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Oracle Data Guard Interview Questions

Oracle Data Guard Interview Questions

Oracle Data Guard Interview Questions
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1)  How to setup Data Guard?

2) What are different types of modes in Data Guard and which is default?

ANS:

Maximum performance:
This is the default protection mode. 
It provides the highest level of data protection that is possible without affecting the performance of a primary database. 
This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log.

Maximum protection:
This protection mode ensures that no data loss will occur if the primary database fails. 
To provide this level of protection, the redo data needed to recover a transaction must be written to both the online redo log and to at least one standby database before the transaction commits. 
To ensure that data loss cannot occur, the primary database will shut down, rather than continue processing transactions.

Maximum availability:
This protection mode provides the highest level of data protection that is possible without compromising the availability of a primary database. 
Transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log and to at least one standby database.


3) How many standby databases we can create (in 10g/11g)?

ANS:

Till Oracle 10g, 9 standby databases are supported.
From Oracle 11g R2, we can create 30 standby databases..

4) What are the parameters we’ve to set in primary/standby for Data Guard ?

ANS:

DB_UNIQUE_NAME
LOG_ARCHIVE_CONFIG
LOG_ARCHIVE_MAX_PROCESSES
DB_CREATE_FILE_DEST
DB_FILE_NAME_CONVERT
LOG_FILE_NAME_CONVERT
LOG_ARCHIVE_DEST_n
LOGARCHIVE_DEST_STATE_n
FAL_SERVER
FAL_CLIENT
STANDBY_FILE_MANAGEMENT


5) What is the use of fal_server & fal_client, is it mandatory to set these ?


ANS:

FAL_SERVER
specifies the FAL (fetch archive log) server for a standby database. The value is an Oracle Net service name, which is assumed to be configured properly on the standby database system to point to the desired FAL server.


FAL_CLIENT
specifies the FAL (fetch archive log) client name that is used by the FAL service, configured through the
FAL_SERVER initialization parameter, to refer to the FAL client. 
The value is an Oracle Net service name, which is assumed to be configured properly on the FAL server system to point to the FAL client (standby database).


6) What are differences between physical, logical, snapshot standby and ADG (or) what are different types of standby databases?

Physical standby – in mount state, MRP will apply archives
ADG – in READ ONLY state, MRP will apply archives
Logical standby – in READ ONLY state, LSP will run
Snapshot standby databases – Physical standby database can be converted to snapshot standby database, which will be in READ WRITE mode, can do any kind of testing, then we can convert back snapshot standby database to physical standby database and start MRP which will apply all pending archives.

7) How to find out backlog of standby?

select round((sysdate - a.NEXT_TIME)*24*60) as "Backlog",m.SEQUENCE#-1 "Seq Applied",m.process, m.status 
from v$archived_log a, (select process,SEQUENCE#, status from v$managed_standby where process like '%MRP%')m where a.SEQUENCE#=(m.SEQUENCE#-1);

8) If you didn't have access to the standby database and you wanted to find out what error has occurred in a data guard configuration, what view would you check in the primary database to check the error message?

ANS:

You can check the v$dataguard_status view. 
select message from v$dataguard_status;


9) How can u recover standby which far behind from primary (or) without archive logs how can we make standby sync?

ANS:

By using RMAN incremental backup.


10) What is snapshot standby (or) How can we give a physical standby to user in READ WRITE mode and let him do updates and revert back to standby?

ANS:

Till Oralce 10g, create guaranteed restore point, open in read write, let him do updates, flashback to restore point, start MRP.

From Oracle 11g, convert physical standby to snapshot standby, let him do updates, convert to physical standby, start MRP.


11)  What are new features in 11g Data Guard?

ANS:

Here is some data guard category and there enhancement

1) Data Protection
Advanced Compression
Lost-write protection
Fast-Start Failover
2) Increase ROI
Active Data Guard
Snapshot Standby
3) High Availability
Faster Redo Apply
Faster failover & switchover
Automatic Failover using ASYNC
4) Manageability
Mixed Windows/Linux

12) What are the uses of standby redo log files


A standby redo log is required for the maximum protection and maximum availability modes and the LGWR ASYNC transport mode is recommended for all databases. Data Guard can recover and apply more redo data from a standby redo log than from archived redo log files alone.

If the real-time apply feature is enabled, log apply services can apply redo data as it is received, without waiting for the current standby redo log file to be archived. 
This results in faster switchover and failover times because the standby redo log files have been applied already to the standby database by the time the failover or switchover begins.

13) What is dg_config ?

ANS:

Specify the DG_CONFIG attribute to identify the DB_UNIQUE_NAME for the primary database and each standby database in the Data Guard configuration.
The default value of this parameter enables the primary database to send redo data to remote destinations and enables standby databases to receive redo data.

14) What is RTA (real time apply) mode MRP? 

ANS:

real-time apply where before log shipping the LGWR process writes to a standbylog file simultaneously along with the online redolog file. 
This standby logfile is written to standby log file on standby server. There is no loss of any committed transaction whatsoever in Real-Time Apply scenario.

•In Real Time Apply, once a transaction is committed on the Primary, the committed changes will be available on the Standby in Real Time even without switching the log at the Primary

MRP - Managed recovery process - For Data Guard, the background process that applies archived redo log to the standby database.

