This PowerPoint is based on slides from: Byron Bush, Scott S. Hilpert and Lee, JeongKyu

This PowerPoint is based on slides from:

Byron Bush, Scott S. Hilpert and Lee, JeongKyu

Advanced Databases (ADAB) 4-Feb-2010

By Henrik Høltzer

Most people call it a “Database”Technically an Oracle Database is broken into

two high-level components

1. INSTANCE – Non-persistent, memory-based processes and structures

2. DATABASE – Persistent, disk-based data and control files

So Why Differentiate?Most Oracle installations consist of only a

single “Instance” and single “Database”…

Instance

Database

Oracle RAC is DifferentOracle “Real Application Clusters” allow

multiple “Instances” to interact with a single “Database” to provide high availability…

Instance 1

Database

Instance 3Instance 2

Overview

Oracle ArchitectureInstanceAn Oracle instance:

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

Consists of:Internal memory structuresProcesses

Oracle ArchitectureInteraction with the Database ( Dedicated Server )

SGA

Request Response

Shared SQLPool Database Buffer Cache

Redo log Buffer

Database Files Redo Log Files

DedicatedServer

UserProcess

DBWR LGWR ARCn

PMONSMONCKPT

SGA

Request Response

Shared SQLPool Database Buffer Cache

Redo log Buffer


UserProcess

DBWR LGWR ARCn

PMONSMON

DedicatedServerDedicated

ServerSharedServers

UserProcessUser

ProcessUserProcessUser

Process

Dispatcher

CKPT

Oracle ArchitectureInteraction with the Database ( Shared Server )

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

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

Oracle ArchitectureRedo Log Buffer

A circular buffer that contains redo entriesRedo entries reflect changes made to the

databaseRedo entries take up contiguous, sequential

space in the bufferData stored in the redo log buffer is

periodically written to the online redo log filesSize is managed by the parameter

LOG_BUFFERDefault is 4 times the maximum data block size

for the operating system

Memory Structure : Shared Pool

Shared Pool

Library Cache

Shared SQL Area

PL/SQL Procedures

and Package

Control Structuresfor examples;

LocksLibraryCache handlesand so on ...

Dictionary Cache

Control Structuresfor example:

Character SetConversion MemoryNetwork Security Attributes

and so on ..

Shared Pool Contents

- Text of the SQL or PL/SQL statement

- Parsed form of the SQL or PL/SQL statement

- Execution plan for the SQL or PL/SQL statements - Data dictionary cache containing rows of data dictionary information

Library Cache - shared SQL area - private SQL area - PL/SQL procedures and package - control structures : lock and library cache handles Dictionary Cache - names of all tables and views in the database - names and datatypes of columns in database tables - privileges of all Oracle users SHARED_POOL_SIZE

ReusableRuntimeMemory

Oracle ArchitectureInternal Memory Structures PGA

Program or ‘process’ Global Area (PGA)Used for a single processNot shareable with other processesWritable only by the server processAllocated when a process is created and

deallocated when a process is terminatedContains:

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

Oracle ArchitectureBackground Processes - DBWRWrites contents of database buffers to

datafilesPrimary job is to keep the database buffer

‘clean’Writes least recently used (LRU) ‘dirty’

buffers to disk firstWrites to datafiles in optimal batch writesOnly process that writes directly to datafilesMandatory process

Oracle ArchitectureBackground Processes - DBWRDBWR writes to disk when:

A server process cannot find a clean reusable buffer

A timeout occurs (3 sec)A checkpoint occursDBWR cannot write out ‘dirty’ buffers before

they have been written to the online redo log files

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

Oracle ArchitectureBackground Processes - LGWR

LGWR writes to disk when:A transaction is COMMITEDA timeout occurs (3 sec)The redo log buffer is 1/3 fullThere is more than 1 megabyte of redo entriesBefore DBWR writes out ‘dirty’ blocks to

datafiles

Oracle ArchitectureBackground Processes - SMON

Performs automatic instance recoveryReclaims space used by temporary

segments no longer in useMerges 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

