oracle slides01 fp2005 ver 1.0

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Oracle - OS (LC)

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Oracle Architecture

Oracle Day 1

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ER/CORP/CRS/DB25/003 Version No.2.0

Objectives

 To Recall RDBMS concepts

 To introduce ORACLE and its products

 To introduce Oracle Client/Server Architecture

 To explain Oracle Physical structure-Data Files, Control Files,

Redo Files

 To explain Oracle Logical Structure- Tablespaces,

Segments, Extents, Blocks

 To introduce Schema objects-Tables, Sequences,

Synonyms, Views, Indexes and Clusters

 To explain Oracle Memory Structures and Background

Processes, Data Dictionary

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What is Oracle?

Oracle is a Relational Database Management System

• It is a management system which uses the Relational Data Model

• In the Relational Data Model, data is seen by the users in form of tables

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Database Servers

• Oracle 10g Database

• Oracle 9i Database

• Oracle 8i Database

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Application Development Tools

• Oracle Developer (Includes Forms, Reports, Graphics etc.)

• Oracle Designer

• Oracle Discoverer

• PL/SQL (Technology)

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Oracle Database Server

Oracle Database server:

– Is a database management system

that provides an open,

comprehensive, integrated approach

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Oracle Database Server Architecture

Control files Datafiles

Database

Redo Log files

Instance

SGA

Redo Log Buffer Shared Pool

Data Dictionary Cache

Library Cache

DBWR SMON

User process

Server process

PGA

Database Buffer Cache

Large Pool

Password file

Parameter file

Archived Log files

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Oracle Database

Oracle Database:

– Is a collection of data that is treated as a unit

– Consists of three file types

Control files

Datafiles

Redo Log files

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Oracle Instance

Oracle Instance:

• Is a means to access an Oracle database

• Always open one and only one database

• Consists of memory structures and background processes

Instance

SGA

Redo Log Buffer Shared Pool

Data Dictionary

Cache

Library Cache

DBWR SMON

Large Pool

Background Processes Memory structures

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Establishing a Connection

and Creating a Session

Connecting to an Oracle Instance:

– Establishing a user connection

– Creating a session

Session created

Database user

User process

Server process

Connection established

Oracle Server

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Oracle Database

Physical Structure

The physical structure includes three types of files:

• Control files, Data files, Redo log files.

Other key files:

• Parameter file

• Password file

• Archived redo log file

Passwordfile

Parameterfile

Archived Log files

Control files

Datafiles

Redo Log files

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Memory Structure

• Oracle’s memory structure consists of two memory areas known as:

– System Global Area (SGA): Allocated at instance startup, and is a fundamental component of an Oracle Instance

– Program Global Area (PGA): Allocated when the server process is started

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System Global Area

The SGA consists of several memory structures:

• Shared Pool

• Database Buffer Cache

• Redo Log Buffer

• Other structures (for example, lock and latch management, statistical data)

There are additional memory structures that can be configured within

the SGA:

• Large Pool

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Shared Pool

– Used to store:

• Most recently executed SQL statements

• Most recently used data definitions– It consists of two key performance-related memory structures:

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Library Cache

– Stores information about the most recently used SQL and PL/SQL statements

– Enables the sharing of commonly used statements

– Is managed by a least recently used (LRU) algorithm

– Consists of two structures:

• Shared SQL area

• Shared PL/SQL area– Size determined by the Shared Pool sizing

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Data Dictionary Cache

– A collection of the most recently used definitions in the database

– Includes information about database files, tables, indexes, columns, users, privileges, and other database objects– During the parse phase, the server process looks at the data dictionary for information to resolve object names and validate access

– Caching data dictionary information into memory improves response time on queries and DML

– Size determined by the Shared Pool sizing

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– Stores copies of data blocks that have been retrieved from the

datafiles– Enables great performance gains when you obtain and update data– Managed through the LRU algorithm

– DB_BLOCK_SIZE determines the block size

Database Buffer

Cache

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Redo Log Buffer

– Records all changes made to the database data blocks

– Primary purpose is recovery

– Changes recorded within are called redo entries

– Redo entries contain information to reconstruct or redo changes– Size defined by LOG_BUFFER

Redo Log Buffer

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Large Pool

– An optional area of memory in the SGA – Relieves the burden placed on the Shared Pool– Used for:

• Session memory (UGA) for the Shared Server

• I/O server processes

• Backup and restore operations or RMAN– Does not use an LRU list

– Sized by LARGE_POOL_SIZE

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Program Global Area

– Memory reserved for each user process

connecting to an Oracle database– Allocated when a process is created

– Deallocated when the process is terminated

– Used by only one process

User process

PGA Server

process

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Process Structure

Oracle takes advantage of various types of processes:

– User process: Started at the time a database user requests connection

to the Oracle server– Server process: Connects to the Oracle Instance and is started when a user establishes a session

– Background processes: Started when an Oracle Instance is started

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User Process

– A program that requests interaction with the Oracle server

– Must first establish a connection

– Does not interact directly with the Oracle server

Database user

Server process User

process

Connection established

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Server Process

– A program that directly interacts with the Oracle server

– Fulfills calls generated and returns results

– Can be Dedicated or Shared Server

Connection established Session created

Database user

User process

Server process

Oracle server

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Database Writer (DBWn)

• DBWn writes when:

