Svetlin Nakov - Database Transactions

Database Transactions and Transaction Management Svetlin Nakov National Academy for Software Development academy.devbg.org

Agenda ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Agenda (2) ,[object Object],[object Object],[object Object]

Transactions ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

A Transaction Rollback Commit Read Write Write Durable starting state Durable, consistent, ending state Collection of reads and writes

Transactions Behavior ,[object Object],[object Object],[object Object],[object Object],[object Object]

Transactions: Examples ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Transfer $100

What Can Go Wrong? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Transactions Properties ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Atomicity ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Consistency ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Isolation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Durability ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

ACID Transactions and RDBMS Servers ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Scheduling Transactions ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Serial Schedule – Example ,[object Object],[object Object],[object Object],Time Trans. Step Value 6 T 2 Write balance 125 5 T 2 4 T 2 Read balance 150 3 T 1 Write balance 150 2 T 1 balance = 100 + 50 1 T 1 Read balance 100 balance = 150 - 25

Serializable Transactions ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Concurrency Problems ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Concurrency Problems (2) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Dirty Read (Read Uncommitted) – Example T2 writes incorrect balance ,[object Object],Time Trans. Step Value 6 T 1 Rollback 125 5 T 2 4 T 2 Read balance 3 T 1 2 T 1 1 T 1 Read balance 100 balance = 150 - 25 150 balance = 100 + 50 Write balance 1 5 0 7 T 2 Write balance Uncommitted Undoes T1

Lost Update – Example Lost update!! ,[object Object],Time Trans. Step Value 6 T 2 Write balance 7 5 5 T 1 4 T 2 balance = balance - 25 3 T 1 balance = balance + 50 2 T 2 Read balance 1 T 1 Read balance 100 Write balance 100 150

Concurrency Control Techniques

Concurrency Control ,[object Object],[object Object],[object Object],[object Object],[object Object]

Concurrency Control Techniques ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Locking ,[object Object],[object Object],[object Object],[object Object],[object Object]

Timestamping ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Locking Strategies ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Optimistic Locking ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Optimistic Locking Phases ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Pessimistic Locking ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Locking – Basic Rules ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Deadlock ,[object Object],[object Object],[object Object],[object Object]

Dealing with Deadlock ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Lock Management ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Locking Granularity ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Coarse vs. Fine Granularity ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Transactions and Recovery ,[object Object],[object Object],[object Object],[object Object],[object Object]

Crash Before Completion – Sample Scenario ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Recovery from Crash ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Creating REDO Log ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Recovering From a Crash ,[object Object],[object Object],[object Object],[object Object],[object Object]

Transactions and SQL ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Transactions in SQL Server: Example ,[object Object],[object Object],CREATE TABLE ACCOUNT ( id int NOT NULL, balance decimal NOT NULL) CREATE OR REPLACE PROCEDURE sp_Transfer_Funds( from_account IN INT, to_account IN INT, ammount IN NUMBER ) IS BEGIN BEGIN TRAN ( example continues )

Transactions in SQL Server: Example (2) UPDATE ACCOUNT set balance = balance - ammount WHERE id = from_account; IF SQL%ROWCOUNT <> 1 THEN ROLLBACK; RAISE_APPLICATION_ERROR(-20001, 'Invalid src account!'); END IF; UPDATE ACCOUNT set balance = balance + ammount WHERE id = to_account; IF SQL%ROWCOUNT <> 1 THEN ROLLBACK; RAISE_APPLICATION_ERROR(-20002, 'Invalid dst account!'); END IF; COMMIT; END;

Transactions and isolation ,[object Object],[object Object],yes no no Repeatable read yes yes no Read committed no yes Dirty reads no yes Repeatable reads no yes Phantom reads Serializable Read uncommitted Level of isolation

Isolation levels ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Isolation levels ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

When and How to Use Transactions?

Transactions Usage ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Transactions Usage – Examples ,[object Object],[object Object],[object Object],[object Object],[object Object]

Database Transactions and Transaction Management Questions ?

Svetlin Nakov - Database Transactions

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