Showing posts with label database. Show all posts
Showing posts with label database. Show all posts

Thursday, 19 April 2018

How to create Oracle directory?

Database Directories are required to read/write to a filesystem location from plsql code.

Below is the syntax to create database directory

SQL> create directory PLSQL_DIR AS '/oratmp/code';

Directory created.

Grant Read/write privileges to Required Schema


Grant succeeded.

Oracle Recovery Manager Troubleshooting ::ORA-27211: Failed to load Media Management Library

This is an error during Database Clone using RMAN.

I was trying to restore database using RMAN Backup

RMAN-00571: ===========================================================

RMAN-00569: ===============

RMAN-00571: ===========================================================

RMAN-03002: failure of Duplicate Db command
RMAN-05501: aborting duplication of target database

RMAN-03009: failure of allocate command on ORA_AUX_SBT_TAPE_1 channel 
ORA-19554: error allocating device, device type: SBT_TAPE, device name:

ORA-27211: Failed to load Media Management Library

Additional information: 

Cause: Backup Configuration was modified.

Use the below command to Resolve the error and continue with Database Restore

rman auxiliary / 
allocate auxiliary channel c1 type disk;
allocate auxiliary channel c2 type disk;
duplicate database to 'DEV' backup location '/Daily_Backup/Backup_16042018';

Friday, 13 April 2018

Oracle Database Recovery Manager Concepts:Script to Restore Oracle Database from RMAN Backup

During Oracle Database Cloning,restore Oracle database from RMAN backup taken on Source environment to the Target environment.

Steps for Database restore using Oracle Recovery Manager (RMAN)

1.Connect to target database 

Startup the Target database in Nomount stage

SQL> Startup nomount

2.Run the below Command to Restore Oracle database using RMAN 

rman auxiliary / 
duplicate database to 'DEV' backup location '/DB_BACKUP/Daily_Backup/daily_bkp_04102018';

Where DEV is the target instance for Restore
Backup Location - Directory where RMAN backup is located

3. Verify that Oracle database is up and running.

Resolve ORA-28545 When trying to access database link between Oracle database and MSSQL

Heterogenous database link between Oracle database and MSSQL was created using the below command.

SQL> create public database link mssql connect to "integration" identified by "*****" using 'dg4msql'; 

Database link created. 

Error Message

SQL> select sysdate from dual@mssql 
2 ; 
select sysdate from dual@mssql 

ERROR at line 1: 
ORA-28545: error diagnosed by Net8 when connecting to an agent 
Unable to retrieve text of NETWORK/NCR message 65535 
ORA-02063: preceding 2 lines from MSSQL 

(ADDRESS = (PROTOCOL = TCP)(HOST = oraclegtwy.dmn)(PORT = 1526)) 


Listener file on the Oracle Database gateway server should look like below 

(ADDRESS = (PROTOCOL = TCP)(HOST =oraclegtwy.dmn)(PORT = 1526)) 

SID_LIST_LISTENER_GTWY =------------------------>Missing 

Saturday, 7 April 2018

Command to check LUN details on a Linux server

Logical Unit Number (LUN) is part of Storage Management in Oracle Automated Storage Management (ASM).

Below command is useful to check the available LUN's on a linux server.

As root user,

Run the command ls -la /dev/disk/by-id/  

Sample Output below:

