basic oracle

8/11/2019 basic oracle

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ORACLE

INSTANCE

ARCHITECTURE


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INTRODUCTION TO THE ORACLE DATABASE

INSTANCE

A database instance is a set of memory

structures that manage database files a a ase s a se o p ys ca es on s

The instance manages its associated data and

Every running Oracle database is associated

Instance can exist without Database


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DATABASE INSTANCE STRUCTURE

What happens When an instance is started, Oracle Database allocates a memory area called the

system global area (SGA)

.

serves various purposes, including the following:


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DATABASE INSTANCE STRUCTURE

What does SGA does

Maintaining internal data structures that are accessed

Caching data blocks read from disk

Bufferin redo data before writin it to the online redo

log files Storing SQL execution plans


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DATABASE INSTANCE CONFIGURATIONS

You can run Oracle Database in either of the

following mutually exclusive configurations: -

A one-to-one relationship exists between the database and an

instance

Oracle Real Application Clusters (Oracle RAC)

one-to-many relationship exists between the database andinstances


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Whether in a single-instance or Oracle RAC

configuration, a database instance is associated.

(associate the instance with) one database, but not

mount two databases simultaneousl with the same

instance

Multiple instances can run concurrently on the

same computer/ Server, each accessing its own

database


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Duration of an Instance

An instance begins when it is created with the

Durin this eriod an instance can associate itself with

one and only one database


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INSTANCE AND DATABASE STARTUP


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DATABASE AND INSTANCE SHUTDOWN


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SHUTDOWN MODES


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CHECKPOINTS

A checkpoint is a crucial mechanism in

consistent database shutdowns, instance,

Reduce the time required for recovery in case of an

instance or media failure

Ensure that dirty buffers in the buffer cache are written

to disk regularly Ensure that all committed data is written to disk during a

consistent shutdown


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INSTANCE RECOVERY

Instance recovery is the process of applying

records in the online redo log to data files to

checkpoint

Instance recovery occurs automatically when an

administrator attem ts to o en a database that was

previously shut down inconsistently.

Instance recovery ensures that the database is in a

consistent state after an instance failure.


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WHEN ORACLE DATABASE PERFORMS

INSTANCE RECOVERY

e er ns ance recovery s requ re epen s onthe state of the redo threads.

A redo thread is marked open in the control filewhen a database instance opens in read/write

mode, and is marked closed when the instance isshut down consistently.

The database opens for the first time after the

-of an Oracle RAC database

Some but not all instances of an Oracle RACdatabase fail


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PARAMETER FILES

To start a database instance, Oracle Database

must read either a server parameter file, which is,

file, which is a legacy implementation.

These files contain a list of configuration

arameters


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PARAMETER FILES

Server Parameter Files

A server parameter file is a repository for initialization.

Characteristics of Server Parameter file.

The server parameter file is written to and read only byOracle Database

The server parameter file is binary file


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PARAMETER FILES

Text Initialization Parameter Files

A text initialization parameter file is a text file that.

.

Reside on the same host

A text initialization parameter file is text-based, not

binary

Oracle Database can read but not write to the text


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ORACLE DATABASE MEMORY STRUCTURES

When an instance is started, Oracle Database

allocates a memory area and starts background.

The memory area stores information such as the

Program code

Information about each connected session

Information needed during program execution

Information such as lock data that is shared andcommunicated among processes

Cached data, such as data blocks and redo records,


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BASIC MEMORY STRUCTURES

ys em g o a area

The SGA is a group of shared memory structures,known as SGA com onents that contain data andcontrol information for one Oracle Databaseinstance

A PGA is a nonshared memory region that contains dataand control information exclusively for use by an Oracleprocess

User Global Area (UGA)

.

Software code areas

Software code areas are ortions of memor used tostore code that is being run or can be run.


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DATABASE MEMORY MANAGEMENT

Memory management involves maintaining optimal

sizes for the Oracle instance memory structures as

Automatic memory management

Partially automated

Manual memory management

Instead of setting the total memory size individually set SGA

and PGA memmory.


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USER GLOBAL AREA

The UGA is session memory

Memory allocated for session variables ogon n orma on

P/L SQL Package State.


