02_DB Architecture Overview.ppt

8/11/2019 02_DB Architecture Overview.ppt

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Database Architecture Overview


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Oracle Instance

Oracle Database

Database Files

Server Processes Memory Structures

Transactions

Data Dictionary

Schema And Users

Oracle 11g Server Architecture


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Oracle Server Architecture

An Oracle server: Is a database management

system that provides an

open, comprehensive,

integrated approach toinformation management

Consists of an Oracle

instance and an Oracle

database

Oracle Server


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Overview of Primary Components

Instance

SGA

Redo log

buffer cache

Shared pool

Data Dict.

cache

Library

cache

DBWRSMONPMON CKPTLGWR Others

Userprocess

Server

process

PGA

Controlfiles

Datafiles Archived

log filesParameter

file

Password

file

Redo logfiles

Database

Database

buffer cache


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Oracle Instance

Oracle Database

Database Files


Data Dictionary

Schema And Users



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Oracle Instance

Is a means to access an Oracle database

Always opens one and only one database

Consists of memory and process structures

Background

structures

Memory

structures

SGA

Redo logbuffer cache

Databasebuffer cache

Shared pool

DBWRSMONPMON CKPTLGWR Others

Data Dictionary

cache

Library

cache

Instance


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Oracle Instance

Oracle Database

Database Files


Data Dictionary

Schema And Users



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Physical Structure

The physical structure of an Oracle database isdetermined by the operating system files that

provide the actual physical storage for database

information.

Control files

Data files

Redo log files Controlfiles

Data files

(includes

datadictionary)

Header

Online

redo log

files)


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Oracle Instance

Oracle Database

Database Files


Data Dictionary

Schema And Users



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Parameter Files

Control Files

Data Files

Redo Log Files Undo Data Files

Database Files


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Oracle Database

Controlfiles

Datafiles Archived

log filesParameter

file

Password

file

Redolog files

Oracle Database


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Parameter Files

Control Files

Data Files


Database Files


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Parameter Files

Entries are specific to the instance being accessed

There are two kinds of parameters:

Explicit: Having an entry in the file

Implicit: No entry within the file, but assuming the Oracle

default values

Multiple files can be used for a single database to

optimize performance in different situations.


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Parameter Files

Control Files

Data Files


Database Files


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Control FileThe control file is a binary file that defines the

current state of the physical database.. Loss of the control file requires recovery

Is read at MOUNTstage

Is required to operate

Is linked to a single database Should be multiplexed

Maintains integrity of database

Sized initially by

CREATE DATABASE

Controlfiles

Database


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Parameter Files

Control Files

Data Files


Database Files


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Parameter Files

Control Files Data Files

Tablespaces

Oracle Managed Files

Data Block

Data Types

Tables

Indexes Redo Log Files

Undo Data Files

Database Files


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Logical Structure

The logical structure of the Oracle architecturedictates how the physical space of a database is to be used.

A hierarchy exists in this structure that consists of

tablespaces, segments, extents, and blocks.

Tablespace

Data file

Segment

BlocksExtent

Segment


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SYSTEMand Non-SYSTEMTablespaces

SYSTEMtablespace:

Created with the database

Contains the data dictionary

Contains the SYSTEMundo segment

Non-SYSTEMtablespaces:

Separate segments

Ease space administration

Control amount of space allocated to a user


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Parameter Files

Control Files

Data Files

Tablespaces


Data Block Data Types

Tables


Undo Data Files

Database Files


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Oracle Managed Files (OMF) simplify file

administration by eliminating the need to directly

manage the files in an Oracle database

This feature has two major thrusts: Allows database objects to be created without

specifying the underlying operating system files

Automatically removes obsolete data files and online

redo logs


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Parameter Files


Tablespaces


Data Block

Data Types Tables


Undo Data Files

Database Files


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Database Block

Minimum unit of I/O

Consists of one or more OS blocks

Set at tablespace creation

DB_BLOCK_SIZEis the default block size


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Parameter Files

Control Files

Data Files

Tablespaces


Data Block

Data Types Tables


Undo Data Files

Database Files


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Oracle data types

CHAR(N), NCHAR(N)

VARCHAR2(N),

NVARCHAR2(N)

NUMBER(P,S)

DATE

RAW(N)BLOB, CLOB,

NCLOB, BFILE

LONG, LONG RAW

ROWID

VARRAY

TABLE

REF

Data type

Built-inUser-defined

Scalar RelationshipCollection


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System-Provided Datatypes

Built-In Datatype

CHARACTER

DATE

NUMBER

LOB

RAW

ROWID

Native Datatypes

ANSI

DB2

SQL/DS

Support Datatypes

PL/SQL Datatypes

BOOLEAN

BINARY_INTEGER

Extended Datatypes

Text

Image

Video

Audio

Spatial

XML

Time Series


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Parameter Files

Control Files

Data Files

Tablespaces


Data Block

Data Types

Tables


Undo Data Files

Database Files


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Tables in Oracle

Regular table

Cluster

Partitionedtable

Index-organized

table


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Parameter Files


Tablespaces


Data Block Data Types

Tables


Undo Data Files

Database Files


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Classification of Indexes

Logical Single column or concatenated

Unique or nonunique

Function Based

Domain Based

Physical

Partitioned or nonpartitioned

B-tree

Normal or reverse key

Bitmap

Bitmap Join Index


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Parameter Files

Control Files

Data Files


Database Files


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Using Redo Log Files

Redo log files record all changes made to data and

provide a recovery mechanism from a system or

media failure.