[root@erptestdb ~]# ls -la /dev/disk/by-id/
total 0
drwxr-xr-x 2 root root 240 Jan 29 16:17 .
drwxr-xr-x 6 root root 120 Jan 29  2018 ..
lrwxrwxrwx 1 root root   9 Jan 29  2018 scsi-3******************************** -> ../../sdd
lrwxrwxrwx 1 root root  10 Jan 29 15:40 scsi-3********************************-part1 -> ../../sdd1
lrwxrwxrwx 1 root root   9 Jan 29  2018 scsi-3******************************** -> ../../sdf
lrwxrwxrwx 1 root root  10 Jan 29 16:17 scsi-3********************************-part1 -> ../../sdf1
lrwxrwxrwx 1 root root   9 Jan 29  2018 scsi-3******************************** -> ../../sdc
lrwxrwxrwx 1 root root  10 Jan 29 15:40 scsi-3********************************-part1 -> ../../sdc1
lrwxrwxrwx 1 root root   9 Jan 29  2018 scsi-3********************************-> ../../sdb
lrwxrwxrwx 1 root root  10 Jan 29 15:40 scsi-3********************************-part1 -> ../../sdb1
lrwxrwxrwx 1 root root   9 Jan 29  2018 scsi-3******************************** -> ../../sde
lrwxrwxrwx 1 root root  10 Jan 29 15:40 scsi-3********************************-part1 -> ../../sde1
[root@erptestdb ~]#

Sunday, 6 August 2017

What is Edition Based Redefinition (EBR) in Oracle?

Edition Based Redefinition (EBR) is a new feature introduced from Oracle Software Version 11g R2.Edition-based redefinition allows multiple versions of PL/SQL objects, views and synonyms in a single schema.This feature facilitates Online patching of database objects in R12.2 online Patching.

Editionable and Non-editionable Objects

Below schema object types are editionable in the database:

SQL translation profile

All PL/SQL object types:


If a schema object type is editionable in the database, then it can be editionable in schemas.All other schema object types are noneditionable in the database and in every schema, and objects of that type are always noneditioned. Tables are always noneditioned objects.

To view the editions related information in the database, use the below datadictionary tables.


DBA_OBJECTS_AE: DBA_OBJECTS_AE view shows all objects, of all editions.

What is the use of MMON background process in Oracle Database?

MMON (Manageability Monitor)

MMON (Manageability Monitor) is a background process introduced in Oracle 10g. It gathers memory statistics (snapshots) and stores this information in the AWR (automatic workload repository). MMON is also responsible for issuing alerts for metrics that exceed their thresholds.

Tuesday, 25 July 2017

Oracle Recovery Manager Features: BACKUP AS COPY

What is the advantage backup as copy feature in RMAN?

RMAN(Recovery Manager) utility creates backup in the form of backupsets or backup pieces by default.RMAN utility also allows other method which is similar to user managed hot backup. It can be acheived using 'BACKUP AS COPY' command.Using "Backup as Copy" RMAN creates backup in the form of image copies. However, we do not need to put the database in begin backup/end backup mode as in Conventional Hot Backup.

Syntax for Datafile Backup using Backup as copy:

RMAN> backup as copy datafile 1 format '/backup/data/datafile01.dbf' ;

Another advantage of this feature is that it allows to create image copy of control file.

 RMAN> backup as copy current controlfile format 'F:\CntrlFile_Bkp.ctl';  

How do we identify backups taken  as Image copies using RMAN?

Use "LIST COPY" Command. "LIST BACKUP" only gives a list of backup sets which were created using default RMAN backup Methos.



Thursday, 6 July 2017

How to Configure RMAN Backups into Multiple Locations?

If we need  RMAN to distribute backup sets among multiple disks on different mountpoints. We can use the below syntax to configure backup in multiple locations.

Using Allocate Channel:


Using Configure Channel:


Tuesday, 27 June 2017

Oracle RMAN (Recovery Manager) Concepts

What is the difference between obsolete and expired Backup in RMAN?

Obsolete Backup: Backup pieces or backup sets which are not needed for recovery.
We can use the REPORT OBSOLETE command to list the obsolete backups and DELETE OBSOLETE command to delete the obsolete backup.

Expired Backup:When the CROSSCHECK command is used to determine whether backups recorded in the repository still exist on disk or tape, if RMAN cannot locate the backups, then it updates their records in the RMAN repository to EXPIRED status.We can then use the DELETE EXPIRED command to remove records of expired backups from the RMAN repository.

Oracle DBA Concepts: Background Processes in Oracle ASM (Automatic storage Management)

The following background processes are an integral part of Automatic Storage Management:

ARBn performs the actual rebalance data extent movements in an Automatic Storage Management instance. There can be many of these processes running at a time, named ARB0, ARB1, and so on.

