INTRODUCTION ============ This article discusses the most common concepts of backup and recovery of the Oracle database. This article discusses physical backups and not logical backups. (An export of the database is an example of a logical backup.) Why do we need backups? ====================== The most important responsibility of a database administrator is to prepare for the possibility of media, hardware and software failure. Should any of these failures occur the major goal is to make the database available to users within an acceptable time, ensuring that committed data is undamaged. This paper discusses only physical backups and not logical backups. An export of the database is an example of a logical backup. What are the things that go wrong and eventually lead to recovery? ================================================================= One or more database files are damaged. One or more redo log files (including online) are damaged.
INTRODUCTION============This article discusses the most common
concepts of backup andrecovery of the Oracle database.This article
discusses physical backups and not loical backups.!"n e#port of the
database is an e#ample of a loical backup.$%hy do &e need
backups'======================The most important responsibility of
a database administrator is toprepare for the possibility of media(
hard&are and soft&are failure.)hould any of these failures
occur the ma*or oal is to make thedatabase available to users
&ithin an acceptable time( ensurinthat committed data is
undamaed.This paper discusses only physical backups and not loical
backups."n e#port of the database is an e#ample of a loical
backup.%hat are the thins that o &ron and eventually lead to
recovery'=================================================================One
or more database +les are damaed.One or more redo lo +les !includin
online$ are damaed.One or all control +les are damaed.%hat is
recovery'================Restorin the +les from backup and rollin
for&ard in time is R,CO-,R.."N INT,RN"/
-I,%================)ome admnistrative actions can destroy a
database beyond repair. This isparticularly true of backup and
recovery commands. To understand thedaners of certain commands( a
database administrator should have aood understandin of the
contents and purpose of the control +le(data+les and lo +les. The
basics are provided here.Control +le============" control +le
re0ects the structure of a database at particular pointsin time. It
contains the checkpoint information( names of lo +lesand data +les(
header information of the +les and lo se1uence number(&hich is
very important for recovery purposes. The recovery is doneonly by
applyin the lo +les &hose se1uence number is reater thanlo
se1uence number in the control +le.Data+le information in control
+le23333333333333333333333333333333333333 Names of data+les and lo
+les &ith e#act path.3 4ile si5e.3 6lock si5e.!Oracle block
si5e$3 %hether the data+le is online or o7ine.3 %hether the data+le
&as taken o7ine automatically or not.3 %hether the data+le
belons to the system tablespace or not.3 ,ntry for each data+le
ivin a lo se1uence number &hen tablespace&as taken o7ine./o
+le information in control
+le23333333333333333333333333333333333333 Name &ith e#act
path.3 4ile si5e.3 6lock si5e. !O8) block si5e$3 /o se1uence93 :as
the +le been archived.Information in the data+le
header==================================3 /o se1uence number of
ne#t lo +le that could be applied.3 %hether online backup in
proress.Information in the lo +le
header==================================3 /o se1uence93 "rchival
information.6"C;U?3hours per day and &hen it isnot feasible to
take o7ine backups( then an alternative is providedby Oracle
&here physical backups are performed &hile the database
remainsavailable for both readin and updatin. 4or this kind of
backup thedatabase must be in "RC:I-,/O= mode. Only data +les and
currentcontrol +le need to be backed up. Unlike o7ine backups( the
unit ofa online backup is a tablespace( and any or all tablespaces
can backedup &henever needed. Di@erent data+les can be backed
up at di@erenttimes.