– Checkpoint occurs– Dirty buffers reach threshold

– There are no free buffers– Timeout occurs

– Tablespace OFFLINE– Tablespace READ ONLY– Table DROP or

TRUNCATE

Instance SGA

Control files

Datafiles Redo Log

files Database

DBWn

Database Buffer Cache

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Log Writer (LGWR)

• LGWR writes:

– At commit – When one-third full– When there is 1 MB of redo

– Every three seconds– Before DBWn writes

Instance SGA

Control files

files

Database

Redo Log Buffer

DBWn LGWR

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System Monitor (SMON)

Control files

files

Database

InstanceSGA

SMON

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Process Monitor (PMON)

• Cleans up after failed processes by:

– Rolling back the transaction

– Releasing locks– Releasing other resources– Restarting dead

dispatchers

PGA area

Instance SGA

PMON

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Checkpoint (CKPT)

• Responsible for:

– Signaling DBWn at checkpoints

– Updating datafile headers with checkpoint

information – Updating control files with checkpoint information

Control files

files

Database

Instance SGA

DBWn LGWR CKPT

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Archiver (ARCn)

– Optional background process

– Automatically archives online redo logs when ARCHIVELOG mode is set– Preserves the record of all changes made to the database

ARCn

Archived Redo Log files

Control files Datafiles Redo Log

files

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Control File

– A small binary file

– Defines current state of physical database

– Maintains integrity of database

– Required:

• At MOUNT state during database startup

• To operate the database– Linked to a single database

– Loss may require recovery

– Sized initially by

CREATE DATABASE

Control files Database

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Control File Contents

• A control file contains the following entries:

– Database name and identifier– Time stamp of database creation– Tablespace names

– Names and locations of datafiles and redo log files– Current redo log file sequence number

– Checkpoint information– Begin and end of undo segments– Redo log archive information

– Backup information

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Redo Log Files

Redo log files have the following characteristics:

– Record all changes made to data

– Provide a recovery mechanism

– Can be organized into groups

– At least two groups required

Redo Log files

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Structure of Redo Log Files

Member

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How Redo Log Files Work

– Redo log files are used in a cyclic fashion

– When a redo log file is full, LGWR will move to the next log group

• Called a log switch

• Checkpoint operation also occurs

• Information written to the control file

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Archived Redo Log Files

– Filled online redo log files can be archived

– There are two advantages in running the database in ARCHIVELOG mode and archiving redo log files:

• Recovery: A database backup together with online and archived redo log files can guarantee recovery of all committed

transactions

• Backup: This can be performed while the database is open

– By default, database is created in NOARCHIVELOG mode

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Archived Redo Log Files

– Accomplished automatically by ARCn– Accomplished manually through SQL statements– When successfully archived:

• An entry in the control file is made

• Records: archive log name, log sequence number, and high and low system change number (SCN)

• Filled redo log file cannot be reused until:

– A checkpoint has taken place – File has been archived by ARCn

– Can be multiplexed– Maintained by the DBA

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Logical Structure

– Dictates how the physical space of a database is used

– Hierarchy consisting of tablespaces, segments, extents, and blocks

Tablespace

Datafile Segment

Blocks Extent

Segment

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Tablespaces and Datafiles

• Oracle stores data logically in tablespaces and physically in datafiles.

– Tablespaces:

• Can belong to only one database at a time

• Consist of one or more datafiles

• Are further divided into logical units of storage – Datafiles:

• Can belong to only one tablespace and one database

• Are a repository for schema object data

Database Tablespace Datafiles

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Types of Tablespaces

– SYSTEM tablespace

• Created with the database

• Contains the data dictionary

• Contains the SYSTEM undo segment– Non-SYSTEM tablespace

• Separate segments

• Eases space administration

• Controls amount of space allocated to a user

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Creating Tablespaces

CREATE TABLESPACE userdata

DATAFILE '/ora/data01.dbf' SIZE 50M

AUTOEXTEND ON NEXT 5M MAXSIZE 200M;

• A tablespace is created using the command:

• CREATE TABLESPACE

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Dropping Tablespaces

– Cannot drop a tablespace if it:

• Is the SYSTEM tablespace

• Has active segments– INCLUDING CONTENTS drops the segments

– INCLUDING CONTENTS AND DATAFILES deletes datafiles

– CASCADE CONSTRAINTS drops all referential integrity constraints

DROP TABLESPACE userdata

INCLUDING CONTENTS AND DATAFILES;

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Obtaining Tablespace Information

• Obtaining tablespace and datafile information can be obtained by querying the following:

– Tablespaces:

• DBA_TABLESPACES– Datafile information:

• DBA_DATA_FILES

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Rollback Segments: Purpose

Transaction rollback

Transaction recovery

Rollback segment

Read consistency

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Read Consistency

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Types of Rollback Segments

– SYSTEM: Used for objects in the SYSTEM tablespace

– Non-SYSTEM: Used for objects in other tablespaces:

– Private: Acquired by a single instance– Public: Acquired by any instance

– Deferred: Used when tablespaces are taken offline immediate, temporary, or for recovery

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Extent Allocation and Deallocation

– An extent is a chunk of space used by a segment within a tablespace

– An extent is allocated when the segment is:

• Created

• Extended

• Altered– An extent is deallocated when the segment is:

• Dropped

• Altered

• Truncated

Tiêu đề	Oracle Architecture
Trường học	Infosys Technologies Ltd
Thể loại	lecture notes
Năm xuất bản	2005

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Số trang	78
Dung lượng	0,94 MB