UNIDAD 3 Transacciones Ing

1UNIDAD III

TRANSACCIONES EN LAS BASES DE DATOS

UNIVERSIDAD TECNOLOGICA DE NEZAHUALCOYOTL

Divisin de Informtica y Computacin

Ingeniera en Tecnologas de informacin

Academia de Bases de Datos

DESARROLLADO POR: Lic. PABLO JULIO GUTIRREZ ALARCN

UTNeza Acad. BD Base de Datos para Aplicaciones - PJGA 2

Contenido

Procesamiento de Transacciones. Conceptos de transacciones. Propiedades de las Transacciones. Planes y recuperabilidad. Seriabilidad de los Planes. Transacciones en SQL.

2UTNeza Acad. BD Base de Datos para Aplicaciones - PJGA 3

Procesamiento de Transacciones.

La Administracin de las Transacciones tiene como objetivo llevar el control para la recuperacin y la concurrencia que

estn relacionadas con la cuestin general de la proteccin de los datos; es decir, la proteccin contra la prdida o dao de la informacin que est en la base de datos. En particular tienen

que ver con problemas como:El sistema puede abortar cuando estn ejecutando algn programa, con lo que dejara a la BD en un estado desconocido.Dos programas que estn ejecutndose al mismo tiempo (en forma concurrente) pueden interferir entre s y en consecuencia, producir resultados incorrectos, ya sea dentro de la BD o fuera de ella.


Conceptos de transacciones

Una transaccin en una unidad de trabajo lgica. Considerndose como unidad lgica : Insert, delete, update a una tabla de la base de datos. C.J. Date Inrtoduccin a los sistemas de BD

Una transaccin es una unidad de la ejecucin de un programa que accede y posiblemente actualiza varios elementos de datos. Una transaccin se inicia por la ejecucin de un programa de usuario, escrito en lenguaje de manipulacin de datos de alto nivel o en un lenguaje de programacin. korth-Silberschatz-Sudarshan Fundamentos de BD

Una Transaccin es un conjunto de operaciones que van a ser tratadas como una nica unidad. Estas transacciones deben cumplir 4 propiedades fundamentales comnmente conocidas como ACID Atomicidad, Consistencia, Aislamiento y Durabilidad (Atomicity, Consistency, Isolation, Durability). Christian Crovetto Huerta Oracle 10g B.D


Propiedades de las transacciones


Database

Redolog files

Control files

Data files

Userprocess

Serverprocess

PGA

Archived log files

Parameterfile

Passwordfile

Instance

SGA

Redo logbuffer

Data buffercache

Shared pool

Data dict.cache

Librarycache

PMONDBW0SMON LGWRCKPT Others

Overview


Estados de una transaccin1

2 3

4 5


Bitcora de transacciones


Recuperacin de transacciones


Database Transactions

A database transaction consists of one of the following: DML statements which constitute one consistent change to

the data One DDL statement One DCL statement


Transacciones en SQL


Database Transactions

Begin when the first DML SQL statement is executed End with one of the following events:

A COMMIT or ROLLBACK statement is issued A DDL or DCL statement executes (automatic commit) The user exits iSQL*Plus The system crashes


With COMMIT and ROLLBACK statements, you can: Ensure data consistency Preview data changes before making changes permanent Group logically related operations

Advantages of COMMITand ROLLBACK Statements


SAVEPOINT B

SAVEPOINT A

DELETE

INSERT

UPDATE

INSERT

COMMITTime

Transaction

ROLLBACK to SAVEPOINT B

ROLLBACK to SAVEPOINT A

ROLLBACK

Controlling Transactions


SGA

Redo logbuffer

Data buffercache

Shared pool

LGWR

Instance

Database

Redolog files

Control files

Data files

1

23

4

Userprocess

Serverprocess

COMMIT Processing


UPDATE...SAVEPOINT update_done;Savepoint created.INSERT...ROLLBACK TO update_done;Rollback complete.

Create a marker in a current transaction by using the SAVEPOINT statement.

Roll back to that marker by using the ROLLBACK TOSAVEPOINT statement.

Rolling Back Changes to a Marker


DML statement

Old image

New image

Rollback segment

Table

Rollback Segment


An automatic commit occurs under the following circumstances: DDL statement is issued DCL statement is issued Normal exit from iSQL*Plus, without explicitly issuing COMMIT or ROLLBACK statements

An automatic rollback occurs under an abnormal termination of iSQL*Plus or a system failure.

