2988489 Oracle Architecture

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Oracle Instance Architecture

By:-Ankit Shinde

IndiaMail:- [email protected]


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OracleArchitecture

Overview


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Oracle ArchitectureThe Oracle Server

Oracle server

Oracle server


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Oracle ArchitectureInstance Architecture

Shared pool

Library

Cache

Data

Dict io ary

Cache

Redo

Log

Buffer

Databa e

Buffer

Cache

SGA

I ta ce

DBWR LGWR SMON PMON ARC

RECO CKPT LCK SNP D

S


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Oracle ArchitectureInstance

An Oracle instance:

Is a means to access an Oracle database Always opens one and only one database

Consists of:

Internal memory structures

Processes


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Oracle ArchitectureInteraction with the Database ( Dedicated Server)

SGA

Reque

t Re

po

e

Shared SQL

Po ol D ataba

e Buffer CacheRedo log Buffer

Databa

e File Redo Log F i le

Dedicated

Se r

er

U

er

Proce

D BW R LG W R AR C

P MONS MONCKP T


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SG

R

q

t R

po

S

r d SQL

Pool D

t

b

B

ff

r C

R do log B ff r

D t b

Fi l R

do Log Fil

U

r

Pr o

DBW R LG WR

RC

PM

NSM

N

D

di

t

d

S

r

rD di t d

S

r

rS

r d

S

r

r

U

r

Pr o

U

r

Pr o

U

r

Pr o

U

rPr o

Di

p

t

r

CKPT

r l r it t r Interaction with the Database ( Shared Server)


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Oracle ArchitectureInternal Memory Structures SGA

System or shared Global Area (SGA)

Database buffer cache Redo log buffer

Shared pool

Request & response queues (shared server)


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Oracle ArchitectureDatabase buffer cache

Used to hold data blocks read from datafiles by server

processes Contains dirty or modified blocks and clean or

unused or unchanged bocks

Dirty and clean blocks are managed in lists called the

dirty list and the LRU

Free space is created by DBWR writing out dirty

blocks or aging out blocks from the LRU

Size is managed by the parameter

DB_BLOCK_BUFFERS


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Oracle ArchitectureLeast Recently Used (LRU)

LRU and the database buffer cache

Every time a data block is read from disk it is placedin the database buffer cache at the head of the LRU

list

If a block is already in the cache and it is read again

it is moved to the head of the list

Data not used frequently is aged out of the cache

while frequently used data remains


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Oracle ArchitectureRedo Log Buffer

A circular buffer that contains redo entries

Redo entries reflect changes made to the database Redo entries take up contiguous, sequential

space in the buffer

Data stored in the redo log buffer is periodically

written to the online redo log files Size is managed by the parameter

LOG_BUFFER Default is 4 times the maximum data block size for

the operating system


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Oracle ArchitectureShared Pool

Consists of multiple smaller memory areas Library cache

Shared SQL area

Contains parsed SQL and execution plans for statements alreadyrun against the database

Procedure and package storage

Dictionary cache

Names of all tables andv

iews in the database Names and datatypes of columns in the database tables

Privileges of all users

Managed via an LRU algorithm

Size determined by the parameter

SHARE

D_POO

L_SIZE


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Oracle ArchitectureLeast Recently Used (LRU)

LRU and the shared pool

Every time a SQL statement is parsed it is placed inthe shared pool for reuse

If a SQL statement is already in the shared pool itwill not re-parse but it is placed at the head of theLRU

SQL statements not used frequently are aged outof the shared pool while frequently used statementsremain

A SQL statement may be artificially retained at thehead of the LRU by pinning the statement


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Oracle ArchitectureInternal Memory Structures PGA

Program or process Global Area (PGA)

Used for a single process Not shareable with other processes

Writable only by the server process

Allocated when a process is created anddeallocated when a process is terminated

Contains: Sort area Used for any sorts required by SQL processing

Session information Includes user privileges

Cursor state Indicates stage of SQL processing

Stack space Contains session variables


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Oracle ArchitectureBackground Processes - DBWR

Writes contents of database buffers to datafiles

Primary job is to keep the database bufferclean

Writes least recently used (LRU) dirty buffersto disk first

Writes to datafiles in optimal batch writes Only process that writes directly to datafiles

Mandatory process


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Oracle ArchitectureBackground Processes - DBWR

DBWR writes to disk when:

A server process cannot find a clean reusable buffer A timeout occurs (3 sec)

A checkpoint occurs

DBWR cannot write out dirty buffers before they

have been written to the online redo log files


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Oracle ArchitectureCommit Command

The SQL command O I allows users tosave transactions that have been made against

a database. This functionality is available for

any A , I , r

transaction; it is not available for changes todatabase objects (such as A A

commands)


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Oracle ArchitectureBackground Processes - LGWR

Writes contents of redo log buffers to online

redo log files Primary job is to keep the redo log buffer

clean

Writes out redo log buffer blocks sequentially

to the redo log files May write multiple redo entries per write during

high utilization periods

Mandatory process


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Oracle ArchitectureBackground Processes - LGWR

LGWR writes to disk when:

A transaction is COMMITED A timeout occurs (3 sec)

