So, after some time, You will notice that one of the transactions was completed successfully while the other transaction is chosen as the deadlock victim by giving the following error. In this situation, neither of the transactions can move forward. After 15 seconds, Transaction 1 wants to acquire a lock on TableB which is already acquired by Transaction 2 and at the same time, Transaction 2 wants to acquire a lock on TableA which is already acquired by Transaction 1. Once Transaction 1 starts its execution, it acquires a lock on TableA and then waits for 15 seconds, At the same time, Transaction 2 starts its execution, it acquires a lock on TableB and then waits for 15 seconds.
Sql server deadlock solution code#
Now, first, execute the Transaction 1 code and then immediately execute the Transaction 2 code.
Sql server deadlock solution update#
UPDATE TableA SET Name = 'Anurag From Transaction2' WHERE Id = 101 UPDATE TableB SET Name = 'Priyanka From Transaction2' WHERE Id = 1001 Then intentionally we delayed the transaction execution for 15 seconds by using WAITFOR DELAY ’00:00:15′ statement and then we try to execute the second update statement i.e. The transaction will start its execution and will execute the first update statement i.e. In between the first and second update statements, we have delayed the transaction execution for 15 seconds. UPDATE TableB SET Name = 'Priyanka From Transaction1' WHERE Id = 1001Īs you can see in the below code, here we have also written the transaction with two update statements. UPDATE TableA SET Name = 'Anurag From Transaction1' WHERE Id = 101 In between the first and second update statements, we have delayed the execution for 15 seconds. Transaction 1 Code:Īs you can see in the below code, here we have written the transaction with two update statements. From the first instance execute Transaction 1 code and from the second instance execute Transaction 2 code. Open 2 instances of SQL Server Management Studio. The following 2 transactions will result in a deadlock situation. INSERT INTO TableB values (1003, 'Preety') INSERT INTO TableB values (1002, 'Dewagan') INSERT INTO TableB values (1001, 'Priyanka') INSERT INTO TableA values (105, 'Sambit') INSERT INTO TableA values (103, 'Pranaya') INSERT INTO TableA values (102, 'Mohanty') INSERT INTO TableA values (101, 'Anurag') Please use the below SQL Script to create and populate the tables with the sample data. We are going to use the following two tables to understand deadlock. Let us understand the Deadlock in SQL Server with Examples. Understanding Deadlock in SQL Server with Examples. The process that is chosen as the deadlock victim will give the following error. As a result, other processes can move forward. When deadlocks occur in SQL Server, then SQL Server chooses one of the processes (transactions) as the deadlock victim and then rolls back that process.
In such cases, neither of the transactions (processes) can move forward resulting in a deadlock. At the same time, Process B needs the resource Table A which is already locked by Process A. Now to complete its execution, process A needs the resource Table B which is already locked by Process B. Process A started and it acquires a lock on table A and in the meantime, Process B started and it acquired a lock on Table B.
We have two tables such as Table A and Table B in the database. when a deadlock occurs in a database.Īs shown in the above diagram, we have two processes (process means transactions) such as Process A and Process B. If you are confused, then just have a look at the following diagram which explains the above points i.e. In such cases, neither of the processes can move forward, as each process is waiting for the other process to release the lock resulting in a deadlock in SQL Server. When a deadlock occurs in SQL Server?Ī deadlock occurs in a database when two or more processes have already a resource locked, and then each process wants to acquire a lock on the resource that the other process has already locked. Before going to understand what is Deadlock in SQL Server, let’s first discuss when a deadlock occurs in SQL Server. Please read our previous article where we discussed Concurrency Problems in SQL Server with examples. In this article, I am going to discuss Deadlock in SQL Server with examples.
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