15)  What is the difference between normal MRP (managed apply) and RTA MRP (real time apply)?

ANS:


The difference between Redo Apply & Real-Time Apply
------------------------------------------------------
Normally, by default, Archiver processes will be responsible for Redo Transport from Primary to Standby.

Once a log switch happens on the Primary, the online redo log is archived in the Local Archive destination as pointed to by Log_archive_dest_1 
by an Archiver process. 
Another Archiver process will then transmit the redo to the remote standby destination as indicated by Log_archive_dest_2. 
Data Guard Remote File Server (RFS) Process on the Standby then writes redo data from the Standby redo log file to archive redo log file. 
Log apply services then makes use of Managed Recovery Process (MRP) process to apply the redo to the standby database.
This method of propagating redo from the primary to standby is called Redo Apply and it happens only on log switch at the Primary.
When using Redo Apply mode, the status of MRP in v$managed_standby view will show as WAIT_FOR_LOG.

Real Time Apply, in contrast, uses either LGWR or Archiver on the Primary to write redo data to Standby Redo log on the Standby and Log Apply Services can apply the redo data in real-time without the need of the current standby redo log being archived. Once a transaction is committed on the Primary, the committed changes will be available on the Standby in Real Time even without switching the log.

When using Real Time Apply mode, the status of MRP in v$managed_standby view will show as APPLYING_LOG.


16) What is the difference between SYNC/ASYNC, LGWR/ARCH, and AFFIRM/NOAFFIRM ?

ANS:

Specifies that network I/O is to be done synchronously (SYNC) or asynchronously (ASYNC) when archival is performed using the log writer process (LGWR).

Specifies whether redo transport services use archiver processes (ARCn) or the log writer process (LGWR) to collect transaction redo data and transmit it to standby destinations. If neither the ARCH or LGWR attributes are specified, the default is ARCH.

Controls whether redo transport services use synchronous or asynchronous I/O to write redo data to disk

AFFIRM—specifies that all disk I/O to archived redo log files and standby redo log files is performed synchronously and completes successfully before the log writer process continues.

NOAFFIRM—specifies that all disk I/O to archived redo log files and standby redo log files is performed asynchronously; the log writer process on the primary database does not wait until the disk I/O completes before continuing.


17) What is StaticConnectIdentifier property used for?

ANS:

11gr2 new database property, StaticConnectIdentifier, which allows the user to specify a static connect identifier that the DGMGRL client will use to start database instances.

18) What is failover/switchover (or) what is the difference between failover & switchover

ANS:

Switchover – This is done when both primary and standby databases are available. It is pre-planned.
Failover – This is done when the primary database is NO longer available (ie in a Disaster). It is not pre-planned.


29) What are the background processes involved in Data Guard?

ANS:

MRP, LSP, 

What is Dataguard?

Data Guard provides a comprehensive set of services that create, maintain, manage, and monitor one or more standby databases to enable production Oracle databases to survive disasters and data corruptions. Data Guard maintains these standby databases as copies of the production database. Data Guard can be used with traditional backup, restoration, and cluster techniques to provide a high level of data protection and data availability.

What is DG Broker?
DG Broker “it is the management and monitoring tool”.
Oracle dataguard broker is a distributed management framework that automates and centralizes the creation , maintenance and monitoring of DG configuration.
All management operations can be performed either through OEM, which uses the broker (or)  broker specified command-line tool interface “DGMGRL”.


What is the difference between Dataguard and Standby?

Dataguard  : 
Dataguard is mechanism/tool to maintain standby database.
The dataguard is set up between primary and standby instance .
Data Guard is only available on Enterprise Edition.

Standby Database :
Physical standby database provides a physically identical copy of the primary database, with on disk database structures that are identical to the primary database on a block-for-block basis.
Standby capability is available on Standard Edition. 

REFERENCE:
http://neeraj-dba.blogspot.in/2011/06/difference-between-dataguard-and.html

What are the differences between Physical/Logical standby databases? How would you decide which one is best suited for your environment?
Physical standby DB:
As the name, it is physically (datafiles, schema, other physical identity) same copy of the primary database.
It synchronized with the primary database with Apply Redo to the standby DB.
Logical Standby DB:
As the name logical information is the same as the production database, it may be physical structure can be different.
It synchronized with primary database though SQL Apply, Redo received from the primary database into SQL statements and then executing these SQL statements on the standby DB.
We can open “physical stand by DB to “read only” and make it available to the applications users (Only select is allowed during this period). we can not apply redo logs received from primary database at this time.
We do not see such issues with logical standby database. We can open the database in normal mode and make it available to the users. At the same time, we can apply archived logs received from primary database.

For OLTP large transaction database it is better to choose logical standby database.

Explain Active Dataguard?

11g  Active Data Guard
Oracle Active Data Guard enables read-only access to a physical standby database for queries, sorting, reporting, web-based access, etc., while continuously applying changes received from the production database.
Oracle Active Data Guard also enables the use of fast incremental backups when offloading backups to a standby database, and can provide additional benefits of high availability and disaster protection against planned or unplanned outages at the production site.

