Begain backup concepts

Following internal operations happened with immediate effect after triggering begin backup for tablespace

1. Partial check point (for all blocks part of the subjected tablespace)
2. Headers of datafiles would be freeze while datafile blocks would be available for normal access
3. The first time a block is changed in a datafile that is in hot backup mode, the entire block is written to the redo log files, not just the change vector. Normally only the changed bytes (a change vector) are written. In hot backup mode, the entire block is logged the first time (successive updates against that block would be logged as usual change vector only). This is because you can get into a situation where the process copying the datafile and DBWR are working on the same block simultaneously.
4. The datafile headers which contain the SCN of the last completed checkpoint are not updated while a file is in hot backup mode. This lets the recovery process understand what archive redo log files might be needed to fully recover this file.
5. Once you end backup the datafile headers would be unfreeze and synced with current SCN from control file.
let's confirm that the datafile header freeze  during hot backup

SQL> alter database begin backup;

alter database begin backup

*

ERROR at line 1:

ORA-01123: cannot start online backup; media recovery not enabled

Alter database begin backup ;

!cp /home/oracle/10.2.0/product/oradata/orcl/users01.dbf   /home/oracle/backup/users01.dbf

!cp /home/oracle/10.2.0/product/oradata/orcl/sysaux01.dbf   /home/oracle/backup/sysaux01.dbf

!cp /home/oracle/10.2.0/product/oradata/orcl/undotbs01.dbf  /home/oracle/backup/undotbs01.dbf

!cp /home/oracle/10.2.0/product/oradata/orcl/system01.dbf   /home/oracle/backup/system01.dbf

!cp /home/oracle/10.2.0/product/oradata/orcl/example01.dbf   /home/oracle/backup/example01.dbf

!cp /home/oracle/10.2.0/product/oradata/orcl/mytbs.dbf      /home/oracle/backup/mytbs.dbf

  

Can check  datafile backup status using below view

SQL>  select file#,status from v$backup;

     FILE# STATUS

---------- ------------------

         1      ACTIVE

         2      ACTIVE

         3      ACTIVE

         4      ACTIVE

         5      ACTIVE

         6      ACTIVE

6 rows selected.

 Now we connect to the user and run insert statement 

SQL> conn scott/tiger

Connected.

SQL> insert into abc select * from abc;

809232 rows created.

SQL> commit;

check the CHECKPOINT_CHANGE# from v$datafile_header

SQL>  select CREATION_CHANGE#, RESETLOGS_CHANGE#,CHECKPOINT_CHANGE# from v$datafile_header;

CREATION_CHANGE# RESETLOGS_CHANGE# CHECKPOINT_CHANGE#

---------------- ----------------- ------------------

               8            525876            1730264

          523586            525876            1730264

            6294            525876            1730264

           10169            525876            1730264

          547523            525876            1730264

         1720920            525876            1730264

6 rows selected.

SQL> alter system checkpoint;

System altered.

Check the CHECKPOINT_CHANGE# from v$datafile_header after fired checkpoint manually  but it's still same.

SQL>  select CREATION_CHANGE#, RESETLOGS_CHANGE#,CHECKPOINT_CHANGE# from v$datafile_header;

CREATION_CHANGE# RESETLOGS_CHANGE# CHECKPOINT_CHANGE#

---------------- ----------------- ------------------

               8            525876            1730264

          523586            525876            1730264

            6294            525876            1730264

           10169            525876            1730264

          547523            525876            1730264

         1720920            525876            1730264

6 rows selected.

SQL> alter system switch logfile;

System altered.

SQL> alter system checkpoint;

System altered.

SQL>  select CREATION_CHANGE#, RESETLOGS_CHANGE#,CHECKPOINT_CHANGE# from v$datafile_header;

CREATION_CHANGE# RESETLOGS_CHANGE# CHECKPOINT_CHANGE#

---------------- ----------------- ------------------

               8            525876            1730264

          523586            525876            1730264

            6294            525876            1730264

           10169            525876            1730264

          547523            525876            1730264

         1720920            525876            1730264

6 rows selected.

SQL> alter system checkpoint;

System altered.

Again we verified the  CHECKPOINT_CHANGE#   after fire checkpoint manually  but there is no change .

SQL>  select CREATION_CHANGE#, RESETLOGS_CHANGE#,CHECKPOINT_CHANGE# from v$datafile_header;

CREATION_CHANGE# RESETLOGS_CHANGE# CHECKPOINT_CHANGE#

---------------- ----------------- ------------------

               8            525876            1730264

          523586            525876            1730264

            6294            525876            1730264

           10169            525876            1730264

          547523            525876            1730264

         1720920            525876            1730264

6 rows selected.

After end backup when I chek again  now CREATION_CHANGE#  has been changed .

SQL> select CREATION_CHANGE#, RESETLOGS_CHANGE#,CHECKPOINT_CHANGE# from v$datafile_header;

CREATION_CHANGE# RESETLOGS_CHANGE# CHECKPOINT_CHANGE#

---------------- ----------------- ------------------

               8            525876            1736138

          523586            525876            1736138

            6294            525876            1736138

           10169            525876            1736138

          547523            525876            1736138

         1720920            525876            1736138

6 rows selected.