When it's necessary to check ##trancount > 0 in try catch block? - sql-server

Question

Sometimes I saw the following code snippet. When is the if ##trancount > 0 necessary with begin try? Both of them? Or it's a safe way(best practice) to check it always in case it's rollback before the check?
begin tran
begin try
... just several lines of sql ...
if ##trancount > 0 commit tran
end try
begin catch
if ##trancount > 0 rollback tran
end catch

Answer 1

I can think of a few scenarios to consider when dealing with ##trancount:
The current transaction was called from another stored procedure which had
its own transaction
The current transaction was called by some .NET code with its own
transaction
The current transaction is the only transaction
I believe Remus Rusanu's Exception handling and nested transactions handles all these possibilities.

Answer 2

when u don't use ##trancount, the error message of nested transaction stored procedure does not return the exact cause of error just reurtn "The rollback transaction request has no corresponding begin transaction",otherwise it gives exact cause of error, so its easy to handle the error with proper syntax.

Answer 3

To answer the question - the time to do a ##trancount check is if the code in the middle could potentially have already performed the commit or rollback of the transaction you started. So if you are calling stored procedures for example - then perform the checks at the end.
Incidentally rather than doing an if ##trancount > 0 I would suggest it is better to check the ##trancount at the start of your block of code, and then see if the count has gone up by the end, in which case do the commit or rollback, depending on try/catch.
Particularly if you are in a trigger, because the ##trancount will always be 1 there, so just doing a ##trancount > 0 could cause an error.
But even if your code is just in a stored procedure, supposed it was called by another procedure that itself has an open transaction, if your code errors and rolls back, then the outer stored procedure will have its transaction rolled back also (see https://www.sqlskills.com/blogs/paul/a-sql-server-dba-myth-a-day-2630-nested-transactions-are-real/).
So
BEGIN TRAN
PRINT ##TRANCOUNT
BEGIN TRAN
PRINT ##TRANCOUNT
ROLLBACK TRAN
PRINT ##TRANCOUNT
Will print this output:
1
2
0
So basically - if the code in the middle is calling other procedures, you need to perform the IF ##TRANCOUNT check.

Answer 4

the reason of check is if you commit trans or rollback it when ##trancount=0 you get an exception with this error message :
The COMMIT TRANSACTION request has no corresponding BEGIN TRANSACTION.

Answer 5

PRINT ##TRANCOUNT
-- The BEGIN TRAN statement will increment the
-- transaction count by 1.
BEGIN TRAN
PRINT ##TRANCOUNT
BEGIN TRAN
PRINT ##TRANCOUNT
-- The COMMIT statement will decrement the transaction count by 1.
COMMIT
PRINT ##TRANCOUNT
COMMIT
PRINT ##TRANCOUNT
--Results
--0
--1
--2
--1
--0

Answer 6

PRINT ##TRANCOUNT
-- The BEGIN TRAN statement will increment the
-- transaction count by 1.
BEGIN TRAN
PRINT ##TRANCOUNT
BEGIN TRAN
PRINT ##TRANCOUNT
-- The ROLLBACK statement will clear the ##TRANCOUNT variable
-- to 0 because all active transactions will be rolled back.
ROLLBACK
PRINT ##TRANCOUNT
--Results
--1
--0