What is a Snapshot Standby Database?
11g Snapshot Standby Database
Oracle 11g introduces the Snapshot Standby database which essentially is an updateable standby database which has been created from a physical standby database.
We can convert a physical standby database to a snapshot standby database, do some kind of testing on a database which is a read write copy of the current primary or production database and then finally revert it to  it’s earlier state as a physical standby database.
While the snapshot standby database is open in read-write mode, redo is being received from the primary database, but is not applied.
After converting it back to a physical standby database, it is resynchronized with the primary by applying the accumalated redo data which was earlier shipped from the primary database but not applied.
Using a snapshot standby, we are able to do real time application testing using near real time production data. Very often we are required to do production clones for the purpose of testing. But using snapshot standby databases we can meet the same requirement sparing the effort,time,resources and disk space.

REFERENCE:
http://gavinsoorma.com/2009/07/11g-snapshot-standby-database/

Snapshot Standby Database (UPDATEABLE SNAPSHOT FOR TESTING)
A snapshot standby database is a fully updatable standby database that is created by converting a physical standby database into a snapshot standby database.

Like a physical or logical standby database, a snapshot standby database receives and archives redo data from a primary database. Unlike a physical or logical standby database, a snapshot standby database does not apply the redo data that it receives. The redo data received by a snapshot standby database is not applied until the snapshot standby is converted back into a physical standby database, after first discarding any local updates made to the snapshot standby database.

REFERENCE:
http://docs.oracle.com/cd/B28359_01/server.111/b28294/title.htm

What is the Default mode will the Standby will be, either SYNC or ASYNC?
ASYNC

Dataguard Architechture?
Data Guard Configurations:
A Data Guard configuration consists of one production database and one or more standby databases. The databases in a Data Guard configuration are connected by Oracle Net and may be dispersed geographically. There are no restrictions on where the databases are located, provided they can communicate with each other.

Dataguard Architecture
The Oracle 9i Data Guard architecture incorporates the following items: 

• Primary Database - A production database that is used to create standby databases. The archive logs from the primary database are transfered and applied to standby databases. Each standby can only be associated with a single primary database, but a single primary database can be associated with multiple standby databases.
• Standby Database - A replica of the primary database.
• Log Transport Services - Control the automatic transfer of archive redo log files from the primary database to one or more standby destinations.
• Network Configuration - The primary database is connected to one or more standby databases using      Oracle Net.
• Log Apply Services - Apply the archived redo logs to the standby database. The Managed Recovery      Process (MRP) actually does the work of maintaining and applying the archived redo logs.
• Role Management Services - Control the changing of database roles from primary to standby. The services include switchover, switchback and failover.
• Data Guard Broker - Controls the creation and monitoring of Data Guard. It comes with a GUI and command line interface.

Primary Database:
A Data Guard configuration contains one production database, also referred to as the primary database, that functions in the primary role. This is the database that is accessed by most of your applications.

Standby Database:
A standby database is a transactionally consistent copy of the primary database. Using a backup copy of the primary database, you can create up to nine standby databases and incorporate them in a Data Guard configuration. Once created, Data Guard automatically maintains each standby database by transmitting redo data from the primary database and then applying the redo to the standby database.
The types of standby databases are as follows:

Physical standby database:
Provides a physically identical copy of the primary database, with on disk database structures that are identical to the primary database on a block-for-block basis. The database schema, including indexes, are the same. A physical standby database is kept synchronized with the primary database, through Redo Apply, which recovers the redo data received from the primary database and applies the redo to the physical standby database.

Logical standby database:
Contains the same logical information as the production database, although the physical organization and structure of the data can be different. The logical standby database is kept synchronized with the primary database through SQL Apply, which transforms the data in the redo received from the primary database into SQL statements and then executes the SQL statements on the standby database. 

What are the services required on the primary and standby database ?
The services required on the primary database are:
• Log Writer Process (LGWR) - Collects redo information and updates the online redo logs. It can also      create local archived redo logs and transmit online redo to standby databases.
• Archiver Process (ARCn) - One or more archiver processes make copies of online redo logs either locally or remotely for standby databases.
• Fetch Archive Log (FAL) Server - Services requests for archive redo logs from FAL clients running on multiple standby databases. Multiple FAL servers can be run on a primary database, one for each FAL request. .
The services required on the standby database are:
• Fetch Archive Log (FAL) Client - Pulls archived redo log files from the primary site. Initiates transfer of archived redo logs when it detects a gap sequence.
• Remote File Server (RFS) - Receives archived and/or standby redo logs from the primary database.
• Archiver (ARCn) Processes - Archives the standby redo logs applied by the managed recovery process (MRP).
• Managed Recovery Process (MRP) - Applies archive redo log information to the standby database.

What is RTS (Redo Transport Services) in Dataguard?
It controls the automated transfer of redo data from the production database to one or more archival destinations. The redo transport services perform the following tasks:
a) Transmit redo data from the primary system to the standby systems in the configuration.
b) Manage the process of resolving any gaps in the archived redo log files due to a network failure.
c) Automatically detect missing or corrupted archived redo log files on a standby system and automatically retrieve replacement archived redo log files from the
primary database or another standby database. 

What are the Protection Modes in Dataguard?

