Friday, 5 May 2017

Oracle Database Administrator Interview Questions on RMAN


1.What is the difference between recovery catalog and Nocatalog backup in RMAN?

NoCatalog Backup:

ByDefault RMAN connects to the target database in Nocatalog Mode.
In Nocatalog Mode, Backup Information and Metadata related to RMAN is stored in target database controlfile.

Catalog Backup:

A recovery catalog is a schema created in a separate database that contains metadata obtained from the target control file.
In recovery catalog we can store rman scripts.

We can store metadata about multiple incarnations of a single target database in the catalog.
Recovery catalog is central and can have information of many databases.
If the control file is lost and must be restored from backup, the backup configuration information is available when the database is not mounted.

2.What are the differences between crosscheck and validate commands?

Validate command is to examine a backup set and report whether it can be restored. RMAN scans all of the backup pieces in the specified backup sets and looks at the checksum to verify that the contents are intact so that backup can be successfully restored if necessary.

Crosscheck command is to verify the status of backups and copies recorded in the RMAN repository against media such as disk or tape. The crosscheck command only processes files created on the same device type as the channel running crosscheck.

3.What is obsolete backup & expired backup?

A status of “expired” means that the backup piece or backup set is not found in the backup destination.

A status of “obsolete” means the backup piece is still available, but it is no longer needed. The backup piece is no longer needed since RMAN has been configured to no longer need this piece after so many days have elapsed, or so many backups have been performed.

4.What is the difference between hot backup & RMAN backup?

We need to put the database in Backup mode for Hot  Backup. RMAN Backup does not need the database to be in Backup mode.

5. Which Tables are have information required for RMAN list & report commands ?
 V$BACKUP_FILES and recovery catalog views e.g.,  RC_DATAFILE_COPY or RC_ARCHIVED_LOG.

Below tables contain RMAN Catalog information:


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

Weblogic Managed Servers Crashed due to weblogic.socket.MaxMessageSizeExceededException


Weblogic Managed Servers are crashing frequently .

Admin Server Logfile has the below error message.

 <IOException occurred on socket: Socket[,port=1345,localport=47093]
weblogic.socket.MaxMessageSizeExceededException: Incoming message of size: '10000080' bytes exceeds the configured maximum of: '10000000' bytes for protocol: 't3'.
weblogic.socket.MaxMessageSizeExceededException: Incoming message of size: '10000080' bytes exceeds the configured maximum of: '10000000' bytes for protocol: 't3'
at weblogic.socket.BaseAbstractMuxableSocket.incrementBufferOffset(
at weblogic.rjvm.t3.MuxableSocketT3.incrementBufferOffset(
at weblogic.socket.SocketMuxer.readFromSocket(
at weblogic.socket.SocketMuxer.readReadySocketOnce(
at weblogic.socket.SocketMuxer.readReadySocket(
at weblogic.socket.EPollSocketMuxer.dataReceived(
at weblogic.socket.EPollSocketMuxer.processSockets(
at weblogic.socket.SocketReaderRequest.execute(
at weblogic.kernel.ExecuteThread.execute(

Due to above error, Admin Server is going into WARNING Status and Managed Servers are disconnected from ADMIN Server.


1. Increase Maxmessage size from WLS console

Login to weblogic console url as weblogic admin user

WebLogic Console -> Servers ->Admin Server ->  Protocols -> General -> Max Message 

Increase Max Message Size to  20000000 (Any value higher than Incoming message size from error message)

2.Restart MT Services