Redo log files are organized into groups.

An Oracle database requires at least two groups.

Each redo log within a group is

called a member.

Redolog files

Database


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Structure of Redo Log Files

Group 2 Group 3Group 1

Member

Disk 1

Disk 2Member

Member Member

MemberMember


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How Redo Logs Work

Redo logs are used in a cyclic fashion.

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

next log group.

This is called a log switch Checkpoint operation also occurs

Information is written to the control file


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Parameter Files

Control Files

Data Files


Database Files


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Undo Data Overview

Before Oracle makes a change to a database

block it is copied to the Undo area.

Used for Rollback and Read Consistency.


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Oracle Instance

Oracle Database

Database Files


Transactions

Data Dictionary

Schema And Users



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Process Structure

An Oracle process is a program that depending on itstype can request information, execute a series ofsteps, or perform a specific task.On some OS (MS Windows) these are actually implemented as

process threads.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 startedwhen a user establishes a session.

Background process: Available when an Oracle instance isstarted


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Background Processes

The relationship between the physical and memory

structures is maintained and enforced by Oracles

background processes.

Mandatory background processes

DBWn PMON CKPT

LGWR SMON and others

Optional background processesARCn LMON Snnn

QMNn LMDn RECO

CJQ0 Pnnn and others

LCKn Dnnn


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Oracle Instance

Oracle Database

Database Files


Transactions

Data Dictionary

Schema And Users



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Memory Structure

Oracles 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 (SGA)

The SGA consists of several memory structures:

Shared pool

Database buffer cache

Redo log buffer Other structures (e.g. lock and latch

management, statistical data)


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System Global Area (SGA)

SGA is dynamic and sized using MEMORY_TARGETwithoutshutting down the instance

SGA memory allocated and tracked in granules by SGAcomponents

Contiguous virtual memory allocation

Size based on MEMORY_TARGET


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Program Global Area (PGA)

The PGA is memory reserved for each user process

that connects to an Oracle database.Managed as part of the MEMORY_TARGET

User

process

Stackspace

Sessioninformation

sort area, cursorinformation

SGA

Shared SQL areas

SGA

Sessioninformation

PGA Dedicated server Shared server

Serverprocess

Shared SQL areas

Stackspace

sort area, cursorinformation


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Oracle Instance

Oracle Database

Database Files


Transactions

Data Dictionary

Schema And Users



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Transactions

Oracle has an implicit transaction model.

A transaction starts immediately after the last one

completes

Can be made READ-ONLY via ALTER

TRANSACTION command

COMMIT or ROLLBACK ends transaction


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Oracles Multi-Version ConcurrencyRead Consistent Row Locking

With Oracle report

update UndoTablespace

BeforeImage

accuratereport

Budget Table Updates dont lockout reports and

reports dont lockout updates

Reports see only committed datavia Multi-Versioning

Queries yield maximumthroughput with correct results -no waiting and no dirty reads!

Row locks never escalate - themost scaleable solution available


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Multi Version Read Consistency High

Throughput Concurrency

Performance Table stakes Oracle Microsoft Sybase

Unique Concurrency Model Yes No No

Readers Dont Block Writers Yes No* No

Writers Dont Block Readers Yes No* No

Guarantees Consistent Queries Yes Yes No

Eliminates Lock Escalation Yes No No

Reduces Deadlocks under Load Yes No No

Oracle does not compromise data accuracy for greater concurrency*Except when using Snapshots in SS 2005


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Oracle Instance

Oracle Database

Database Files


Transactions

Data Dictionary

Schema And Users



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Data Dictionary

During database creation, the Oracle server createsadditional object structures within the data files.

Data dictionary tables

Dynamic performance tables

Controlfiles

Datafiles

Redologfiles

Database

Data Dictionary Tables

Dynamic Performance Tables

D t Di ti


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Data Dictionary

The data dictionary is a set of read-only tables and

views that record, verify, and provide information

about its associated database.

Describes the database and its objects

Includes two types of objects:

Base tables Store description of database

Created with CREATE DATABASE

Data Dictionary views

Summarize base table information

Created using catalog.sqlscript


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Data Dictionary Contents

The data dictionary provides information about:

Logical and physical database structure

Definitions and space allocations of objects

Integrity constraints

Users

Roles

Privileges

Auditing

D t Di ti Vi C t i


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Data Dictionary View Categories

The data dictionary consists of three main sets ofstatic views distinguished from each other by theirscope:

DBA:What is in all the schemas

ALL:What the user can accessUSER:What is in the user's schema

DBA_xxx

USER_xxx

ALL_xxx

Objects owned by the current user

Objects accessible by the current user

All of the objects in the database


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Oracle Instance

Oracle Database

Database Files


Data Dictionary

Schema And Users



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Schema Objects

Tables

Triggers

Constraints

Indexes

Views

Sequences

Stored program units

Synonyms

User-defined data types

Database links

Database Schema

A schema is a namedcollection of objects

A user is created, and acorresponding schemacan be created

User can be associatedonly with one schema

Username and schemaare often used

interchangeably Users are not

necessarily associatedwith a schema


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An Oracle server consists of an Oracle instance and

an Oracle database

An Oracle instance consists of several required and

some more optional processes (threads)

An Oracle database is built using different file types



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02_DB Architecture Overview.ppt

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