Data Guard Protection Modes
This section describes the Data Guard protection modes.
In these descriptions, a synchronized standby database is meant to be one that meets the minimum requirements of the configured data protection mode and that does not have a redo gap. Redo gaps are discussed in Section 6.3.3.

Maximum Availability
This protectionmode provides the highest level of data protection that is possible without compromising the availability of a primary database. Transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log and to at least one synchronized standby database. If the primary database cannot write its redo stream to at least one synchronized standby database, it operates as if it were in maximum performance mode to preserve primary database availability until it is again able to write its redo stream to a synchronized standby database.
This mode ensures that no data loss will occur if the primary database fails, but only if a second fault does not prevent a complete set of redo data from being sent from the primary database to at least one standby database.

Maximum Performance
This protectionmode provides the highest level of data protection that is possible without affecting the performance of a primary database. This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log. Redo data is also written to one or more standby databases, but this is done asynchronously with respect to transaction commitment, so primary database performance is unaffected by delays in writing redo data to the standby database(s).
This protection mode offers slightly less data protection than maximum availability mode and has minimal impact on primary database performance.
This is the default protection mode.

Maximum Protection
This protection mode ensures that zero data loss occurs if a primary database fails. To provide this level of protection, the redo data needed to recover a transaction must be written to both the online redo log and to at least one synchronized standby database before the transaction commits. To ensure that data loss cannot occur, the primary database will shut down, rather than continue processing transactions, if it cannot write its redo stream to at least one synchronized standby database.
Because this data protection mode prioritizes data protection over primary database availability, Oracle recommends that a minimum of two standby databases be used to protect a primary database that runs in maximum protection mode to prevent a single standby database failure from causing the primary database to shut down.

How to delay the application of logs to a physical standby? 

A standby database automatically applies redo logs when they arrive from the primary database. But in some cases, we want to create a time lag between the archiving of a redo log at the primary site, and the application of the log at the standby site.

Modify the LOG_ARCHIVE_DEST_n initialization parameter on the primary database to set a delay for the standby database.

Example: For 60min Delay:
ALTER SYSTEM SET LOG_ARCHIVE_DEST_2='SERVICE=stdby_srvc DELAY=60';
The DELAY attribute is expressed in minutes.
The archived redo logs are still automatically copied from the primary site to the standby site, but the logs are not immediately applied to the standby database. The logs are applied when the specified time interval expires.

Steps to create Physical Standby database?

1.Take a full hot backup of Primary database
2.Create standby control file
3.Transfer full backup, init.ora, standby control file to standby node.
4.Modify init.ora file on standby node.
5.Restore database
6.Recover Standby database
(Alternatively, RMAN DUPLICATE DATABASE FOR STANDBY DO RECOVERY can be also used)
7.Setup FAL_CLIENT and FAL_SERVER parameters on both sides
8.Put Standby database in Managed Recover mode

What are the DATAGUARD PARAMETERS in Oracle?
Set Primary Database Initialization Parameters
----------------------------------------------
On the primary database, you define initialization parameters that control redo transport services while the database is in the primary role. There are additional parameters you need to add that control the receipt of the redo data and log apply services when the primary database is transitioned to the standby role.

DB_NAME=chicago
DB_UNIQUE_NAME=chicago
LOG_ARCHIVE_CONFIG='DG_CONFIG=(chicago,boston)'
CONTROL_FILES='/arch1/chicago/control1.ctl', '/arch2/chicago/control2.ctl'
LOG_ARCHIVE_DEST_1=
 'LOCATION=/arch1/chicago/
  VALID_FOR=(ALL_LOGFILES,ALL_ROLES)
  DB_UNIQUE_NAME=chicago'
LOG_ARCHIVE_DEST_2=
 'SERVICE=boston LGWR ASYNC
  VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE)
  DB_UNIQUE_NAME=boston'
LOG_ARCHIVE_DEST_STATE_1=ENABLE
LOG_ARCHIVE_DEST_STATE_2=ENABLE
REMOTE_LOGIN_PASSWORDFILE=EXCLUSIVE
LOG_ARCHIVE_FORMAT=%t_%s_%r.arc
LOG_ARCHIVE_MAX_PROCESSES=30

Primary Database: Standby Role Initialization Parameters
FAL_SERVER=boston
FAL_CLIENT=chicago
DB_FILE_NAME_CONVERT='boston','chicago'
LOG_FILE_NAME_CONVERT=  '/arch1/boston/','/arch1/chicago/','/arch2/boston/','/arch2/chicago/'
STANDBY_FILE_MANAGEMENT=AUTO

Prepare an Initialization Parameter File for the Standby Database
-----------------------------------------------------------------
Create a text initialization parameter file (PFILE) from the server parameter file (SPFILE) used by the primary database; a text initialization parameter file can be copied to the standby location and modified. For example:
CREATE PFILE='/tmp/initboston.ora' FROM SPFILE;

Modifying Initialization Parameters for a Physical Standby Database.

