Batches, Transactions, & Errors John Deardurff Website: http://john.deardurff.com Twitter: @John_Deardurff Email: John@Deardurff.com December 12, 2015

Presentation Topics How Queries are Processed Types of Errors Working with Batches ACID Transactions Explicit Transactions Error Handling

Parse Resolve Optimize Compile Execute Execute SQL Sets Ad Hoc Query Stored Procedure Syntax Parse Execution Context Resolve Compile Optimize Execution Plan Procedure Cache Compile Run Time Execute Execute SQL Sets

Working with Batches

VS Batches vs. Transactions Batches Transactions TSQL2012.mdf Sends Code to the Processor Sends Data to the Database

Batches And Variables First Batch Successful Second Batch Fails

Transactions must pass the ACID test Atomicity – All or Nothing Consistent – Only valid data Isolated – No interference Durable – Data is recoverable

Transaction Recovery Transaction Recovery Action Required 1 None 2 Roll forward 3 Roll back 4 Roll forward 5 Roll back Checkpoint System Failure

Auto Commit Transactions without Error Handling TSQL2012.ldf Checkpoint TSQL2012.mdf

Explicit Transactions without Error Handling TSQL2012.ldf Checkpoint TSQL2012.mdf

Explicit Transactions with Error Handling TSQL2012.ldf TSQL2012.mdf Checkpoint

What are Locks? Transaction 1 Transaction 2 TSQL2012.mdf

Module 13: Creating Highly Concurrent SQL Server 2012 Applications Course 10776A What Problems does Locking Prevent? Module 13: Creating Highly Concurrent SQL Server 2012 Applications Lost Updates Uncommitted dependency (dirty read) Inconsistent analysis (non-repeatable reads) Phantom reads Question: Has your organization experienced concurrency problems with database applications? If so, what behavior did you see? Answer: Answers will vary. References: Concurrency Problems: http://go.microsoft.com/fwlink/?LinkID=233921 Concurrency Effects: http://go.microsoft.com/fwlink/?LinkID=233922 Locking in the Database Engine: http://go.microsoft.com/fwlink/?LinkID=233923

Lost Update Original value of 125. The second session is unaware of the first sessions update.

Uncommitted dependency (dirty read) Clean Read Dirty Read

Inconsistent analysis (non-repeatable read) Change Isolation Level to Repeatable Read

Phantom Reads – (Demo Setup) Added 3 columns for demo

Phantom Reads Missing record 18

Transaction Isolation Levels

Module 13: Creating Highly Concurrent SQL Server 2012 Applications Course 10776A Transaction Isolation Levels Module 13: Creating Highly Concurrent SQL Server 2012 Applications Isolation Level Dirty Read Lost Update Nonrepeatable Read Phantoms Read uncommitted Yes Read committed (default) No Repeatable read Serializable Snapshot Discuss the effects that each of the transaction isolation levels has on data access. Be sure that students understand the READ COMMITTED isolation level, and that it is the default transaction isolation level. References: SET TRANSACTION ISOLATION LEVEL (Transact-SQL): http://go.microsoft.com/fwlink/?LinkID=233927 Transaction Isolation Levels: http://go.microsoft.com/fwlink/?LinkID=209385