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Microsoft - Microsoft SQL Server - SQL - Trace Flags

Trace flags are used to set specific server characteristics or to alter a particular behavior.

Trace flags are frequently used to diagnose performance issues or to debug stored procedures or complex computer systems, but they may also be recommended by Microsoft Support to address behavior that is negatively impacting a specific workload.
All documented trace flags and those recommended by Microsoft Support are fully supported in a production environment when used as directed.

There are three scopes at which trace flags can work:
- Query: Query trace flags are active for the context of a specific query.
- Session: Session trace flags are active for a connection and are visible only to that connection.
- Global: Global trace flags are set at the server level and are visible to every connection on the server.
Some flags can only be enabled as global, and some can be enabled at either global or session scope.

NOTE: It is advisable to carefully review any trace flags that are used.

It is recommended to test the flag in a non-production environment before deploying.