DB_NAME=chicago
DB_UNIQUE_NAME=boston
LOG_ARCHIVE_CONFIG='DG_CONFIG=(chicago,boston)'
CONTROL_FILES='/arch1/boston/control1.ctl', '/arch2/boston/control2.ctl'
DB_FILE_NAME_CONVERT='chicago','boston'
LOG_FILE_NAME_CONVERT= '/arch1/chicago/','/arch1/boston/','/arch2/chicago/','/arch2/boston/'
LOG_ARCHIVE_FORMAT=log%t_%s_%r.arc
LOG_ARCHIVE_DEST_1=  'LOCATION=/arch1/boston/
VALID_FOR=(ALL_LOGFILES,ALL_ROLES) 
DB_UNIQUE_NAME=boston'
LOG_ARCHIVE_DEST_2=  'SERVICE=chicago LGWR ASYNC  VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE)   DB_UNIQUE_NAME=chicago'
LOG_ARCHIVE_DEST_STATE_1=ENABLE
LOG_ARCHIVE_DEST_STATE_2=ENABLE
REMOTE_LOGIN_PASSWORDFILE=EXCLUSIVE
STANDBY_FILE_MANAGEMENT=AUTO
FAL_SERVER=chicago
FAL_CLIENT=boston

http://sarith.wordpress.com/tag/oracle-10g-data-guard/


Primary DB Dataguard Parameter?

Parameters responsible for Failover in Dataguard?

Difference between FAL_SERVER (Fetch Archive Log) Vs. FAL_Client

What is RFS?

If DR has different file location, which parameter need to be chamged?

Can we have Standby Database in STANDARD EDITION?

Can we have Primary Database in SOLARIS OS and Standby in LINUX OS?

What are DR creation Prerequisites?
Dataguard creation steps?

Why password file in dataguard? 

Oracle RAC Interview Questions

1) What is the use of RAC

ANS:

Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously while accessing a single database, thus providing clustering.

2) What are the prerequisites for RAC setup ?


3) What are Oracle Clusterware/Daemon processes and what they do?

Ans:
ocssd, crsd, evmd, oprocd, racgmain, racgimon

4) What are the special background processes for RAC (or) what is difference in stand-alone database & RAC database background processes?

ANS:

DIAG, LCKn, LMD, LMSn, LMON 

5) What are structural changes in 11g R2 RAC?

Ans:
http://satya-racdba.blogspot.com/2010/07/new-features-in-9i-10g-11g-rac.html
Grid & ASM are on one home, 
Voting disk & ocrfile can be on the ASM,
SCAN,
By using srvctl, we can mange diskgroups, home, ons, eons, filesystem, srvpool, server, scan, scan_listener, gns, vip, oc4j,GSD

6) What is cache fusion?

Ans:
Transferring of data between RAC instances by using private network. 
Cache Fusion is the remote memory mapping of Oracle buffers, 
shared between the caches of participating nodes in the cluster.
When a block of data is read from datafile by an instance within the cluster and another instance is in need of the same block, 
it is easy to get the block image from the instance which has the block in its SGA rather than reading from the disk.



7) What is the purpose of Private Interconnect?

Ans:

Clusterware uses the private interconnect for cluster synchronization (network heartbeat) and daemon communication between the clustered nodes. This communication is based on the TCP protocol. 
RAC uses the interconnect for cache fusion (UDP) and inter-process communication (TCP).



8) What are the Clusterware components?

Ans:

Voting Disk - Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of network failures. The voting disk must reside on shared disk.

Oracle Cluster Registry (OCR) - Maintains cluster configuration information as well as configuration information about any cluster database within the cluster. The OCR must reside on shared disk that is accessible by all of the nodes in your cluster. 
The daemon OCSSd manages the configuration info in OCR and maintains the changes to cluster in the registry.

Virtual IP (VIP) - When a node fails, the VIP associated with it is automatically failed over to some other node 
and new node re-arps the world indicating a new MAC address for the IP. 
Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. 
This results in the clients getting errors immediately.
crsd – Cluster Resource Services Daemon
cssd – Cluster Synchronization Services Daemon
evmd – Event Manager Daemon
oprocd / hangcheck_timer – Node hang detector



9) What is OCR file?

Ans:
RAC configuration information repository that manages information about the cluster node list and instance-to-node mapping information. 
The OCR also manages information about Oracle Clusterware resource profiles for customized applications.
Maintains cluster configuration information as well as configuration information about any cluster database within the cluster. 
The OCR must reside on shared disk that is accessible by all of the nodes in your cluster. 
The daemon OCSSd manages the configuration info in OCR and maintains the changes to cluster in the registry.


10) What is Voting file/disk and how many files should be there?

Ans:
Voting Disk File is a file on the shared cluster system or a shared raw device file. 
Oracle Clusterware uses the voting disk to determine which instances are members of a cluster. 
Voting disk is akin to the quorum disk, which helps to avoid the split-brain syndrome. 
Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances 
in case of network failures. The voting disk must reside on shared disk.

11) How to take backup of OCR file?

Ans:
#ocrconfig -manualbackup
#ocrconfig -export file_name.dmp
#ocrdump -backupfile my_file
$cp -p -R /u01/app/crs/cdata /u02/crs_backup/ocrbackup/RAC1


12) How to recover OCR file?

Ans:
#ocrconfig -restore backup_file.ocr
#ocrconfig -import file_name.dmp


13) What is local OCR?

Ans:
/etc/oracle/local.ocr
/var/opt/oracle/local.ocr


14) How to check backup of OCR files?

