oracle -arch-backup and recovery

8/13/2019 Oracle -Arch-Backup and Recovery

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ORACLE SYSTEM

ADMINISTRATION

TRAININGFOR

LEVEL 2TECHNICAL SUPPORT


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Course Overview

The environment

The architecture

An Oracle Instance

An Oracle Database

How to startup and shutdown the instance Database creation

Database access


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Course Overview

Archive and noarchivelog log mode

Database Backup

Database Recovery

Import and export utilities

Parallel server Questions and Answers


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Environment Variables

ORACLE_HOME

ORACLE_SID

ORACLE_BASE (OPTIONAL)


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Product directory

/oracle//product /rdbms

/admin /sql scripts for data dictionary

/bin

/oracle, oracle0, exp , imp, svrmgrl, sqlplus

/dbs /init.ora, config.ora


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Architecture

The three main components are:

Background processes

Memory structure

Files


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Background Processes

The required processes are:

SMON

PMON

DBWR

LGWR

Other processes are CKPT, ARCH, RECO

Generally, a server process is started for

each user process (connection)


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Memory Structure

This is known as the System Global Area or

SGA

large Pool

The three main components are:

Database Buffer cache

Shared pool/shared SQL area

Library Cache

Dictionary Cache

Redo Log buffer cache


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Files

Parameter files (init.ora & config.ora)

Controlfiles

Datafiles

Redo log files


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Parameter Files

The init.ora file

The config.ora file

They contain configuration information

The default location for the init.ora is in the

/oracle//product/dbs directory

The config.ora file contains instance

specific configuration


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Controlfiles

The control files contains information about

the physical structure and status of the

database

It is a binary file and cannot be viewed

using a text editor

It is critical to the operation of the databaseand must be mirrored to prevent losses due

to media failure


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Data Files

Datafiles are storage area for information

Can be either a flat file or a raw partition


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Redo Log Files

The files contain records of transactions

which modify the data in the database

Each database must have at least two redo

log groups and at least one member in each

group

Is often mirrored for safety reasons


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An Oracle Instance

An instance is made up of the SGA and the

background processes

An instance can be started without opening

a database

It is a framework under which the database

operates


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Starting An Instance

Server manager is used to start an instance

The command to start server manager is

svrmgrl (server manager line mode)

The user connects as internal before

starting the instance if she was

authenticated at the OS level.


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Starting An Instance

The instance is brought up using the startup

command

There are three stages in the startup process:

startup nomount

startup mount

startup open

startup force


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Shutting Down An Instance

This is accomplished through the shutdown

command

The shutdown command accepts threeparameters:

shutdown normal

immediate

abort


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Showing Server Processes

Once an instance is started, use the ps -ef

or ps -ax command to display all the

background processes for that instance Each background process name shown in

the ps output includes the instance name


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Accessing An Instance

Each person is given a login to the instance

System administrator usually does connect

internal or connect / as sysdba

System/manager is the login and password

used for system maintenance activities

Having a login does not mean that the user

has privileges to perform any operations in

the database


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An Oracle Database

A database is composed of one or more

control files, data files and redo log files

Logically, a database is made up of one ormore tablespaces

Typical tablespaces in a database are

system, user, tool, rollback, temporary

A database or a tablespace can be online or

offline


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Database Creation

There is one database per instance but

multiple instances can access the same

physical database (Oracle Parallel Server) The database must have at least one control

file, one data file and two redo log groups

The init.ora file must be edited to includethe name of the database, the block size and

other appropriate parameters


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Creating A Database

Create database command

This command must be executed in the

nomount stage

A control file is created during this process

and it needs to be mirrored

When the database is first created, only the

SYSTEM tablespace exists


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Database File Synchronization

An Oracle database cannot be opened

unless all data, control and redo log files are

synchronized Synchronization is based on the current

redo log sequence number ? SCN numbers

The exception is read-only tablespace


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Database Access

Connecting as internal or sysdba is required

for structural changes

Two logins (sys and system) are reservedfor system maintenance activities

When creating a user, a profile indicating

the resource assigned to the user must bespecified


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Database Access

There are two types of privileges: system

and object

System privileges allow users to performoperations that affect the structure of the

database

Object privileges allow users to performspecific actions on specific objects


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Roles & Permissions

To simplify the granting of privileges, roles

are created

A role can be assigned to multiple users

System and object privileges can be granted

to the role


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Trace File and Alert File

If an error occurs while the Oracle instance

is running, messages are sent to the alert file

If an internal error is detected by a server orbackground process, the information is sent

to a trace file

The BACKGROUND_DUMP_DESTparameter in the init.ora file indicates the

location of both the alert and trace files


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Transaction and Redo Log

When data modification activities occur, the

changes are first written to the redo log

The changes are reflected in the data filesonly if the transaction has been committed

A database must have at least two redo log

groups

Oracle writes to the redo log groups in a

circular fashion


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Noarchivelog Mode

During the database creation process, the

default mode is noarchivelog unless the

archivelog parameter is explicitly specified This means that when Oracle has filled up

all the redo log groups, it will reuse them by

writing over existing information


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Archivelog Mode

In the archivelog mode, the redo log files

are not reused until the ARCH process has

made a copy of the content of file The archived log files will be used for

recovery from media failure


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Archivelog Mode

The archivelog mode is enabled by issuing

the alter database archivelog command

Archiving redo logs can be automatic ormanual

To start archiving the redo log manually,

issue the alter system archive log start (thistell the ARCH process to begin archiving)


