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Concurrency Control/SQL - AnomalyBank - 02 - Transaction W.sql

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+-- This Script is part of the AnomalyBank Series
+--
+-- Problem: Inconsistent retrieval
+--
+-- Revision History
+-- 2019.04.09 Karsten Jeppesen (kaje@ucn.dk) initial push
+-- 2020.03.30 Karsten Jeppesen (kaje@ucn.dk) Spellcheck
+--
+-- Anomaly: Inconsistent retrieval
+--
+-- PreReq: SQL - AnomalyBank - 01 - Initialize Bank
+--
+-- Distributed Systems, Concepts and Design, page 684, Figure 16.6
+-- The Inconsistent Retrievals Problem, Transaction W
+-- Start this script no later than 5 secs after Transaction V
+-- +------------------------------+------------------------------------+
+-- |      Transaction V           |     Transaction W                  |
+-- +------------------------------+------------------------------------+
+-- | a.withdraw(100);    100      |                                    |
+-- |                              | total = a.getBalance( )        100 |
+-- |                              | total = total + b.getBalance() 300 |
+-- |                              | total = total + c.getBalance() 500 |
+-- | b.deposit(100)      200      |                                    |
+-- +------------------------------+------------------------------------+
+--
+-- The Correct Branch balance is 600 NOT 500
+--
+-- EXERCISE: Try the different ISOLATION levels.
+-- SET TRANSACTION ISOLATION LEVEL
+--     { READ UNCOMMITTED
+--     | READ COMMITTED
+--     | REPEATABLE READ
+--     | SNAPSHOT
+--     | SERIALIZABLE
+--     }
+
+
+USE AnomalyBank
+-- CHOOSE ONE OF THE FOLLOWING BY UNCOMMENTING
+--SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
+--SET TRANSACTION ISOLATION LEVEL READ COMMITTED
+--SET TRANSACTION ISOLATION LEVEL REPEATABLE READ
+--SET TRANSACTION ISOLATION LEVEL SNAPSHOT
+--SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
+
+-- Nothing to initialize
+
+-- And here comes The Inconsistent Retrievals Problem
+
+DECLARE @Balance int
+DECLARE @Total int
+DECLARE @Done int = 0;
+DECLARE @DeadlockErr int = 1205;
+DECLARE @LockTimeout int = 1222;
+
+WHILE @Done = 0
+BEGIN
+	PRINT 'Branch totalling start';
+	BEGIN TRANSACTION T1 WITH MARK N'Branch Total';
+	BEGIN TRY
+		SET @Total = 0;
+		-- total = a.getBalance( )
+		SELECT @Balance=Balance FROM Accounts WHERE Customer='a';
+		SET @Total = @Total + @Balance;
+		-- total = total + b.getBalance()
+		SELECT @Balance=Balance FROM Accounts WHERE Customer='b';
+		SET @Total = @Total + @Balance;
+		-- total = total + c.getBalance()
+		SELECT @Balance=Balance FROM Accounts WHERE Customer='c';
+		SET @Total = @Total + @Balance;
+		PRINT N'Total balance is';
+		PRINT @Total;
+		SET @Done = 1;
+		COMMIT TRANSACTION T1;
+	END TRY
+	BEGIN CATCH
+		if (ERROR_NUMBER() = @DeadlockErr)
+		BEGIN
+			PRINT 'ABORTED BY DEADLOCK';
+			ROLLBACK;
+			CONTINUE;
+		END
+		if (ERROR_NUMBER() = @LockTimeout)
+		BEGIN
+			PRINT 'ABORTED BY LOCK TIMEOUT';
+			ROLLBACK;
+			CONTINUE;
+		END
+		SELECT 'ABORTED BY UNHANDLED ERROR';
+		SET @Done = 1;
+	END CATCH
+END
+
+
+
+
+
+
+
+
+
+select * FROM Accounts
+USE master