Ans:
#ocrconfig –showbackup


15) How to take backup of voting file?

Ans:
dd if=/u02/ocfs2/vote/VDFile_0 of=$ORACLE_BASE/bkp/vd/VDFile_0
crsctl backup css votedisk         -- from 11g R2

16)  How do I identify the voting disk location?

Ans:
# crsctl query css votedisk

17) How do I identify the OCR file location?

check /var/opt/oracle/ocr.loc or /etc/ocr.loc

Ans:
# ocrcheck


18) If voting disk/OCR file got corrupted and don’t have backups, how to get them?

Ans:
We have to install Clusterware.


19) Who will manage OCR files?

Ans:
cssd will manage OCR.



20)  Who will take backup of OCR files?

Ans:
crsd will take backup.


21) What is split brain syndrome?

Ans:
Will arise when two or more instances attempt to control a cluster database. 
In a two-node environment, one instance attempts to manage updates simultaneously while the other instance attempts to manage updates.


22) What are various IPs used in RAC? Or How may IPs we need in RAC?

Ans:
Public IP, Private IP, Virtual IP, SCAN IP


23) What is the use of virtual IP?

Ans:
When a node fails, 
the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC address for the IP. 
Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. 
This results in the clients getting errors immediately.

Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error. 
As a result, you don't really have a good HA solution without using VIPs.

24) What is the use of SCAN IP (SCAN name) and will it provide load balancing?

Ans:
Single Client Access Name (SCAN) is a new Oracle Real Application Clusters (RAC) 11g Release 2, 
feature that provides a single name for clients to access an Oracle Database running in a cluster. 
The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.

25)  How many SCAN listeners will be running?

Ans:
Three SCAN listeners only.

26) What is FAN?

Ans:
Applications can use Fast Application Notification (FAN) to enable rapid failure detection, balancing of connection pools after failures, 
and re-balancing of connection pools when failed components are repaired. 
The FAN process uses system events that Oracle publishes when cluster servers become unreachable or if network interfaces fail.


27) What is FCF?

Ans:
Fast Connection Failover provides high availability to FAN integrated clients, such as clients that use JDBC, OCI, or ODP.NET. 
If you configure the client to use fast connection failover, then the client automatically subscribes to FAN events and can react to database UP and DOWN events. 
In response, Oracle gives the client a connection to an active instance that provides the requested database service.


30) What is TAF and TAF policies?

Ans:
Transparent Application Failover (TAF) - A runtime failover for high availability environments, 
such as Real Application Clusters and Oracle Real Application Clusters Guard, TAF refers to the failover and re-establishment of application-to-service connections. 
It enables client applications to automatically reconnect to the database if the connection fails, and optionally resume a SELECT statement that was in progress. 
This reconnect happens automatically from within the Oracle Call Interface (OCI) library.

31) What are nodeapps?

Ans:
VIP, listener, ONS, GSD


32) What is gsd (Global Service Daemon)?   [ http://www.datadisk.co.uk/html_docs/rac/rac_cs.htm ]

runs on each node with one GSD process per node. 
The GSD coordinates with the cluster manager to receive requests from clients such as the DBCA, EM, and the SRVCTL utility to execute administrative job tasks such as instance startup or shutdown. 
The GSD is not an Oracle instance background process and is therefore not started with the Oracle instance

33) How to do load balancing in RAC?


Client Side Connect-Time Load Balance:
---------------------------------------
The client load balancing feature enables clients to randomize connection requests among the listeners. 
This is done by client Tnsnames Parameter: LOAD_BALANCE.
The (load_balance=yes) instructs SQLNet to progress through the list of listener addresses in the address_list section of the net service name in a random sequence. When set to OFF, instructs SQLNet to try the addresses sequentially until one succeeds. 

Client Side Connect-Time failover 
-------------------------------------
This is done by client Tnsnames Parameter: FAILOVER
The (failover=on) enables clients to connect to another listener if the initial connection to the first listener fails. Without connect-time failover, Oracle Net attempts a connection with only one listener. 

Server Side Listener Connection Load Balancing.
-------------------------------------------------
With server-side load balancing, the listener directs a connection request to the best instance currently providing the service.
Init parameter remote_listener should be set. When set, each instance registers with the TNS listeners running on all nodes within the cluster. 

There are two types of server-side load balancing: 
--------------------------------------------------
Load Based — Server side load balancing redirects connections by default depending on node load. This id default.
Session Based — Session based load balancing takes into account the number of sessions connected to each node and then distributes the connections to balance the number of sessions across the different nodes.

From 10g release 2 the service can be setup to use load balancing advisory. This mean connections can be routed using SERVICE TIME and THROUGHPUT. Connection load balancing means the goal of a service can be changed, to reflect the type of connections using the service. 

Transparent Application Failover (TAF) :
----------------------------------------------
Transparent Application Failover (TAF) is a feature of the Oracle Call Interface (OCI) driver at client side. It enables the application to automatically reconnect to a database, if the database instance to which the connection is made fails. In this case, the active transactions roll back. 
Tnsnames Parameter: FAILOVER_MODE

e.g (failover_mode=(type=select)(method=basic)) 
Failover Mode Type can be Either SESSION or SELECT.

