19857623 Basic Oracle Architecture

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Basic Oracle ArchitectureBasic Oracle Architecture

Presented to HIOUGPresented to HIOUG21-Jun-200521-Jun-2005

By Byron BushBy Byron Bush


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Workshop ObjectivesWorkshop Objectives

Identify high-level architecturalcomponents of an Oracle Database

Describe the function of each of these

components Identify Oracle Database internal data

structures

Define the mechanisms used whenprocessing Insert/Update/Deletestatements


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Most people call it a DatabaseMost people call it a Database

Technically an Oracle Database is broken

into two high-level components

INSTANCE Non-persistent, memory-

based processes and structures

DATABASE Persistent, disk-based data

and control files


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So Why Differentiate?So Why Differentiate?

Most Oracle installations consist of only a

single Instance and single Database

Instance

Database


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Oracle RAC is DifferentOracle RAC is Different

Oracle Real Application Clusters allow

multiple Instances to interact with a

single Database to provide high

availability

Instance 1

Database

Instance 3Instance 2


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Instance a Little CloserInstance a Little Closer

An Oracle Instance

Is a means to access an Oracle Database

Always opens one and only one Database

Consists of memory and background process

structures


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Picture of an InstancePicture of an Instance

Instance

Library

Cache

Data

Dictionary

Cache

Shared PoolSGA

Database Buffer

Cache

Redo Log

Buffer

Java Pool Large Pool

PMON SMON DBWR LGWR CKPT Others

MemoryStructures

Back-Ground

Processes


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Database a Little CloserDatabase a Little Closer

An Oracle Database

Is a collection of data that is treated as a unit

Consists of three file types


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Picture of a DatabasePicture of a Database

Archived

Log Files

Parameter

File

Password

File

Oracle Database

Data Files Control Files Redo Log Files


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Instance

Library

Cache

Data

Dictionary

Cache

Shared PoolSGA

Database Buffer

Cache

Redo Log

Buffer



MemoryStructures

Back-Ground

Processes


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Memory StructureMemory Structure

Oracles memory structure consists of two

memory areas known as:

2. System Global Area (SGA): Allocated at

instance start up, and is a fundamental

component of an Oracle Instance

3. Program Global Area (PGA): Allocated

when the server process is started


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System Global AreaSystem Global Area

The SGA consists of several memory structures:

Shared Pool

Database Buffer Cache

Redo Log Buffer Other structures

There are two additional memory structures that

can be configured within the SGA:

Large Pool

Java Pool


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System Global AreaSystem Global Area

The size of the SGA is determined by the

parameters that set the sizes of the

various pools; these parameters are

dynamic

The SGA_MAX_SIZE parameter sets the

maximum size of the SGA (so you can

limit it) and is not a dynamic parameter

Thanks Ned!


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Instance

Library

Cache

Data

Dictionary

Cache

Shared PoolSGA

Database Buffer

Cache

Redo Log

Buffer



MemoryStructures

Back-Ground

Processes


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Shared PoolShared Pool

Used to store: Most recently executed SQL statements

Most recently used data definitions

It consists of two key performance-relatedmemory structures: Library Cache

Data Dictionary Cache Sized by the parameter

SHARED_POOL_SIZE


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Library CacheLibrary Cache

Stores information about the most recently usedSQL and PL/SQL statements

Enables the sharing of commonly used

statements Is managed by a least recently used (LRU)algorithm

Consists of two structures

Shared SQL area Shared PL/SQL area

Size is determined by the Shared Pool sizing


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Instance

Library

Cache

Data

Dictionary

Cache

Shared PoolSGA

Database Buffer

Cache

Redo Log

Buffer



MemoryStructures

Back-Ground

Processes


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Data Dictionary CacheData Dictionary Cache

A collection of the most recently useddefinitions in the database

Includes information about database files,

tables, indexes, columns, users,privileges, and other database objects

During the parse phase, the server

process looks at the data dictionary forinformation to resolve object names andvalidate access


