AG instance not in sync

Question

AG instance not in sync

Chaitanya Kiran 841

We have 8 databases in an instance. All 8 databases are members of Availability Group. On the secondary replica, the whole instance is not synchronizing . Could you please advise how to bring the secondary instance as synchronized

Thanks,

Chaitanya

Erland Sommarskog 136.7K Reputation points MVP Volunteer Moderator

2026-07-23T12:41:21.2633333+00:00

What troubleshooting have you conducted this far? Have you checked for error messages in the SQL Server error log? The cluster logs? (Or is this a clusterless AG?). How is authentication set up for the AG? Certificates? Logins? What does SELECT at-at-version say on the two nodes?

1 answer

Your answer

Erland Sommarskog 136.7K Reputation points MVP Volunteer Moderator

2026-07-23T12:41:21.2633333+00:00

What troubleshooting have you conducted this far? Have you checked for error messages in the SQL Server error log? The cluster logs? (Or is this a clusterless AG?). How is authentication set up for the AG? Certificates? Logins? What does SELECT at-at-version say on the two nodes?

Answer 1

There are a lot of reasons this could be, but you will find the first clue in your Errorlogs. If you see disconnections regarding replicas, then you can have this happen. Check your Synchronization modes of your AG (Right Click on the Availability Group in SSMS and choose Properties and look at the Synchronization mode (Asynchronous or Synchronous).

Another way to see is to right click on the Availability Group and choose Show Dashboard and see what the warnings are by seeing the Yellow ! and clicking on the link to see why it is not in sync.

Another cause could be that something happened to the replica and it was offline or disconnected and log backups happened, so you would need to restore the logs to the secondary to catch it up to the primary.

But the Dashboard and errorlogs should be a good help to find out what the deal is.