Erin Stellato walks us through a troubleshooting guide when users complain about poorly-performing queries:
This is tale of troubleshooting…
When you unexpectedly or intermittently encounter a change in query performance, it can be extremely frustrating and troublesome for a DBA or developer. If you’re not using Query Store, a third-party application, or your own method to capture query data, then you probably don’t have information about what query performance looked like when things were good…you just know how it’s running now. I was working with a customer of Tim’s last week that had been chasing this exact problem for, in their words, years. They had recently upgraded to SQL Server 2016, and the problem was still occurring.
Strangely, “blame the network” didn’t appear in Erin’s post, so I don’t know if it’s comprehensive.