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Database Buffer CacheDatabase Buffer Cache

Stores copies of data blocks that have

been retrieved from the data files

Enables great performance gains when

you obtain and update data

Managed through an LRU algorithm

DB_BLOCK_SIZE determines primaryblock size


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Instance

Library

Cache

Data

Dictionary

Cache

Shared PoolSGA

Database Buffer

Cache

Redo Log

Buffer



MemoryStructures

Back-Ground

Processes


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Large PoolLarge Pool

An optional area of memory in the SGA

Relieves the burden place on the Shared Pool

Used for:

Session memory for the Shared Server

I/O server processes

Backup and restore operations for RMAN

Does not use an LRU list Sized by LARGE_POOL_SIZE

Can be dynamically resized


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Java PoolJava Pool

Services parsing requirements for Java

commands

Required if installing and using Java

Sized by JAVA_POOL_SIZE parameter


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Oracle Process StructureOracle Process Structure

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 started when a user

establishes a session Background Processes: Started when an

Oracle instance is started


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User ProcessUser Process

A program that requests interaction with the

Oracle server

Must first establish a connection

Does not interact directly with the Oracle server

Server

Process

User

ProcessConnection

Established


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Server ProcessServer Process

A program that directly interacts with the

Oracle server

Fulfills calls generated and returns results

Can be dedicated or shared server


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Instance

Library

Cache

Data

Dictionary

Cache

Shared PoolSGA

Database Buffer

Cache

Redo Log

Buffer



MemoryStructures

Back-Ground

Processes


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Background ProcessesBackground Processes

Maintains and enforces relationshipsbetween physical and memory structures Mandatory background processes:

DBWn PMON CKPTLGWR SMON

Optional background processes:ARCn LMDn QMNn

CJQ0 LMON RECODnnn LMS Snnn

LCKn Pnnn


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Database Writer (DBWn)Database Writer (DBWn)

DBWn writes when: Checkpoint occurs

Dirty buffers reach

threshold

There are no free

buffers Timeout occurs

Tablespace OFFLINE

Tablespace READ

ONLY

Table DROP or

TRUNCATE

Tablespace BEGIN

BACKUP

Oracle

DatabaseData Files Control Files Redo Log Files

Instance

Shared Pool

Library

Cache

Data

Dictionary

Cache

SGA

Database Buffer

Cache

Redo Log

Buffer



Shared Pool


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Log Writer (LGWR)Log Writer (LGWR)

LGWR writes: At commit

When one-third full

When there is 1 MB of

redo

Every three seconds Before DBWn writes

Instance

Shared Pool

Library

Cache

Data

Dictionary

Cache

SGA

Database Buffer

Cache

Redo Log

Buffer



Oracle



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System Monitor (SMON)System Monitor (SMON)

Responsibilities: Instance recovery

Rolls forward

changes in online

redo log files

Opens database for

user access Rolls back

uncommitted

transactions

Coalesces free space

Deallocates temporary

segments

Oracle


Instance

Shared Pool

Library

Cache

Data

Dictionary

Cache

SGA

Database Buffer

Cache

Redo Log

Buffer



Shared Pool


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Process Monitor (PMON)Process Monitor (PMON)

Cleans up after failedprocesses by:

Rolling back the

transaction

Releasing locks

Releasing otherresources

Restarting dead

dispactchers

Database Buffer

Cache

Oracle


Instance

Shared Pool

Library

Cache

Data

Dictionary

Cache

SGA

Redo Log

Buffer



Shared Pool


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Checkpoint (CKPT)Checkpoint (CKPT)

Responsible for: Signaling DBWn at

checkpoints

Updating datafile

headers with

checkpoint information

Updating control files

with checkpoint

information

Instance

Shared Pool

Library

Cache

Data

Dictionary

Cache

SGA

Database Buffer

Cache

Redo Log

Buffer



Oracle


Shared Pool


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Archiver (ARCn)Archiver (ARCn)

