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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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Questions and Answers