) and connect to the instance reporting the error.
  • Navigate to Management > Extended Events > Sessions.
  • Locate the session capturing batch_connectivity_statistics or similar network telemetry events.
  • Right-click the session, select Properties, and either disable the specific event or increase the latency threshold filter (e.g., set packets_read_time > 500ms instead of default values) to reduce noise-level logging.

Step 3: Check SQL Server Network Configuration (TCP/IP Settings)

  • Open SQL Server Configuration Manager.
  • Navigate to SQL Server Network Configuration > Protocols for [Your Instance Name].
  • Ensure TCP/IP is enabled and that the Keep Alive value under IP Addresses tab is set appropriately (default is 30000 ms; consider increasing to 60000 ms on high-latency networks).
  • Restart the SQL Server service via services.msc or by running:
  net stop MSSQLSERVER && net start MSSQLSERVER

Step 4: Apply Latest SQL Server 2025 Cumulative Update

  • Check your current build version by running:
  SELECT @@VERSION;
  • Download and install the latest Cumulative Update (CU) from the Microsoft Update Catalog if your build is not current.
  • Reboot the server post-installation to ensure all binaries are properly replaced.

Alternative or Verification Steps

  • After applying the fixes, run a connectivity stress test using sqlcmd -S servername -Q "SELECT 1" in a loop and monitor the SQL Error Log (C:\Program Files\Microsoft SQL Server\MSSQL16.MSSQLSERVER\MSSQL\Log\ERRORLOG) to confirm Error 3645 no longer appears.
  • If the error persists, consider isolating the issue by testing connectivity over a different network path (e.g., switching from a virtual NIC to a physical NIC) to rule out hypervisor-level packet inspection delays.