SQL Server Service Hangs After Patching. Is there an Oracle Linked Server on your server?

Investigating the service failure

by Nabil Mahmoud - SQL Server Team Lead @ Pro DBA

I came across an issue where the SQL Server service would not start after updates were installed. Updates were installed on several SQL servers. The updates completed successfully on all instances, but one instance’s service would not start.

The updates were rolled back and that made no difference. The instance still refused to start. This is a very uncommon issue. All security features were disabled on the server including anti-virus and windows defender etc. and that too made no difference.

Unfortunately there was no VM snapshot to revert the server to its state before patching. Other services were stopped in turn to figure out if this would help to get the service up and running and that didn’t help.

However, stopping and disabling the SQL Server Agent service allowed the SQL Server service to start. Starting the SQL Agent Service would crash SQL Server Service.

One of the SQL agent jobs was calling an Oracle linked server. The Oracle dll was old and not a supported Oracle client version. This was confirmed again by disabling the SQL agent and starting the SQL Server Service but then running a test connection on the Oracle Linked Server would crash the server again. The Oracle client 11 was uninstalled and version 19c was installed instead and that fixed the issue.

This was a significant P1 issue that was caused by a simple patching exercise. The takeaway from this was:

1. Before patching, back up the server. If it’s a VM, take a VM snapshot.
2. Before patching SQL server check if there are third-party components that are no longer supported and need to be patched/replaced with newer versions.
3. When troubleshooting a SQL Server service that fails to start, consider stopping other services on the server including the SQL agent