ASMB runs in a database instance that is using an ASM disk group. ASMB communicates with the ASM instance, managing storage and providing statistics. ASMB can also run in the ASM instance. ASMB runs in ASM instances when the ASMCMD cp command runs or when the database instance first starts if the SPFILE is stored in ASM.

GMON maintains disk membership in ASM disk groups.

MARK marks ASM allocation units as stale following a missed write to an offline disk. This essentially tracks which extents require resync for offline disks.

RBAL runs in both database and ASM instances. In the database instance, it does a global open of ASM disks. In an ASM instance, it also coordinates rebalance activity for disk groups.

Sunday, 25 June 2017

How to change Rebalance Power in ASM Instances?

Whenever a new diskgroup is added or dropped, ASM automatically performs REBALANCING operation.Power used by rebalacing defaults to value specified for asm_power_limit initialization parameter.We can check the status of rebalancing from v$asm_operation view.

Increasing the value of ASM_POWER_LIMIT, reduces the estimated time for completion of Rebalance Operation.

ASM power limit can be increased using the below command

alter system set asm_power_limit =11;

To know more about values for this parameter, check this link:

But this does not increase the rebalancing power of current operation. 

To increase the rebalancing power of ongoing operation, use the below command

 alter diskgroup dg1 rebalance power 11;

We can also specify rebalance power at the time of adding or dropping disks.

alter diskgroup dg1 add disk d01 rebalance power 11;

When to use asm_power_limit 0?

Whenever there is a need to add/drop several disks (like migrations), setting the power limit to 0 is highly beneficial.We can avoid the waiting time for rebalance operation to complete,before the next disk is rebalanced.In such cases, set the asm_power_limit to 0, add/drop all the disks and set the value of asm_power_limit to a non zero value.
Rebalance operation will be parallelized and completes faster.

Oracle Database ASM Features: REBALANCING

ASM has the ability to rebalance data across the disks whenever a disk is added,dropped or replaced.
The performance of rebalance operation is controlled by initialization parameter ASM_POWER_LIMIT.


Default value 1

Range of Values 0 to 11 (Prior to 11gR2)

Range of Values 0 to 1024(From 11gR2)

For 10g Databases:

SQL> alter diskgroup DG1 rebalance power 12;

alter diskgroup DG1 rebalance power 12
ERROR at line 1:
ORA-15102: invalid POWER expression

SQL> alter diskgroup DG1 rebalance power 11;

Diskgroup altered.

For 11g AND 12c Databases

SQL> alter diskgroup DG1 rebalance power 1025;
alter diskgroup DG1 rebalance power 1025
ERROR at line 1:
ORA-15102: invalid POWER expression

SQL> alter diskgroup DG1 rebalance power 1024;

Diskgroup altered.

The higher the value of rebalancing power, faster would be rebalancing operation.

Tuesday, 6 June 2017

Initialization Parameters Required for Oracle ASM (Automatic Storage Management)

The below parameters are required for ASM instance.


INSTANCE_TYPE specifies whether the instance is a database instance or an Automatic Storage Management instance.



The instance is a database instance.


The instance is an Automatic Storage Management instance.


DB_UNIQUE_NAME specifies a globally unique name for the database

Default value
Database instances: the value of DB_NAME
Automatic Storage Management instances: +ASM


ASM_POWER_LIMIT specifies the maximum power on an Automatic Storage Management instance for disk rebalancing. The higher the limit, the faster rebalancing will complete. Lower values will take longer, but consume fewer processing and I/O resources.

Default value 1

Range of Values 0 to 11 (Prior to 11gR2)

Range of Values 0 to 1024(From 11gR2)


ASM_DISKGROUPS specifies a list of names of disk groups to be mounted by an Automatic Storage Management instance at instance startup or when an ALTER DISKGROUP ALL MOUNT statement is issued.

