Question { 4543 }

What does LGWR do?

Answer

Whenever any change takes place in database,first the change is written to LOGBUFFER.Then from LOGBUFFER the changes are written to REDOLOG files.
LogWriter(LGWR) is a process that writes the redobuffers from LOGBUFFER to REDOLOGFILES in terms on change vectors.

When does Logwriter(LGWR) writes to Redologs,
-Whenever logbuffer is 1mb or 1/3rd full.
-Whenever user commits.

Question { 5094 }

How to implement the multiple control files for an existing
database ?

Answer

1)Check number of controlfiles.
SQL>select name from v$controlfile.
Suppose there are two controlfiles,control01.ctl and control02.ctl.Check the path of controlfiles.
SQL>Shut immediate.
Go to the controfile location.
$ls
control01.ctl control02.ctl
$cp control01.ctl control03.ctl
$ls
control01.ctl control02.ctl control03.ctl

Now open parameter file init.ora .
$vi init.ora
control_files='/home/..../control01.ctl','/home/.../control02.ctl','/home/...../control03.ctl'

save and quit
SQL>startup
SQL>Now check the name and path of controfiles.

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Question { 5370 }

What is a Control file ?

Answer

Cotrolfile is physical file that contains information regarding database physical structure and modes of database.
It is in binary format.
It has two sections.1.Non-reusable section
2.Reusable Section
Controlfile generally contains,
-Database name
-Timestamp of database creation
-System Change number(SCN)
-Logs History
-Names and path of datafiles
-Tablespace offline status
-Checkpoint number
One section of controlfiles reserved for RMAN backups,controlled by the parameter control_file_keep_record_time=7(days).

Question { GE, 23640 }

Can you take Online Backups if the the database is running
in NOARCHIVELOG mode?

5. How do you bring the database in ARCHIVELOG mode from
NOARCHIVELOG mode?

6. You cannot shutdown the database for even some minutes,
then in which mode you should run
the database?

Answer

No.We cannot take Online Backups if the database is running in NOARCHIVELOG mode.

Steps To bring database in ArchiveLog Mode.

1)Shut down the database if running.
2)Open Parameter file and set the following parameter
LOG_ARCHIVE_DEST='Path to where Archivelog has to be stored'

Then Save the parameter file

3)Now open the database in Mount Stage

To Check the mode of database:
SQL>select log_mode from v$database;

NoArchiveLog

Now to Enable ArchiveLog

SQL>alter database archivelog;
SQL>Select log_mode from v$database;
4)Open the database .

To know the archive log destination and Status of RedoLogs,
SQL>archive log list