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Archivelog Mode

For automatic archiving, change the

following init.ora parameters:

LOG_ARCHIVE_START = true

LOG_ARCHIVE_FORMAT = filename and

extension

LOG_ARCHIVE_DEST = directory path andfile prefix


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Database Backup

When developing a Backup strategy for a

database, the following items need to be

considered: the tolerance level for loss of data

the amount of time available for backups

the mode of the database


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Database Backup

In the noarchivelog mode, the database

must be offline prior to taking backup (this

is known as cold backups) In the archivelog mode, the database can be

online during the backup (this is known as

hot backups)


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Database Backup

The scope of a backup can be full or partial

An offline (cold) backup is always a full

database backup

An online (hot) backup can be full or partial

In a partial hot backup, only selected

tablespaces are backed up or anything less

than a full database backup


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Offline (Cold) Backup

Steps required are:

Query the database to find out the data, control

and redo log files to be backed up Shutdown the instance using shutdown normal

or immediate

Use operating system commands to make acopy of all the files

The parameter files should also be backed up


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Offline (Cold) Backup

The main advantage of cold backups is ease

of operation

The main disadvantages are: Database unavailable during backup

Possible loss of data


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Online (Hot) Backup

Steps required are:

Query the database to find out the tablespaces

to be backed up Tablespaces are put into the backup mode using

the Alter tablespace begin

backup; command

Use operating system commands to make a

copy of all the datafiles for each tablespace

Take the tablespace out of the backup mode

using the alter tablespace


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Online (Hot) Backup

Advantages of hot backups are:

Prevent loss of data

Database available during backup

Allow more flexible recovery options

The main disadvantage is that recovery

from this type of backup may becomplicated


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Control File Backup

The command to back up the control file is:

alter database backup controlfile to ;

alter database backup controlfile to/db2/oracle/KENL/backup/control01.ctl

The control file can be dumped in the text

format as follow: alter database backup controlfile to trace;

Recommended after any changes to the

database structure


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Backup of Read-Only Tablespace

Data files related to the read-only

tablespace need to be backed up only once

The status of these tablespaces isunimportant


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Database Recovery

Recovery strategies depend on the cause of

failure and the mode of the database

For instance failure or crash recovery,Oracle will automatically perform instance

recovery during the next startup -SMON

For media failure, the affected files must berestored manually and the database needs to

be recovered


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Database Recovery

For databases in noarchivelog mode,

complete database recovery is the only

option For databases in archivelog mode, both

complete and incomplete recoveries are

permitted


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Recovery Process

There are three phases in the recovery

process:

Identified what needs to be restored File restoration

Application of redo and archive logs

All transactions are applied to the databasethen uncommitted ones are rolled back to

bring the database to a consistent state


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Recovery Process

Oracle will prompt the user to confirm

before applying each archived log file

This process can be automated by settingautorecovery on before recovering the

database or enter AUTO at the prompt

If the archived log files are not in thedefault location, specify the new location

and filenames when prompted


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Recovery from Cold Backups

Steps required are:

Replace all existing data, control and redo log

files with those from the backup Replace the parameter files if necessary

Start the instance

The entire database will be brought back tothe time of the backup


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Recovery from Hot Backups

Recovery from a hot backup can be

complete or incomplete

Complete recovery is a recovery of thedatabase/tablespace/data file to the point of

failure

Incomplete recovery happens when thedatabase is not recovered to the point of

failure


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Complete Recovery

Tablespaces and datafiles cannot be

recovered to a point in time in the past

while leaving the rest of the database in thecurrent time

Tablespaces and data files must be taken

offline before performing the recovery


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Incomplete Recovery

There are four types of incomplete

recovery: time based, change based, cancel

based and using a backup control file In order to perform incomplete recovery,

the database has to be in archivelog mode

The database must be opened with theresetlogs parameter


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Point-In-Time Recovery

This is done using the recover database

command with the until clause

The user can specify a particular time or aspecific SCN number

The database must be opened with the

resetlogs option and all previous backupsbecome invalid


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Recovering Control File

If there are good copies of the control file,

shutdown the instance and copy the good

one over the damaged one and restart theinstance

Otherwise, recover the control file from the

backup


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Recreating the Control File

Required if all the control files are damaged

and there is no good backup or if the

database name changes Use the create control file command

The trace dump of the control file can be

edited and used to create a new one alter database backup controlfile to trace;

create a trace file in udump (location specified

in your init.ora) destination

R i R d O l


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Recovering Read-Only

Tablespace

Read-only tablespaces are ignored during

database recovery

However, if the data files for this type oftablespace become damaged, replace them

with those from the backup


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Import and Export

Import and export are utilities used to

perform logical backup and recovery of the

database or individual objects The information is written to operating

system files

export file has .dmp extention by default The export files can be used to move data

between machines and versions of Oracle

even with full exp, all the objects owned by


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Export

Scope of the export can be the whole

database, the tables or objects, or objects

belonged to a user or schema There are three types of export: complete,

incremental and cumulative


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Import

The import utility can only import files

created by the export utility

There are three types of information thatcan be imported: table definition, table data

and table constraints

The order in which objects are imported isimportant (referential integrity)


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Oracle Parallel Server

The Oracle server can run in either the

exclusive or shared (parallel) mode

In the shared mode, one or more instancesof the server access a single physical

database

Each instance has its own SID, SGA,parameter file, background processes and

redo log files


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Oracle Parallel Server

All instances share the same data files and

control files

Additional background processes, LCKn,are required to coordinate the locking of

shared resources


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