02 oracle architecture

8/12/2019 02 Oracle Architecture

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Oracle

Architecture

Overview


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Oracle Architecture

The OracleServer

Oracle server

Oracle server


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Oracle Architecture

Instance Architecture

Shared pool

Library

Cache

Data

Dictionary

Cache

Redo

Lo g

Buffer

Database

Buffer

Cache

SGA

Instance

DBWR LGWR SO! "O! ARCn

R#CO C$"% LC$n S!"n Dnnn

Snnn


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Oracle Architecture

Instance

An Oracle instance:

Is a means to access an Oracle data!ase Always o"ens one and only one data!ase

#onsists o$: Internal memory structures

%rocesses


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Oracle Architecture

Interaction with the &ata!ase ' &edicated Server (

SGA

Re&uest Response

Shared S'L

"ool Database Buffer CacheRedo log Buffer

Database (iles Redo Log (iles

Dedicated

Server

)ser

"rocess

DBWR LGWR ARCn

"O!SO!C$"%


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SG A

Re&uest Response

Shared S'L

"ool Database Buffer CacheRedo log Buffer

Database (iles Redo Log (iles

)ser

"rocess

DBWR LGWR ARCn

"O!SO!

Dedicated

Server

Dedicated

Server

Shared

Servers

)ser

"rocess

)ser

"rocess

)ser

"rocess

)ser"rocess

Dispatcher

C$"%

Oracle Architecture

Interaction with the &ata!ase ' Shared Server (


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Oracle Architecture

Internal Memory Structures S)A

System or *shared+ )lo!al Area 'S)A(

&ata!ase !u$$er cache ,edo log !u$$er

Shared "ool

,euest res"onse ueues 'shared server(


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Oracle Architecture

&ata!ase !u$$er cache

/sed to hold data !locks read $rom data$iles !y server

"rocesses

#ontains *dirty+ or modi$ied !locks and *clean+ or

unused or unchanged !ocks

*&irty+ and *clean+ !locks are managed in lists called the

dirty list and the 0,/

1ree s"ace is created !y &B2, writing out *dirty+

!locks or aging out !locks $rom the 0,/

Si3e is managed !y the "arameter

&B4B0O#54B/116,S


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Oracle Architecture

0east ,ecently /sed '0,/(

0,/ and the data!ase !u$$er cache

6very time a data !lock is read $rom disk it is "lacedin the data!ase !u$$er cache at the head o$ the 0,/

list

I$ a !lock is already in the cache and it is read again

it is moved to the head o$ the list

&ata not used $reuently is *aged+ out o$ the cache

while $reuently used data remains


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Oracle Architecture

,edo 0og Bu$$er

A circular !u$$er that contains redo entries ,edo entries re$lect changes made to the data!ase

,edo entries take u" contiguous7 seuentials"ace in the !u$$er

&ata stored in the redo log !u$$er is "eriodically

written to the online redo log $iles Si3e is managed !y the "arameter

0O)4B/116, &e$ault is 8 times the ma9imum data !lock si3e $or

the o"erating system


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Oracle Architecture

Shared %ool

#onsists o$ multi"le smaller memory areas 0i!rary cache

Shared S0 area #ontains "arsed S0 and e9ecution "lans $or statements already run

against the data!ase

%rocedure and "ackage storage

&ictionary cache ;ames o$ all ta!les and views in the data!ase ;ames and dataty"es o$ columns in the data!ase ta!les %rivileges o$ all users

Managed via an 0,/ algorithm Si3e determined !y the "arameter

S


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Oracle Architecture

0east ,ecently /sed '0,/(

0,/ and the shared "ool 6very time a S0 statement is "arsed it is "laced in

the shared "ool $or reuse

I$ a S0 statement is already in the shared "ool itwill not re-"arse !ut it is "laced at the head o$ the0,/

S0 statements not used $reuently are *aged+ outo$ the shared "ool while $reuently used statementsremain

A S0 statement may !e arti$icially retained at thehead o$ the 0,/ !y *"inning+ the statement


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Oracle Architecture

Internal Memory Structures %)A

%rogram or *"rocess+ )lo!al Area '%)A( /sed $or a single "rocess

;ot sharea!le with other "rocesses

2rita!le only !y the server "rocess

Allocated when a "rocess is created anddeallocated when a "rocess is terminated

#ontains:Sort area /sed $or any sorts reuired !y S0 "rocessingSession in$ormation Includes user "rivileges#ursor state Indicates stage o$ S0 "rocessing

Stack s"ace #ontains session varia!les


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Oracle Architecture

Background %rocesses - &B2,

2rites contents o$ data!ase !u$$ers to data$iles

%rimary >o! is to kee" the data!ase !u$$er*clean+2rites least recently used '0,/( *dirty+ !u$$ers

to disk $irst

2rites to data$iles in o"timal !atch writesOnly "rocess that writes directly to data$ilesMandatory "rocess


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Oracle Architecture

Background %rocesses - &B2,

&B2, writes to disk when:

A server "rocess cannot $ind a clean reusa!le !u$$er A timeout occurs '? sec(

A check"oint occurs

&B2, cannot write out *dirty+ !u$$ers !e$ore they

have !een written to the online redo log $iles


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Oracle Architecture

Background %rocesses - 0)2,

2rites contents o$ redo log !u$$ers to onlineredo log $iles

%rimary >o! is to kee" the redo log !u$$er*clean+

2rites out redo log !u$$er !locks seuentially

to the redo log $ilesMay write multi"le redo entries "er write during

high utili3ation "eriodsMandatory "rocess


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Oracle Architecture

Background %rocesses - 0)2,

0)2, writes to disk when:

A transaction is #OMMIT6& A timeout occurs '? sec(

The redo log !u$$er is ? $ull

There is more than mega!yte o$ redo entries

Be$ore &B2, writes out *dirty+ !locks to data$iles


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Oracle Architecture

Background %rocesses - SMO;

%er$orms automatic instance recovery

,eclaims s"ace used !y tem"orary segmentsno longer in use

Merges contiguous areas o$ $ree s"ace in the

data$iles 'i$ %#TI;#,6AS6 C D(

SMO; *wakes u"+ regularly to check whether it

is needed or it may !e called directly

Mandatory "rocess


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Oracle Architecture

Background %rocesses - SMO;

SMO; recovers transactions marked as &6A&

within the instance during instance recovery All non committed work will !e rolled !ack !y SMO;in the event o$ server $ailure

SMO; makes multi"le "asses through &6A&

transactions and only a""lies a s"eci$ied num!er o$undo records "er "ass7 this "revents short

transactions having to wait $or long transactions to

recover

SMO; "rimarily cleans u" server-side $ailures


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Oracle Architecture

Background %rocesses - %MO;

&etects !oth user and server a!orted data!ase

"rocessesAutomatically resolves a!orted "rocesses

%MO; rolls !ack the current transaction o$ the

a!orted "rocess

,eleases resources used !y the "rocess I$ the "rocess is a !ackground "rocess the instance

most likely cannot continue and will !e shut down

%MO; "rimarily cleans u" client-side $ailures


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Oracle Architecture

Background %rocesses - #5%T

1orces all modi$ied data in the S)A to !e written todata$ile

Occurs whether or not the data has !een committed #5%T does not actually write out !u$$er data only &B2, can

write to the data$iles

/"dates the data$ile headers This ensures all data$iles are synchroni3ed

usted with "arameters


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Oracle Architecture

Background %rocesses - A,#

02 oracle architecture

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