Session failover will have just the session to failed over to the next available node. With SELECT, the select query will be resumed.
TAF can be configured with just server side service settings by using dbms_service package.

Fast Connection Failover (FCF):
-----------------------------------
Fast Connection Failover is a feature of Oracle clients that have integrated with FAN HA Events.
Oracle JDBC Implicit Connection Cache, Oracle Call Interface (OCI), and Oracle Data Provider for .Net (ODP.Net) include fast connection failover. 

With fast connection failover, when a down event is received, cached connections affected by the down event are immediately marked invalid and cleaned up.



34) What are the uses of services? How to find out the services in cluster?

Ans:
Applications should use the services to connect to the Oracle database. 
Services define rules and characteristics (unique name, workload balancing, failover options, and high availability) to control how users and applications connect to database instances.

35) How to find out the nodes in cluster (or) how to find out the master node?

Ans:

# olsnodes  -- Which ever displayed first, is the master node of the cluster.

select MASTER_NODE from v$ges_resource;

To find out which is the master node, you can see ocssd.log file and search for "master node number".


36) How to know the public IPs, private IPs, VIPs in RAC?

Ans:
# olsnodes -n -p -i
node1-pub       1       node1-prv       node1-vip
node2-pub       2       node2-prv       node2-vip


37) What utility is used to start DB/instance?

Ans:
srvctl start database –d database_name
srvctl start instance –d database_name –i instance_name


38) How can you shutdown single instance?

Ans:
Change cluster_database=false

srvctl stop instance –d database_name –i instance_name

39) What is HAS (High Availability Service) and the commands?

Ans:
HAS includes ASM & database instance and listeners.

crsctl check has
crsctl config has
crsctl disable has
crsctl enable has
crsctl query has releaseversion
crsctl query has softwareversion
crsctl start has
crsctl stop has [-f]


40) How many nodes are supported in a RAC Database?

Ans:
10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.



41) What is fencing?

Ans:
I/O fencing prevents updates by failed instances, and detecting failure and preventing split brain in cluster. 
When a cluster node fails, the failed node needs to be fenced off from all the shared disk devices or diskgroups. 
This methodology is called I/O Fencing, sometimes called Disk Fencing or failure fencing.


42) Why Clusterware installed in root (why not oracle)?

Oracle Clusterware works closely with the operating system, system administrator access is required for some of the installation tasks. 
In addition, some of the Oracle Clusterware processes must run as the special operating system user, root.


43) What are the wait events in RAC?

Ans:
http://satya-racdba.blogspot.com/2012/10/wait-events-in-oracle-rac-wait-events.html

http://orainternals.wordpress.com/2009/12/23/rac-performance-tuning-understanding-global-cache-performance/

gc buffer busy
gc buffer busy acquire
gc current request 
gc cr request
gc cr failure 
gc current block lost
gc cr block lost
gc current block corrupt
gc cr block corrupt
gc current block busy
gc cr block busy
gc current block congested
gc cr block congested.
gc current block 2-way
gc cr block 2-way
gc current block 3-way
gc cr block 3-way
(gc current/cr block n-way, n is number of nodes)
gc current grant 2-way
gc cr grant 2-way
gc current grant busy
gc current grant congested
gc cr grant congested
gc cr multi block read
gc current multi block request
gc cr multi block request
gc cr block build time
gc current block flush time
gc cr block flush time
gc current block send time
gc cr block send time
gc current block pin time
gc domain validation 
gc current retry
ges inquiry response
gcs log flush sync


44) What are the initialization parameters that must have same value for every instance in an Oracle RAC database?
Ans:
http://satya-racdba.blogspot.com/2012/09/init-parameters-in-oracle-rac.html

ACTIVE_INSTANCE_COUNT
ARCHIVE_LAG_TARGET
COMPATIBLE
CLUSTER_DATABASE
CLUSTER_DATABASE_INSTANCE
CONTROL_FILES
DB_BLOCK_SIZE
DB_DOMAIN
DB_FILES
DB_NAME
DB_RECOVERY_FILE_DEST
DB_RECOVERY_FILE_DEST_SIZE
DB_UNIQUE_NAME
INSTANCE_TYPE
PARALLEL_MAX_SERVERS
REMOTE_LOGIN_PASSWORD_FILE
UNDO_MANAGEMENT


45) What is the difference between cr block and cur (current) block?



46) New features in Oracle Clusterware 12c ?


Oracle Flex ASM - This feature of Oracle Clusterware 12c claims to reduce per-node overhead of using ASM instance. 
Now the instances can use remote node ASM for any planned/unplanned downtime. ASM metadata requests can be converted by non-local instance of ASM.

ASM Disk Scrubbing - From RAC 12c, ASM comes with disk scrubbing feature so that logical corruptions can be discovered. 
Also Oracle 12c ASM can automatically correct this in normal or high redundancy diskgroups.

Oracle ASM Disk Resync & Rebalance enhancements.
Commands Databases Supporting To the application Gameing Game What is raid

Application Continuity (AC) - is transparent to the application and in-case the database or the infrastructure is unavailable, this new features which work on JDBC drivers, masks recoverable outages. 
This recovers database session beneath the application so that the outage actually appears to be delayed connectivity or execution. 
Transaction guard (improvements of Fast Application Notification).