Implicit Transaction Processing

10


The previous state of the data can be recovered. The current user can review the results of the DML operations by

using the SELECT statement. Other users cannot view the results of the DML statements by the

current user. The affected rows are locked; other users cannot change the data

within the affected rows.

State of the Data Before COMMIT or ROLLBACK


Data changes are made permanent in the database. The previous state of the data is permanently lost. All users can view the results. Locks on the affected rows are released; those rows are

available for other users to manipulate. All savepoints are erased.

State of the Data after COMMIT

11


COMMIT;Commit complete.

Make the changes.

Commit the changes.

DELETE FROM employeesWHERE employee_id = 99999;1 row deleted.

INSERT INTO departments VALUES (290, 'Corporate Tax', NULL, 1700);1 row inserted.

Committing Data


Discard all pending changes by using the ROLLBACKstatement: Data changes are undone. Previous state of the data is restored. Locks on the affected rows are released.

DELETE FROM copy_emp;22 rows deleted.ROLLBACK;Rollback complete.

State of the Data After ROLLBACK

12


If a single DML statement fails during execution, only that statement is rolled back.

The Oracle server implements an implicit savepoint. All other changes are retained. The user should terminate transactions explicitly by

executing a COMMIT or ROLLBACK statement.

Statement-Level Rollback


Read consistency guarantees a consistent view of the data at all times.

Changes made by one user do not conflict with changes made by another user.

Read consistency ensures that on the same data: Readers do not wait for writers. Writers do not wait for readers.

Read Consistency

13


SELECT *FROM userA.employees;

UPDATE employeesSET salary = 7000WHERE last_name = 'Goyal';

Datablocks

Rollbacksegments

changedand unchanged databefore changeold data

User A

User B

Readconsistentimage

Implementation of Read Consistency


Output Time Session 1 Session 2

t1

t2

t3

t4

t5

SELECT salary FROM employeesWHERE last_name='King';24000

UPDATE employeesSET salary=salary+10000WHERE last_name='King';

24000

COMMIT;

34000

SELECT salary FROM employeesWHERE last_name='King';

SELECT salary FROM employeesWHERE last_name='King';

Read Consistency Example

14


In an Oracle database, locks: Prevent destructive interaction between concurrent

transactions Require no user action Automatically use the lowest level of restrictiveness Are held for the duration of the transaction Are of two types: explicit locking and implicit locking

Locking


Two lock modes: Exclusive: Locks out other users Share: Allows other users to access

High level of data concurrency: DML: Table share, row exclusive Queries: No locks required DDL: Protects object definitions

Locks held until commit or rollback

Implicit Locking

15


Bibliografia Date C. J. SISTEMAS DE BASES DE DATOS (VOLUMEN I). Quinta Edicin. Addison Wesley. Shkuntala Atre. TCNICAS DE BASES DE DATOS. ESTRUCTURACIN EN DISEO Y ADMINISTRACIN. Trillas, 1991. Nelson T. Dinerstein. SISTEMAS DE MANEJOS DE ARCHIVOS Y BASES DE DATOS PARA MICROCOMPUTADORAS. CECSA, 1990. Rose Deakin. BASES DE DATOS. USO Y ADMINISTRACIN EN CENTROS DE COMPUTO. Trillas, 1988. Korth., Silberschatz, Sudarshan FUNDAMENTOS DE BASES DE DATOS.01 McGrawHill, 4ta. Edicin, Mexico, 2002 Adad Ruben, Medina Miguel A. y Careaga Alfredo. FUNDAMENTOS DE LAS ESTRUCTURAS DE DATOS RELACIONALES. Megabyte. Noriega Editores, 1992. Cesar Perez Lopez ORACLE 9I, ADMINISTRACIN Y ANLISIS DE BASE DE DATOS Ed. Alfaomega RaMa, Mxico, 2003 Cesar Perez Lopez ORACLE 9I / SERVIDOR DE APLICACIONES RED Y PROGRAMACION Ed. Alfaomega RaMa, Mxico, 2003

Michael Abbey, Mike Corey, Ian Abramson ORACLE 9i , GUIA DE APRENDISAJE Mc Graw Hill- Osborne, Oracle Press, Mexico, 2002 Javier Lopez H. ORACLE, FUNDAMENTOS PARA EL DESARROLLO DE APLICACIONES WEB Coleccin USERS-libros.tectimes.com MP Ediciones Bs. As.-Argentina Paul Dorsey, Joseph R. Hudicka ORACLE 8, DISEO DE BASES DE DATOS CON UML Oracle Press- McGrawHill, Mexico, 1999

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