Automatic Storage Management (ASM) automatically adds a disk group to this parameter when the disk group is successfully created or mounted, and automatically removes a disk group from this parameter when the disk group is dropped or dismounted.

Issuing the ALTER DISKGROUP...ALL MOUNT or ALTER DISKGROUP...ALL DISMOUNT command does not affect the value of this parameter.


ASM_DISKSTRING specifies an operating system-dependent value used by Automatic Storage Management to limit the set of disks considered for discovery. When a new disk is added to a disk group, each Automatic Storage Management instance that has the disk group mounted must be able to discover the new disk using the value of ASM_DISKSTRING.


ASM_PREFERRED_READ_FAILURE_GROUPS specifies the failure groups that contain preferred read disks. Preferred disks are instance specific. This parameter is only valid in ASM instances.

Tuesday, 23 May 2017

SQL Profile and SQL Plan Baseline

What is SQL Profile?

A SQL profile contains corrections for poor optimizer estimates discovered by the SQL Tuning advisor.A  SQL profile is to a SQL statement what statistics are to a table or index.
Implementing sql profiles allows us to replace bad sql execution plan with good execution plan.

What is SQL Plan Baseline?

A SQL plan baseline for a SQL statement consists of a set of accepted plans. When the statement is parsed, the optimizer will only select the best plan from among this set. If a different plan is found using the normal cost-based selection process, the optimizer will add it to the plan history but this plan will not be used until it is verified to perform better than the existing accepted plan and is evolved.

Friday, 5 May 2017

Oracle Database Administrator Interview Questions on RAC

Oracle RAC (Voting Disk ) FAQ's

1.What is Voting Disk?

Voting Disk is a file that maintains node membership details.
All members in the Cluster read and write Heartbeat Information in Voting Disk.

2. What Information is stored in Voting Disk?

Voting disks contain static and dynamic data.
Static data : Info about nodes in the cluster
Dynamic data : Disk heartbeat logging
It maintains and consists of important details about the cluster nodes membership, such as
- which node is part of the cluster,
- which node is joining the cluster, and
- which node is leaving the cluster.

3. Why do we need Voting Disk?

CSSD processes (Cluster Services Synchronization Daemon) monitor the health of  RAC nodes employing two distinct heart 

beats: Network heart beat and Disk heart beat. Healthy nodes will have continuous network and disk heartbeats exchanged 

between the  nodes. Break in heart beat indicates a possible error scenario. There are few different scenarios possible 

with missing heart beats:
1. Network heart beat is successful, but disk heart beat is missed.
2. Disk heart beat is successful, but network heart beat is missed.
3. Both heart beats failed.
In addition, with numerous nodes, there are other possible scenarios too. Few possible scenarios:
1. Nodes have split in to N sets of nodes, communicating within the set, but not with members in other set.
2. Just one node is unhealthy.
Nodes with quorum will maintain active membership of the cluster and other node(s) will be fenced/rebooted.

4.Why do we have odd number of voting disks?

Odd number of Voting disks are required to prevent Split Brain Syndrome.
A node must be able to access more than half of the voting disks in order to decide which node can be evicted incase of 


5. How to backup Voting Disk?

Prior to Oracle 11g R2 version, Voting Disk is backed up using dd command

From 11g R2, no need to manually backup voting disk.
It is automatically backup along with OCR  whenever there is a configuration change.

In 11g R2, Restoring Voting disk from a manually copied backupfile may prevent cluster services from starting up.

Friday, 30 December 2016

What is OCR (Oracle Cluster Registry)?

Oracle Cluster Registry

OCR is the central repository for the Oracle cluster.
OCR has information about Port information,node failures, node reconfiguration,Database Status,Listener Status,Instance status, Network Status in real time.

Default Location of ocr.loc file on linux --  /etc/oracle/ocr.loc

Oracle Clusterware reads ocr.loc to determine the registry information and application resources that need to started up on each cluster node.

The below processes update OCR with realtime information.