Oracle ArchitectureBackground Processes - SMON

SMON recovers transactions marked as DEAD within the instance during instance recoveryAll non committed work will be rolled back by

SMON in the event of server failureSMON makes multiple passes through DEAD

transactions and only applies a specified number of undo records per pass, this prevents short transactions having to wait for long transactions to recover

SMON primarily cleans up server-side failures

Oracle ArchitectureBackground Processes - PMON

Performs automatic process recoveryCleans up abnormally terminated connectionsRolls back non committed transactionsReleases resources held by abnormally

terminated transactionsRestarts failed shared server and dispatcher

processesPMON ‘wakes up’ regularly to check

whether it is needed or it may be called directly

Mandatory process

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 processReleases resources used by the processIf the process is a background process the

instance most likely cannot continue and will be shut down

PMON primarily cleans up client-side failures

Oracle ArchitectureBackground Processes - CKPT

Forces all modified data in the SGA to be written to datafileOccurs whether or not the data has been committedCKPT does not actually write out buffer data only DBWR

can write to the datafilesUpdates the datafile headers

This ensures all datafiles are synchronizedHelps reduce the amount of time needed to

perform instance recoveryFrequency can be adjusted with parameters

Oracle ArchitectureBackground Processes - ARCH

Automatically copies online redo log files to designated storage once they have become full

Oracle ArchitectureServer Processes

Services a single user process in the dedicated server configuration or many user processes in the shared server configuration

Use an exclusive PGAInclude the Oracle Program Interface (OPI)Process calls generated by the clientReturn results to the client in the dedicated

server configuration or to the dispatcher in the shared server configuration

Oracle ArchitectureUser ProcessesRun on the client machineAre spawned when a tool or an application is

invokedSQL*Plus, Server Manager, Oracle Enterprise

Manager, Developer/2000Custom applications

Include the User Program Interface (UPI)Generate calls to the Oracle server

Oracle ArchitectureTransaction Example - Update

SGA

DatabaseBufferCache

Shared Pool

RedoLogBuffer


DedicatedServer

UserProcess

DBWR LGWR

PMONSMONCKPT

RollbackSegment

1

2

UPDATE tableSET user = ‘SHIPERT’WHERE id = 12345


SGA

DatabaseBufferCache

Shared Pool

RedoLogBuffer


DedicatedServer

UserProcess

DBWR LGWR

PMONSMONCKPT

RollbackSegment

3


SGA

DatabaseBufferCache

Shared Pool

RedoLogBuffer


DedicatedServer

UserProcess

DBWR LGWR

PMONSMONCKPT

RollbackSegment

4


SGA

DatabaseBufferCache

Shared Pool

RedoLogBuffer


DedicatedServer

UserProcess

DBWR LGWR

PMONSMONCKPT

RollbackSegment

5


SGA

DatabaseBufferCache

Shared Pool

RedoLogBuffer


DedicatedServer

UserProcess

DBWR LGWR

PMONSMONCKPT

RollbackSegment

6


SGA

DatabaseBufferCache

Shared Pool

RedoLogBuffer


DedicatedServer

UserProcess

DBWR LGWR

PMONSMONCKPT

RollbackSegment

7


SGA

DatabaseBufferCache

Shared Pool

RedoLogBuffer


DedicatedServer

UserProcess

DBWR LGWR

PMONSMONCKPT

RollbackSegment

81 ROW UPDATED


SGA

DatabaseBufferCache

Shared Pool

RedoLogBuffer


DedicatedServer

UserProcess

DBWR LGWR

PMONSMONCKPT

RollbackSegment

109COMMIT


SGA

DatabaseBufferCache

Shared Pool

RedoLogBuffer


DedicatedServer

UserProcess

DBWR LGWR

PMONSMONCKPT

RollbackSegment

11COMMITSUCCESSFUL


SGA

DatabaseBufferCache

Shared Pool

RedoLogBuffer


DBWR LGWR

PMONSMONCKPT

RollbackSegment

12

Documents

This PowerPoint is based on slides from: Byron Bush, Scott S. Hilpert and Lee, JeongKyu