Certain errors cannot rollback a transaction. That’s why XACT_ABORT ON should be included in the code to prevent unhandled scenarios erroring out without rolling back the transaction and leaving an open transaction. In the example below, in the first scenario – you can see the session 1 query errored out leaving an open transaction and it blocks session 2 query( under read committed isolation). In the second scenario with XACT_ABORT ON, it will rollback the transaction.
--Set up Test Table
Create Table Test(id int,Name varchar(20))
--Scenario 1 with XACT_ABORT OFF
--Session 1
Begin
Set XACT_ABORT OFF
Begin Try
Begin Tran
Insert into test values(1,'test')
Select * from Idonotexist
If (@@ERROR=0)
Commit
End Try
Begin Catch
If (@@TranCount>0)
Rollback
End Catch
End
--Session 2
select * from test
--Scenario 2 with XACT_ABORT ON
--Session 1
Begin
Set XACT_ABORT ON
Begin Try
Begin Tran
Insert into test values(1,'test')
Select * from Idonotexist
If (@@ERROR=0)
Commit
End Try
Begin Catch
If (@@TranCount>0)
Rollback
End Catch
End
--Session 2
select * from test
--Clean Up
Drop Table Test
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