The redo log buffer is 1/3 full

There is more than 1 megabyte of redo entries

Before DBWR writes out dirty blocks to datafiles


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Oracle ArchitectureBackground Processes - SMON

Performs automatic instance recovery

Reclaims space used by temporary segmentsno longer in use

Merges contiguous areas of free space in the

datafiles (if PCTINCREASE > 0)

SMON wakes up regularly to check whether it

is needed or it may be called directly

Mandatory process


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Oracle ArchitectureBackground Processes - SMON

SMON recovers transactions marked as DEAD

within the instance during instance recovery All non committed work will be rolled back by SMON

in the event of server failure

SMON makes multiple passes through DEAD

transactions and only applies a specified number ofundo records per pass, this prevents short

transactions having to wait for long transactions to

recover

SMON primarily cleans up server-side failures


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Oracle ArchitectureBackground Processes - PMON

Performs automatic process recovery

Cleans up abnormally terminated connections Rolls back non committed transactions

Releases resources held by abnormally terminatedtransactions

Restarts failed shared server and dispatcherprocesses

PMON wakes up regularly to check whether itis needed or it may be called directly

Mandatory process


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Oracle ArchitectureBackground Processes - PMON

Detects both user and server aborted database

processes Automatically resolves aborted processes

PMON rolls back the current transaction of the

aborted process

Releases resources used by the process If the process is a background process the instance

most likely cannot continue and will be shut down

PMON primarily cleans up client-side failures


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Oracle ArchitectureBackground Processes - CKPT

Forces all modified data in the SGA to be written todatafile Occurs whether or not the data has been committed

CKPT does not actually write out buffer data only DBWR canwrite to the datafiles

Updates the datafile headers This ensures all datafiles are synchronized

Helps reduce the amount of time needed to performinstance recovery

Frequency can be adjusted with parameters


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Oracle ArchitectureBackground Processes - ARCH

Automatically copies online redo log files to

designated storage once they have become full


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Oracle ArchitectureServer Processes

Services a single user process in the dedicated

server configuration or many user processes inthe shared server configuration

Use an exclusive PGA

Include the Oracle Program Interface (OPI)

Process calls generated by the client Return results to the client in the dedicated

server configuration or to the dispatcher in theshared server configuration


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Oracle ArchitectureUser Processes

Run on the client machine

Are spawned when a tool or an application isinvoked

SQL*Plus, Server Manager, Oracle Enterprise

Manager, Developer/2000

Custom applications

Include the User Program Interface (UPI)

Generate calls to the Oracle server


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Oracle ArchitectureTransaction Example - Update

SGA

Databa

e

Buffer

Cache

Shared Pool

Redo

Lo g

Buffer

Databa

e File Redo Lo g Fi le

Dedicated

Se r

er

U

er

Proce

DB W R L G W R

P MONSMONCKP T

Rol lback

S egme t

1

2

UPDAT table

S T u er = SHIP RT

WH R id = 12345


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SGA

Databa

e

Buffer

Cache

Shared Pool

Redo

Lo g

Buffer

Databa


Dedicated

Se r

er

U

er

Proce

DB W R L G W R

P MONSMONCKP T

Rol lback

S egme t


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SGA

Databa

e

Buffer

Cache

Shared Pool

Redo

Lo g

Buffer

Databa


Dedicated

Se r!

er

U

er

Proce

DB W R L G W R

P MONSMONCKP T

Rol lback

S egme " t

#


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SGA

Databa$

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Buffer

Cache

Shared Pool

Redo

Lo g

Buffer

Databa$

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$

Dedicated

Se r%

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Proce$ $

DB W R L G W R

P MONSMONCKP T

Rol lback

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'


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SGA

Databa(

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Buffer

Cache

Shared Pool

Redo

Log

Buffer

Databa(

e File(

Redo Log File(

Dedicated

Ser)

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U(

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Proce( (

DBWR LGWR

PMONSMONCKPT

Rollback

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SGA

Databa1

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Buffer

Cache

Shared Pool

Redo

Log

Buffer

Databa1

e File1

Redo Log File1

Dedicated

Ser2

er

U1

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Proce1 1

DBWR LGWR

PMONSMONCKPT

Rollback

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SGA

Databa4

e

Buffer

Cache

Shared Pool

Redo

Log

Buffer

Databa4

e File4

Redo Log File4

Dedicated

Ser5

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U4

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Proce4 4

DBWR LGWR

PMONSMONCKPT

Rollback

Segme 6 t

8ROW UPDAT D


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SGA

Databa7

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Buffer

Cache

Shared Pool

Redo

Log

Buffer

Databa7

e File7

Redo Log File7

Dedicated

Ser8

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U7

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Proce7 7

DBWR LGWR

PMONSMONCKPT

Rollback

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109COMMIT


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SGA

Databa@

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Buffer

Cache

Shared Pool

Redo

Log

Buffer

Databa@

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Redo Log File@

Dedicated

SerA

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DBWR LGWR

PMONSMONCKPT

Rollback

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11COMMIT

SUCC SSFUL


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SGA

DatabaC

e

Buffer

Cache

Shared Pool

Redo

Log

Buffer

DatabaC

e FileC

Redo Log FileC

DBWR LGWR

PMONSMONCKPT

Rollback

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2988489 Oracle Architecture