1. CRSd updates  OCR with  information about node failure 
2. CSSd updates the OCR when a node is added or deleted
3. NetCA, DBCA, SRVCTL updates  OCR with  services related information

OCR also has information about  Software active version

Software  version can also be found using below command
$ crsctl query crs activeversion

OCR Backup and Restore

OCR is a binary file and cannot be edited manually.By Default, OCR is backed up automatically every 4 hours (from Instance Startup time).
OCR backups are cached across all nodes of a cluster.However,Only Master RAC node can write to OCR.
OCR backups are overwritten automatically. Clusterware maintains last 3 backups of OCR. 

Backup location can be defined using the below command.

$ocrconfig -backuploc <backup location>

It is recommended to use shared location for storing OCR backups.

To view the current OCR backups available, use the below commands

$ocrconfig –showbackup auto 

$ocrconfig –showbackup manual

After any clusterware related changes, OCR backup can be taken manually.

$ocrconfig –manualbackup

If OCR file is Corrupted or lost, CRS Instance may crash.

To restore OCR from Backup,follow the procedure below

1.Using ocrconfig identify the latest OCR backup using command below

$ocrconfig -showbackup
2.Shutdown CRS Services on all RAC nodes
$crsctl stop crs
3.Start CRS on one node in exclusive mode
$crsctl start crs -excl 
Stop crsd , if it is running

$ crsctl stop resource ora.crsd -init

4.Restore the OCR 
$ocrconfig –restore <backuplocation/backupfilename>
5. Verify the integrity of OCR
6. Shutdown  CRS Services on the node where you had started in exclusive mode
$crsctl stop crs 

7.Start CRS on all RAC nodes 
$crsctl start crs
8. Verify the restored OCR 
$cluvfy comp ocr –n all -verbose

Monday, 23 May 2016

"lsnrctl: symbol lookup error: lsnrctl: undefined symbol: nlgh" while starting Oracle Database listener

After Applying PSU, database listener failed to start with below error

 $ lsnrctl start testdb
lsnrctl: symbol lookup error: lsnrctl: undefined symbol: nlgh

