less01_exploring oracle database architecture

8/6/2019 Less01_Exploring Oracle Database Architecture

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Copyright 2008, Oracle. All rights reserved.

Exploring the Oracle Database Architecture


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Copyright 2008, Oracle. All rights reserved.1 - 2

Objectives

After completing this lesson, you should be able to:

List the major architectural components of Oracle

Database

Explain the memory structures

Describe the background processes

Correlate the logical and physical storage structures


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Oracle Database

The Oracle relational database management system

(RDBMS) provides an open, comprehensive, integrated

approach to information management


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Connecting to a Server

Client Middle tier Server

Multitier architecture shown


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Database

Data filesOnline redo

log files

Controlfiles

Oracle Database Architecture: Overview

Database

buffer

cache

Shared pool

Data dictionarycache

Library

cache

PMONSMON Others

Server

process

PGA

Archived

log filesUser

process

Instance

RECO

ARCn

SGA

DBWn

Redo log

buffer

LGWRCKPT


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Connecting to the Database

Connection: Communication between a user process

and an instance

Session: Specific connection of a user to an instance

through a user process

SQL> Select Session

Connection

User

User

process

Server

process

Session


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Interacting with an Oracle Database

User

Database

buffer

cache

Shared pool

Data dictionary

cache

Library

cache

PMONSMON Others

Instance

RECOARCn

SGA

DBWn

Redo log

buffer

LGWRCKPT

User

process

Server

process


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Database

Oracle Database Server Structures

PMONSMON Others

Data filesOnline redo

log filesControl

files

Instance

RECOARCnDBWn LGWRCKPT

Storage structures

User

process

Server

process

Memory structures

Processes

Database

buffer

cache

Shared pool

Data dictionary

cache

Library

cache

SGA

Redo log

buffer


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Oracle Database

Memory Structures

DB structures

Memory

- Process

- Storage

SGA

Database buffer

cache

Redo log

buffer

Java

pool

Streams

pool

Shared pool

Large pool

PGA PGA PGABackground

process

Server

process 1

Server

process 2

Shared

SQL area

Library

cache

Data dictionarycache

Other

I/O buffer

Response

queue

Request

queue

Freememory


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Database Buffer Cache

Is part of the SGA

Holds copies of data blocks that are read from data files

Is shared by all concurrent users

PMONSMON Others

Instance


Database

buffercache

Shared pool

Data dictionary

cache

Library

cache

SGA

Redo log

buffer


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Redo Log Buffer

Is a circular buffer in the SGA

Holds information about changes made to the database

Contains redo entries that have the information to redo

changes made by operations such as DML and DDL

PMONSMON Others

Instance


Database

buffercache

Shared pool

Data dictionary

cache

Library

cache

SGA

Redo log

buffer


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Shared Pool

Is a portion of the SGA

Contains:

Library cache

Shared SQL area

Data dictionary cache Control structures

PMONSMON Others

Instance


Shared

SQL area

Library

cache

Data dictionary

cache

Other

Databasebuffer

cache

Shared pool

Data dictionary

cache

Library

cache

SGA

Redo log

buffer


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Allocation and Reuse of Memory

in the Shared Pool

Server process checks the shared pool to see if a

shared SQL area already exists for an identical

statement.

Server process allocates a private SQL area on behalf of

the session.

Server

process

Shared

pool

Shared

SQL area

Library

cache

Data dictionary

cache

Other


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Large Pool

Provides large memory allocations for:

Session memory for the shared server and the Oracle

XA interface

I/O server processes

Oracle Database backup and restore operations

Large pool

I/O buffer

Response

queue

Request

queue

Free

memory

Java

poolLarge pool

Shared pool

Database

buffer

cache

Redo log

buffer

Streams

pool


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Java Pool

and Streams Pool

Java pool memory is used in server memory for all

session-specific Java code and data in the JVM.

