Gary S. answered 05/26/19
Data Architect, DBA & InFoSecurity - specializing in SQL Databases
When SET XACT_ABORT is ON, if a Transact-SQL statement raises a run-time error, the entire transaction is terminated and rolled back.
When SET XACT_ABORT is OFF, in some cases only the Transact-SQL statement that raised the error is rolled back and the transaction continues processing. Depending upon the severity of the error, the entire transaction may be rolled back even when SET XACT_ABORT is OFF. OFF is the default setting.
SET XACT_ABORT ON
instructs SQL Server to rollback the entire transaction and abort the batch when a run-time error occurs. It covers you in cases like a command timeout occurring on the client application rather than within SQL Server itself (which isn't covered by the default XACT_ABORT OFF
setting.)
Since a query timeout will leave the transaction open, SET XACT_ABORT ON
is recommended in all stored procedures with explicit transactions (unless you have a specific reason to do otherwise) as the consequences of an application performing work on a connection with an open transaction are disastrous.