SQL Server: Unexpected CPU Spike on Primary Replica — Troubleshooting Assistance Needed

Question

SQL Server: Unexpected CPU Spike on Primary Replica — Troubleshooting Assistance Needed

Prakash Nandwana 0

Problem description

I am experiencing an issue with my SQL Server virtual machine where the primary replica of an Always On availability group in the UK South region is experiencing unexpected CPU utilization spikes up to 100%. This occurs under a workload that runs at approximately 30% CPU on the secondary replica. The spike was first observed on September 3, 2026, at 16:00 UTC, detected via external monitoring tools. The issue is not currently active, and no error codes have been generated. I am seeking assistance to diagnose and resolve the root cause of these CPU spikes.

Environment

A Windows Server–based virtual machine running SQL Server in the UK South region, deployed in an availability zone, configured as part of an Always On availability group with at least one primary and one secondary replica. Azure VM agent and platform metrics are enabled.

What I've already tried

I have reviewed monitoring data confirming that the sqlservr process reached 100% CPU on the primary replica while the secondary remained near 30% under the same workload. I declined to collect additional diagnostics when prompted. An initial support engineer attempted to retrieve platform data but reported 'No data found.' Automated diagnostics flagged high-CPU instances over the past 24 hours, with average max CPU above 85% in ten-minute windows and peak 30-minute average CPU about 99.8%. I have also reviewed platform diagnostic insights regarding VM resizing constraints and performed basic troubleshooting steps such as monitoring VM-level metrics and reviewing configuration settings.

Current status

I am seeking guidance from an engineer to diagnose the cause of the CPU spikes on the primary replica and to identify potential solutions or configuration adjustments to prevent recurrence. I am prepared to provide additional diagnostic data, including SQL Server audit logs, Extended Events traces, process information during the incident, and performance metrics as needed.

Himaja Y 285 Reputation points Microsoft External Staff Moderator

2026-09-05T12:46:02.9933333+00:00

Hi @Prakash Nandwana ,

Thank you for contacting Microsoft Support.

We are actively investigating the issue reported in your support request. We will provide you with an update as soon as we have more information.

Thank you for your patience and understanding.
Erland Sommarskog 137.1K Reputation points MVP Volunteer Moderator

2026-09-05T20:56:33.4433333+00:00

Do you have Query Store enabled on the instance? Query Store would be the place to collect data of which queries that were running at the time. If you do not have Query Store or any other monitoring enabled, it is not likely that you will be able to conclude what caused the spikes.

There is nothing that says that 100% CPU on the primary would be reflected on the secondary. Typically a primary and a secondary have different workloads.

What does "SELECT @@version" report?

Your answer

Himaja Y 285 Reputation points Microsoft External Staff Moderator

2026-09-05T12:46:02.9933333+00:00

Hi @Prakash Nandwana ,

Thank you for contacting Microsoft Support.

We are actively investigating the issue reported in your support request. We will provide you with an update as soon as we have more information.

Thank you for your patience and understanding.
Erland Sommarskog 137.1K Reputation points MVP Volunteer Moderator

2026-09-05T20:56:33.4433333+00:00

Do you have Query Store enabled on the instance? Query Store would be the place to collect data of which queries that were running at the time. If you do not have Query Store or any other monitoring enabled, it is not likely that you will be able to conclude what caused the spikes.

There is nothing that says that 100% CPU on the primary would be reflected on the secondary. Typically a primary and a secondary have different workloads.

What does "SELECT @@version" report?