1.Relink network executables using below command

$  make -kf install
/bin/chmod 755 /testdb/oracle/product/11204/bin/
 - Linking tnslsnr
rm -f tnslsnr
gcc -o tnslsnr -m64 -z noexecstack -L/testdb/oracle/product/11204/network/lib/ -L/testdb/oracle/product/11204/lib/ -L/testdb/oracle/product/11204/lib/stubs/  /testdb/oracle/product/11204/network/lib/s0nsgl.o /testdb/oracle/product/11204/network/lib/snsglp.o -lclntsh  `cat /testdb/oracle/product/11204/lib/ldflags`    -lncrypt11 -lnsgr11 -lnzjs11 -ln11 -lnl11 -lnro11 `cat /testdb/oracle/product/11204/lib/ldflags`    -lncrypt11 -lnsgr11 -lnzjs11 -ln11 -lnl11 -lnnz11 -lzt11 -lztkg11 -lclient11 -lnnetd11  -lvsn11 -lcommon11 -lgeneric11 -lmm -lsnls11 -lnls11  -lcore11 -lsnls11 -lnls11 -lcore11 -lsnls11 -lnls11 -lxml11 -lcore11 -lunls11 -lsnls11 -lnls11 -lcore11 -lnls11 `cat /testdb/oracle/product/11204/lib/ldflags`    -lncrypt11 -lnsgr11 -lnzjs11 -ln11 -lnl11 -lnro11 `cat /testdb/oracle/product/11204/lib/ldflags`    -lncrypt11 -lnsgr11 -lnzjs11 -ln11 -lnl11 -lclient11 -lnnetd11  -lvsn11 -lcommon11 -lgeneric11   -lsnls11 -lnls11  -lcore11 -lsnls11 -lnls11 -lcore11 -lsnls11 -lnls11 -lxml11 -lcore11 -lunls11 -lsnls11 -lnls11 -lcore11 -lnls11 -lclient11 -lnnetd11  -lvsn11 -lcommon11 -lgeneric11 -lsnls11 -lnls11  -lcore11 -lsnls11 -lnls11 -lcore11 -lsnls11 -lnls11 -lxml11 -lcore11 -lunls11 -lsnls11 -lnls11 -lcore11 -lnls11   `cat /testdb/oracle/product/11204/lib/sysliblist` -Wl,-rpath,/testdb/oracle/product/11204/lib -lm    `cat /testdb/oracle/product/11204/lib/sysliblist` -ldl -lm   -L/testdb/oracle/product/11204/lib -lons -lnl11  -ln11 -lnlsnr11 -lnlsnrc11 -lnsgr11 -lnms -lncm11 -lnmsp -lpeer -lnro11 -ln11   -lnl11 -lnlsnr11 -lnlsnrc11 -lnms -lncm11 -lnmsp -ln11     -lm
mv -f /testdb/oracle/product/11204/bin/tnslsnr /testdb/oracle/product/11204/bin/tnslsnr0
mv tnslsnr /testdb/oracle/product/11204/bin/tnslsnr
/bin/chmod 751 /testdb/oracle/product/11204/bin/tnslsnr
 - Linking lsnrctl
rm -f lsnrctl
gcc -o lsnrctl -m64 -z noexecstack -L/testdb/oracle/product/11204/network/lib/ -L/testdb/oracle/product/11204/lib/ -L/testdb/oracle/product/11204/lib/stubs/  /testdb/oracle/product/11204/network/lib/s0nsglc.o -lclntsh  `cat /testdb/oracle/product/11204/lib/ldflags`    -lncrypt11 -lnsgr11 -lnzjs11 -ln11 -lnl11 -lnro11 `cat /testdb/oracle/product/11204/lib/ldflags`    -lncrypt11 -lnsgr11 -lnzjs11 -ln11 -lnl11 -lnnz11 -lzt11 -lztkg11 -lclient11 -lnnetd11  -lvsn11 -lcommon11 -lgeneric11 -lmm -lsnls11 -lnls11  -lcore11 -lsnls11 -lnls11 -lcore11 -lsnls11 -lnls11 -lxml11 -lcore11 -lunls11 -lsnls11 -lnls11 -lcore11 -lnls11 `cat /testdb/oracle/product/11204/lib/ldflags`    -lncrypt11 -lnsgr11 -lnzjs11 -ln11 -lnl11 -lnro11 `cat /testdb/oracle/product/11204/lib/ldflags`    -lncrypt11 -lnsgr11 -lnzjs11 -ln11 -lnl11 -lclient11 -lnnetd11  -lvsn11 -lcommon11 -lgeneric11   -lsnls11 -lnls11  -lcore11 -lsnls11 -lnls11 -lcore11 -lsnls11 -lnls11 -lxml11 -lcore11 -lunls11 -lsnls11 -lnls11 -lcore11 -lnls11 -lclient11 -lnnetd11  -lvsn11 -lcommon11 -lgeneric11 -lsnls11 -lnls11  -lcore11 -lsnls11 -lnls11 -lcore11 -lsnls11 -lnls11 -lxml11 -lcore11 -lunls11 -lsnls11 -lnls11 -lcore11 -lnls11   `cat /testdb/oracle/product/11204/lib/sysliblist` -Wl,-rpath,/testdb/oracle/product/11204/lib -lm    `cat /testdb/oracle/product/11204/lib/sysliblist` -ldl -lm   -L/testdb/oracle/product/11204/lib -lnl11  -ln11 -lnlsnr11 -lnlsnrc11 -lnsgr11 -lnms -lncm11 -lnmsp -lpeer -lnro11 -ln11   -lnl11 -lnlsnr11 -lnlsnrc11 -lnms -lncm11 -lnmsp -ln11     -lm
mv -f /testdb/oracle/product/11204/bin/lsnrctl /testdb/oracle/product/11204/bin/lsnrctl0
mv lsnrctl /testdb/oracle/product/11204/bin/lsnrctl
/bin/chmod 751 /testdb/oracle/product/11204/bin/lsnrctl

2. Restart Database Listener

$ lsnrctl start testdb

LSNRCTL for Linux: Version - Production on 16-MAY-2016 02:00:20

Copyright (c) 1991, 2013, Oracle.  All rights reserved.

