Relationship between Transactions in Nested Stored Procedures? - sql-server

Question

I put transactions in all my "set" procedures. No problems. Everything works.
In this case, I need one set procedure, to call another, thankfully, only once, or that would potentially complicate things further.
So the happy bath would be.
I'm in ProcA and start a transaction.
It calls ProcB and it starts a transaction.
ProcB is successful and commits.
ProcA is successful and commits.
However, what happens if ProcB fails, rollsback, and rethrows the error. It should cause ProcA to rollback as well correct?
What if ProcB succeeds, commits, then ProcA subsequently fails, and rollsback...will what happened in ProcB be rolled back? or is it commited?
I need these two to work together, either both succeed, or fail and both be rolled back. What's the best way to ensure this happens?
I'm working with Microsoft SQL Server 2008 R2 (SP1)
Note: If ProcB requires a transaction because it can be called without ProcA wrapping it. And technically, ProcA won't always call ProcB (depends on input).

Answer 1

Here's a simple demo to show what happens with nested transations:
CREATE TABLE TranTest (Field1 INTEGER)
BEGIN TRANSACTION
SELECT ##TRANCOUNT -- 1 open transaction
INSERT TranTest VALUES (1)
BEGIN TRANSACTION
SELECT ##TRANCOUNT -- 2 open transactions
INSERT TranTest VALUES (2)
ROLLBACK TRANSACTION -- this rolls back ALL transaction
SELECT ##TRANCOUNT -- 0 open transactions (you may have expected 1?)
SELECT * FROM TranTest -- No rows
Instead f the ROLLBACK above, if you did a COMMIT TRANSACTION, this actual does nothing other then decrement ##TRANCOUNT. So you then would need to to either COMMIT the outer transaction (which would COMMIT both rows to the table), or do a ROLLBACK which would result in no rows being committed to the table.
Here's the MSDN ref on nested transactions: http://msdn.microsoft.com/en-us/library/ms189336.aspx

Answer 2

Just use XACT_ABORT ON, and you are all set. Run the following script and see for yourself:
CREATE DATABASE ak_test;
GO
USE ak_test;
GO
CREATE TABLE dbo.a(i INT CONSTRAINT a_CannotInsertNegative CHECK(i>=0));
GO
CREATE TABLE dbo.b(i INT CONSTRAINT b_CannotInsertNegative CHECK(i>=0));
GO
CREATE PROCEDURE dbo.innerProc #i INT
AS
SET XACT_ABORT ON ;
BEGIN TRAN
INSERT b(i)VALUES(#i);
COMMIT;
GO
CREATE PROCEDURE dbo.outerProc #i1 INT, #i2 INT, #i3 INT
AS
SET XACT_ABORT ON ;
BEGIN TRAN
INSERT a(i)VALUES(#i1);
EXEC innerProc #i=#i2;
INSERT a(i)VALUES(#i3);
COMMIT;
GO
-- succeeds
EXEC dbo.outerProc 1, 2, 3;
SELECT * FROM dbo.a;
SELECT * FROM dbo.b;
GO
-- inner proc fails
EXEC dbo.outerProc 2, -3, 4;
GO
SELECT * FROM dbo.a;
SELECT * FROM dbo.b;
GO
-- second insert in outer proc fails
EXEC dbo.outerProc 3, 4, -5;
GO
SELECT * FROM dbo.a;
SELECT * FROM dbo.b;

Answer 3

I'm paranoid about transactions (there was this transaction left open on Production once that no one noticed for half an hour...) so I'd warp the potentially inner transaction like so:
CREATE PROCEDURE etcetc
...
DECLARE #IsTransaction bit = 0
IF ##trancount > 0
BEGIN
BEGIN TRANSACTION
SET #IsTransaction = 1
END
...
IF #IsTransaction = 1
BEGIN
COMMIT
-- or ROLLBACk, as necessary
END
All transaction processing (and handling of errors that occur within the transaction) must then be dealt with at whatever level launched the transaction.
(And did anyone else notice how BOL doesn't actually say what happens when you issue a ROLLBACK to a named transaction that isn't the outermost transaction? They do spell out every other permutation...)