Optional background process Automatically archives online redo log files when

ARCHIVELOG mode is set Preserves the record of all changes made to the

databaseOracle

DatabaseData Files Control Files Redo Log Files Archived Logs

ARCn


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Oracle Data StorageOracle Data Storage

Oracle keeps all system and user data in

two basic storage containers:

Tablespace a logical entity known

only to Oracle

Data Files physical files that may

(typically) be seen from the operating

system


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TablespacesTablespaces

Can belong to only one database at a time

Consist of one or more data files

Are further divided into logical units ofstore


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Data FilesData Files

Can belong to only one tablespace and

one database

Are a repository for schema object data

DataFile DataFile

Database

Tablespace


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2 Types of Tablespace2 Types of Tablespace

1. Tablespaces required by Oracle for

normal operations

2. Tablespaces that contain data and

indexes that support your applications


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Required TablespacesRequired Tablespaces

System Contains the Oracle Data

Dictionary

Sysaux - New to 10g; supports historic

monitoring / tuning

Temporary Used for disk-based sorting

of data (select...fromorder by)

Undo Used for transaction consistency

during Insert / Update / Delete statements


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SQL Statements (IUDS)SQL Statements (IUDS)

Insert

Update

Delete Select

What happens when

someone connects to

the database and

issues one of thesestatements?


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Connect to Oracle What HappensConnect to Oracle What Happens

Server

Process

User

ProcessConnect User/Pwd

Are User definition and privileges in SGADictionary Cache? If not, try to fetch from the System

tablespace

If there, validate Pwd and privileges to loginAllow connection if all is right; otherwise

decline connection


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Select What Happens First?Select What Happens First?

Is this statement in the Library Cache?

If statement cached then it has been recently

been parsed and executed

If not cached then parse the statement

If cached then skip parsing stage and executestatement

Select *

From MyTabOrder by 1;


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Select Parsing the StatementSelect Parsing the Statement

Does MyTab exist?

Does user have Privs to select from

MyTab

What columns are in MyTab

What is the first column in MyTab

Select *



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Select Executing the StatementSelect Executing the Statement

Is MyTab data in the SGA Buffer Cache?

If not, fetch data into Buffer Cache

Sort data in MyTab by the first column

If can sort records in memory then do so

If cannot sort in memory then use Temporarytablespace as disk-based staging area

Return records to client process

Select *



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I/U/D What Happens First?I/U/D What Happens First?

Is this statement in the Library Cache?

If statement cached then it has been recently

been parsed and executed

If not cached then parse the statement

If cached then skip parsing stage and executestatement

Insert (a,b,c)

Into MyTab;


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I/U/D Executing the StatementI/U/D Executing the Statement

Validate values to be inserted

Execute the statement Keep DB version of the record in Undo

tablespace until Commit or Rollback

Record changes in SGA Redo Log Buffer Change records in SGA Buffer Cache

DBWn writes changed records to data file(s)as part of buffer cache management

Insert (a,b,c)

Into MyTab;


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I/U/D Executing the StatementI/U/D Executing the Statement

If Commit then

LGWn writes Redo Log Buffer entries to

Redo Logs

Undo entries are invalidated

If Rollback then Migrate DB version of record in Undo back to

tablespace/data file

Insert (a,b,c)

Into MyTab;

Commit;

or

Rollback;


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Archivelog ModeArchivelog Mode

Oracle

DatabaseData Files Control Files Redo Log Files Archived Logs

ARCn

If Instance in Archivelog mode Redo LogFiles are Archived to Archive Logs;

which may be used to recover your

database in the case of disaster


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SummarySummary What we called a Database is really an

Instance and a Database. An Oracle Instance is not persistent. It consists

of the System Global Area (SGA) and acollection of processes.

An Oracle Database is persistent. It consists ofa collection of Required and Usertablespaces (with corresponding data files)along with other supporting files.

Nearly every component of the Instance andDatabase are mobilized to execute SQLstatements.

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19857623 Basic Oracle Architecture