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PROGRAM GLOBAL AREA

The PGA is memory specific to an operating

process or thread that is not shared by other

- ,

SGA.


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CONTENTS OF THE PGA


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CONTENTS OF THE PGA

Private SQL Area

The run-time area

The ersistent area

This area contains variable valuesA variable value is supplied to a SQL statement at run time

SQL Work Areas A work area is a private allocation of PGA memory

used for memory-intensive operations.


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SYSTEM GLOBAL AREA

The SGA is a read/write memory area that, along

with the Oracle background processes, make up a

can read information in the instance SGA

Each database instance has its own SGA.


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SGA COMPONENTS

The most important SGA components are the

following

Redo Log Buffer

Large Pool

Java Pool

Fixed SGA


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DATABASE BUFFER CACHE

The database buffer cache, also called the buffer

cache, is the memory area that stores copies of

.

Why Buffer Cache

Keep frequently accessed blocks in the buffer cache

and write infrequently accessed blocks to disk


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BUFFER STATES

The database uses internal algorithms to manage

buffers in the cache

u er can e n any o e o ow ng mu ua y

exclusive states:

The buffer is available for use because it has never been usedor is currently unused

Clean

This buffer was used earlier and now contains a read-

consistent version of a block as of a point in time. Dirty

The buffer contain modified data that has not yet been written


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REDO LOG BUFFER

The redo log buffer is a circular buffer in the SGA

that stores redo entries describing changes made

.

reconstruct, or redo, changes made to the databaseb DML or DDL o erations.

to reconstruct lost changes.


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SHARED POOL

The shared pool caches various types of

program data

System Parameters

.


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LARGE POOL

The large pool is an optional memory area

intended for memory allocations that are larger

with multiple databases

Message buffers used in the parallel execution of

statements

Buffers for Recovery Manager (RMAN)


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JAVA POOL

The Java pool is an area of memory that stores all

session-specific Java code and data within the Java

.


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FIXED SGA

The fixed SGA is an internal housekeeping area

General information about the state of the database and

the instance, which the background processes need to

access

Information communicated between processes, such as

information about locks


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INTRODUCTION TO PROCESSES

A process is a mechanism in an operating

system that can run a series of steps

All connected Oracle Database users must run the

Application or Oracle Database utility

A rocess normall runs in its own rivate memorarea


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TYPES OF PROCESSES

Client processes

run the application

rac e oo co e

Oracle processes

Background processes start with the database instance

perform maintenance tasks (instance recovery, cleaning up

processes , writing redo buffers to disk .)

perform additional tasks for a background or server process


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CLIENT PROCESSES

When a user runs an application such as a Pro*C

program or SQL*Plus, the operating system creates

to run the user application.

The client application has Oracle Database librarieslinked into it that rovide the APIs re uired to

communicate with the database.


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CONNECTIONS AND SESSIONS

Connection

A connection is a physical communication

pa way e ween a c en process an a

database instance

A communication pathway is established using

mechanisms or network software


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CONNECTIONS AND SESSIONS

Session

A session is a logical entity in the database

ns ance memory a represen s e s a e o a

current user login to a database

, ,

sessions established on it

session does not affect transactions in other

sessions


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SERVER PROCESSES

Oracle Database creates server processes to

an e e reques s o c en processes connec e

to the instance

A client process always communicates with a.


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DEDICATED SERVER PROCESSES

In dedicated server connections, the client

connection is associated with one and only one

Each client process communicates directly with its

This server process is dedicated to its clientrocess for the duration of the session.


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SHARED SERVER PROCESSES

In shared server connections, client applications

connect over a network to a dispatcher process, not

The dispatcher process receives requests from

queue in the large pool The first available shared server rocess takes the

request from the queue and processes it.

shared server place the result into the dispatcherresponse queue


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BACKGROUND PROCESSES

Mandatory Background Processes

Optional Background Processes

Slave Processes


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MANDATORY BACKGROUND PROCESSES

The mandatory background processes are present

in all typical database configurations

System Monitor Process (SMON)

Log Writer Process (LGWR) Checkpoint Process (CKPT)

Manageability Monitor Processes (MMON and MMNL)

Recoverer Process (RECO)

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basic oracle