Starting /testdb/oracle/product/11204/bin/tnslsnr: please wait...

TNSLSNR for Linux: Version - Production
System parameter file is /testdb/oracle/product/11204/network/admin/testdb/listener.ora
Log messages written to /testdb/log/network/testdb.log
Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=dblocalhost)(PORT=1523)))

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=dblocalhost)(PORT=1523)))
Alias                     testdb
Version                   TNSLSNR for Linux: Version - Production
Start Date                16-MAY-2016 02:00:20
Uptime                    0 days 0 hr. 0 min. 0 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Listener Parameter File   /testdb/oracle/product/11204/network/admin/testdb/listener.ora
Listener Log File         /testdb/log/network/testdb.log
Listening Endpoints Summary...
Services Summary...
Service "testdb" has 1 instance(s).
  Instance "testdb", status UNKNOWN, has 1 handler(s) for this service...
The command completed successfully

Thursday, 24 March 2016

Oracle RMAN Inremental Backup Algorithm and Change Tracking File

During an incremental backup, RMAN reads the SCN of each data block in the input file and compares it to the checkpoint SCN
of the parent incremental backup. If the SCN in the input data block is greater than or equal to the checkpoint SCN of the
parent, then RMAN copies the block.

Performance of incremental Backup can be improved by enabling block change tracking.When Change tracking is enabled, all the changes to datablocks are recored in change tracking file. RMAN can read the changed SCN's from change tracking file, instead of reading each and every input file.
One change tracking file is created for the entire database.
By default, the change tracking file is created as an Oracle managed file in DB_CREATE_FILE_DEST. We can specify the name of the block change tracking file by providing the location you choose.

SQL command to enable block change tracking

This creates change tracking file in "db_create_file_dest" directory

This creates the change tracking file in the location specified.

SQL command to disable block change tracking

By Default,  block change tracking is disabled.
If the change tracking feature is disabled, any existing change tracking files will be deleted

SQL query to find change tracking file Details

select filename, status from v$block_change_tracking

How to Relocate the change tracking file

1.Shut down the database


2.Using OS commands, move the change tracking file to a new location.

3.Mount the database and move the change tracking file to a location that has more space.

SQL query to rename change tracking file

ALTER DATABASE RENAME FILE   '/test1/data/rman_change_track.f' TO '/newtest1/data1/change_trk.f';

4.Open the database:


If we cannot afford downtime for database shutdown, change tracking file can be relocated as below


Contents of change tracking file will be lost if we use the above method.So its not a preferable method.
RMAN will have to scan the entire file until the next level 0 incremental backup is done

Advantages of RMAN Incremental Backups

What is RMAN Incremental Backup?

Incremental Backups take  back up  of only datafile blocks that have changed after a previous full backup. 
Incremental backups are applicable for databases, individual tablespaces or datafiles.

Benefits of RMAN Incremental Backup:

1.RMAN Incremental backups are used to periodically roll forward an image copy of the database

2.Reduced amount of time needed for Backups

3.Less Network bandwidth is required

4.To get adequate backup performance when the aggregate tape bandwidth available for tape write I/Os is much less than the aggregate disk bandwidth for disk read I/Os

5.To  recover changes to objects created with the NOLOGGING option. 

6.To reduce backup sizes for NOARCHIVELOG databases. Instead of making a whole database backup every time, you can make incremental backups.


If the database is in ARCHIVELOG mode,  incremental backups can be taken if the database is open;
If the database is in NOARCHIVELOG mode, then we can only make incremental backups after a consistent shutdown.

Click Here to know more about how incremental backup is implemented by RMAN and the imporatnace of block change tracking feature.