asked on Deadlock simulation example...
Following an example from a book displayed on the image, I am executing code a and b given below starting at steps:
1a, 1b, 2a, 2c, 3a, 3c, etc.
Question: Why am I not coming across <blocked> at step 6b? Please see the image for 6b.
![TranBlocked]()
Cose a:
Code b:
1a, 1b, 2a, 2c, 3a, 3c, etc.
Question: Why am I not coming across <blocked> at step 6b? Please see the image for 6b.
Cose a:
--1a
use TSQL2012;
begin tran
select '--1a: ' + cast(@@TRANCOUNT as varchar(10)), @@TRANCOUNT
--2a
update hr.Employees
set phone= N'10004'
where empid= 1
select '--2a: ' + cast(@@TRANCOUNT as varchar(10)), @@TRANCOUNT
--3a
--(excute next in b)
--4a
update Production.Suppliers
set fax= N'555-1212'
where supplierid= 1
select '--4a: ' + cast(@@TRANCOUNT as varchar(10)), @@TRANCOUNT
--5a
--<blocked>
--6a
-- (excute next in b)
-- 7a
select '--7a: ' + cast(@@TRANCOUNT as varchar(10)), @@TRANCOUNT
if @@TRANCOUNT >0 rollback;
select '--7aa: ' + cast(@@TRANCOUNT as varchar(10)), @@TRANCOUNT
Code b:
--1b
use TSQL2012;
begin tran;
select '--1b: ' + cast(@@TRANCOUNT as varchar(10)), @@TRANCOUNT
--2b
--(excute next in a)
--3b
update Production.Suppliers
set fax= N'555-1216'
where supplierid= 1
select '--3b: ' + cast(@@TRANCOUNT as varchar(10)), @@TRANCOUNT
--4b
--(excute next in a)
--5b
update hr.Employees
set phone= N'555-9999'
where empid= 1;
select '--5b: ' + cast(@@TRANCOUNT as varchar(10)), @@TRANCOUNT
--6b
--<blocked>
--7b
select '--7b: ' + cast(@@TRANCOUNT as varchar(10)), @@TRANCOUNT
if @@TRANCOUNT >0 rollback;
select '--7bb: ' + cast(@@TRANCOUNT as varchar(10)), @@TRANCOUNT
Microsoft SQL ServerMicrosoft SQL Server 2008Microsoft SQL Server 2005
Last Comment
Vitor Montalvão
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ASKER
It seems 6b (<blocked>) per the book is not correct because there is no block at 6b.
6b is misleading, cause the b thread is already waiting in 5b. Here it wants to update Employees, but it is waiting, cause 2a has still its lock from its update.
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ASKER
Vitor,
re:> Because it's a deadlock and the engine already chose 'A' to be killed.
I am following the example in the book. Coming across to <blocked> at step 6b is expected per the book I am reading?
Is your conclusion "The book is wrong?"
If you find that the book is wrong, I am okay with that. But if you find the book is correct then my original question remain not answered (Why am I not coming across <blocked> at step 6b?)
re:> Because it's a deadlock and the engine already chose 'A' to be killed.
I am following the example in the book. Coming across to <blocked> at step 6b is expected per the book I am reading?
Is your conclusion "The book is wrong?"
If you find that the book is wrong, I am okay with that. But if you find the book is correct then my original question remain not answered (Why am I not coming across <blocked> at step 6b?)
Sorry, I was off on vacation.
The book is not wrong (at least if the table you post in your original question is from the book). Between points 6 and 7 it says:
"one transaction finnishes and the other transaction is aborted", so there's no human intervention, like I said before. Is the engine who chose which one to abort/kill.
The book is not wrong (at least if the table you post in your original question is from the book). Between points 6 and 7 it says:
"one transaction finnishes and the other transaction is aborted", so there's no human intervention, like I said before. Is the engine who chose which one to abort/kill.