Streams pool memory is used exclusively by Oracle

Streams to:

Store buffered queue messages Provide memory for Oracle Streams processes

Java pool Streams pool


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Process Architecture

User process Is started when a database user or a batch process

connects to Oracle Database

Database processes

Server process: Connects to the Oracle instance and is

started when a user establishes a session Background processes: Are started when an Oracle

instance is started

DB structures

- Memory

Process

- Storage

PMONSMON Others

Instance


PGA

User

process

Server

process Background processes

Databasebuffer

cache

Shared pool

Data dictionary

cache

Library

cache

SGA

Redo log

buffer


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Process Structures

Servern

processes

SGA

Oracle

background

processes

PMON SMON OthersRECO ARCnDBWn LGWRCKPT

Server ServerServerServer Server

Database

buffer

cache

Shared pool

Data dictionary

cache

Library

cache

SGA

Redo log

buffer


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Database Writer Process (DBWn)

Writes modified (dirty) buffers in the database buffer cache

to disk:

Asynchronously while performing other processing

Periodically to advance the checkpoint

Database buffer

cache

Database writer

process

Data files

DBWn


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LogWriter Process (LGWR)

Writes the redo log buffer to a redo log file on disk

Writes:

When a user process commits a transaction

When the redo log buffer is one-third full

Before a DBWn process writes modified buffers to disk

Redo log buffer LogWriter process Redo log files

LGWR


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Checkpoint Process (CKPT)

Records checkpoint information in

Control file

Each data file header

Checkpointprocess

Data files

Control fileCKPT


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System Monitor Process (SMON)

Performs recovery at instance startup

Cleans up unused temporary segments

Instance

Temporary

segment

System Monitorprocess

SMON


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Process Monitor Process (PMON)

Performs process recovery when a user process fails

Cleans up the database buffer cache

Frees resources that are used by the user process

Monitors sessions for idle session timeout

Dynamically registers database services with listeners

Process Monitor

processDatabase buffer

cache

Failed user

process

UserPMON


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Recoverer Process

Used with the distributed database configuration

Automatically connects to other databases involved in

in-doubt distributed transactions

Automatically resolves all in-doubt transactions

Removes any rows that correspond to in-doubttransactions

Recoverer process

in database A

In-doubt transaction

in database B

RECO


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Archiver Processes (ARCn)

Copy redo log files to a designated storage device after

a log switch has occurred

Can collect transaction redo data and transmit that data

to standby destinations

Archiver process Archive destinationCopies of redo log

files

ARCn


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Other Processes

MMON: Performs manageability-related background

tasks

MMNL: Performs frequent and lightweight

manageability-related tasks

MMAN: Performs automatic memory management tasks CJQ0: Runs user jobs used in batch processing

QMNC: Monitors the Streams Advanced Queuing

message queues


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Server Process and Database

Buffer Cache

Buffers:

Pinned

Clean

Free or unused Dirty

Database

writer

process

Database

buffer

cache

SGA

Data files

DBWn

Server

process


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Database Storage Architecture

Online redo log files

Password file

Parameter file Archived redo log

files

Control files Data files

Alert log and trace files

Backup files

DB structures

- Memory

- Process

Storage


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Logical and Physical Database Structures

Database

Logical Physical

Tablespace Data file

OS block

Segment

Extent

Oracle datablock

Schema


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Tablespaces and Data Files

Tablespaces consist of one or more data files.

Data files belong to only one tablespace.

USERS tablespace

Data file 1 Data file 2


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SYSTEMand SYSAUX Tablespaces

The SYSTEMand SYSAUX tablespaces are mandatory

tablespaces that are created at the time of database

creation. They must be online.

The SYSTEMtablespace is used for core functionality

(for example, data dictionary tables). The auxiliary SYSAUX tablespace is used for additional

database components (such as the Enterprise Manager

Repository).


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Segments, Extents, and Blocks

Segments exist in a tablespace.

Segments are collections of extents.

Extents are collections of data blocks.

Data blocks are mapped to disk blocks.

Segment Extents Datablocks

Diskblocks


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Database Architecture:

Summary of Structural Components

Memory structures:

System Global Area (SGA): Database buffer cache, redo

buffer, and various pools

Program Global Area (PGA)

Process structures: User process and server process

Background processes: SMON, PMON, DBWn, CKPT,

LGWR, ARCn, and so on

Storage structures:

Logical: Database, schema, tablespace, segment, extent,and Oracle block

Physical: Data files, control files, and redo log files


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Summary

In this lesson, you should have learned how to:

List the major architectural components of Oracle

Database

Explain the memory structures

Describe the background processes Correlate the logical and physical storage structures


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Practice 1: Overview

This is a paper practice with questions about:

Database architecture

Memory

Processes

File structures


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