HOT BACKUP

For taking the cold backup the database should be shutdown where as for hot backup there is no need to to shutdown the database.If the organization requires database 24/7 then hot backup is the only choice.

Prerequisites:- 
 1.In order to take the hot backup the archive log should be enabled.
 2.In hot backup control file will be backup at oracle level using a sql statement.
            Alter database backup control file to "location of backup controlfile".
 3.In cold backup we can restore the data but not in the hot backup because hot backup does not contain redolog files.Redologs  are not backed up because they are continuosly getting updated/modified because of transactions.

Whenever we keep our database in begin backup mode our SCN number will be freezed.

[oracle@appsdb ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.1.0 Production on Mon Sep 12 15:54:34 2016

Copyright (c) 1982, 2009, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> select name from v$database;

NAME
---------
SUBBU

SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /u01/app/oracle/arch
Oldest online log sequence     1
Next log sequence to archive   1
Current log sequence           1

SQL> select * from v$backup;

     FILE# STATUS                CHANGE# TIME
---------- ------------------ ---------- ---------
         1 NOT ACTIVE                  0
         2 NOT ACTIVE                  0
         3 NOT ACTIVE                  0
         4 NOT ACTIVE                  0
         5 NOT ACTIVE                  0
         6 NOT ACTIVE                  0

6 rows selected.
Here not active indicates our database is not backup.

SQL> alter database begin backup;

Database altered.

SQL> select * from v$backup;

     FILE# STATUS                CHANGE# TIME
---------- ------------------ ---------- ---------
         1 ACTIVE                 632008 12-SEP-16
         2 ACTIVE                 632008 12-SEP-16
         3 ACTIVE                 632008 12-SEP-16
         4 ACTIVE                 632008 12-SEP-16
         5 ACTIVE                 632008 12-SEP-16
         6 ACTIVE                 632008 12-SEP-16


6 rows selected.