IPv6 Support - Oracle RAC 12c now supports IPv6 for Client connectivity, Interconnect is still on IPv4.

Per Subnet multiple SCAN - RAC 12c, per-Subnet multiple SCAN can be configured per cluster.

Each RAC instance opens the Container Database (CDB) as a whole so that versions would be same for CDB as well as for all of the Pluggable Databases (PDBs). PDBs are also fully compatible with RAC.

Oracle installer will run root.sh script across nodes. We don't have to run the scripts manually on all RAC nodes. 

new "ghctl" command for patching.



47) New features in Oracle 9i/10g/11g RAC ?  [ http://satya-racdba.blogspot.in/2010/07/new-features-in-9i-10g-11g-rac.html ]


Oracle Real Application Clusters New features

Oracle 9i RAC:
---------------------
OPS (Oracle Parallel Server) was renamed as RAC
CFS (Cluster File System) was supported
OCFS (Oracle Cluster File System) for Linux and Windows
watchdog timer replaced by hangcheck timer

Oracle 10g R1 RAC :
-------------------
Cluster Manager replaced by CRS
ASM introduced
Concept of Services expanded
ocrcheck introduced
ocrdump introduced
AWR was instance specific

Oracle 10g R2 RAC :
-------------------
CRS was renamed as Clusterware
asmcmd introduced
CLUVFY introduced
OCR and Voting disks can be mirrored
Can use FAN/FCF with TAF for OCI and ODP.NET
The Waiting The Wait Latest News Resource Manager Installing Music Downloads


Oracle 11g R1 RAC :
---------------------
--> Oracle 11g RAC parallel upgrades - Oracle 11g have rolling upgrade features whereby RAC database can be upgraded without any downtime.
-->Hot patching - Zero downtime patch application.
-->Oracle RAC load balancing advisor - Starting from 10g R2 we have RAC load balancing advisor utility. 
11g RAC load balancing advisor is only available with clients who use .NET, ODBC, or the Oracle Call Interface (OCI).
-->ADDM for RAC - Oracle has incorporated RAC into the automatic database diagnostic monitor, for cross-node advisories. 
The script addmrpt.sql run give report for single instance, will not report all instances in RAC, this is known as instance ADDM. 
But using the new package DBMS_ADDM, we can generate report for all instances of RAC, this known as database ADDM.
--> Optimized RAC cache fusion protocols - moves on from the general cache fusion protocols in 10g to deal with specific scenarios where the protocols could be further optimized.
--> Oracle 11g RAC Grid provisioning - The Oracle grid control provisioning pack allows us to "blow-out" a RAC node without the time-consuming install, using a pre-installed "footprint".

Oracle 11g R2 RAC :
-----------------------
--> We can store everything on the ASM. We can store OCR & voting files also on the ASM.
--> ASMCA
--> Single Client Access Name (SCAN) - eliminates the need to change tns entry when nodes are added to or removed from the Cluster. 
RAC instances register to SCAN listeners as remote listeners. SCAN is fully qualified name.
Oracle recommends assigning 3 addresses to SCAN, which create three SCAN listeners.
--> Clusterware components: crfmond, crflogd, GIPCD.
--> AWR is consolidated for the database.
--> 11g Release 2 Real Application Cluster (RAC) has server pooling technologies so it’s easier to provision and manage database grids. 
This update is geared toward dynamically adjusting servers as corporations manage the ebb and flow between data requirements for datawarehousing and applications.By default, LOAD_BALANCE is ON.
--> GSD (Global Service Deamon), gsdctl introduced.
--> GPnP profile.
--> Cluster information in an XML profile.
--> Oracle RAC OneNode is a new option that makes it easier to consolidate databases that aren’t mission critical, but need redundancy.
--> raconeinit - to convert database to RacOneNode.
--> raconefix - to fix RacOneNode database in case of failure.
--> racone2rac - to convert RacOneNode back to RAC.
--> Oracle Restart - the feature of Oracle Grid Infrastructure's High Availability Services (HAS) to manage associated listeners, ASM instances and Oracle instances.
--> Oracle Omotion - Oracle 11g release2 RAC introduces new feature called Oracle Omotion, an online migration utility. 
This Omotion utility will relocate the instance from one node to another, whenever instance failure happens.
Omotion utility uses Database Area Network (DAN) to move Oracle instances. 
Database Area Network (DAN) technology helps seamless database relocation without losing transactions.
--> Cluster Time Synchronization Service (CTSS) is a new feature in Oracle 11g R2 RAC, which is used to synchronize time across the nodes of the cluster. --> CTSS will be replacement of NTP protocol.
--> Grid Naming Service (GNS) is a new service introduced in Oracle RAC 11g R2. With GNS, Oracle Clusterware (CRS) can manage Dynamic Host Configuration Protocol --> (DHCP) and DNS services for the dynamic node registration and configuration.
--> Cluster interconnect: Used for data blocks, locks, messages, and SCN numbers.
--> Oracle Local Registry (OLR) - From Oracle 11gR2 "Oracle Local Registry (OLR)" something new as part of Oracle Clusterware. OLR is node’s local repository, --> similar to OCR (but local) and is managed by OHASD. It pertains data of local node only and is not shared among other nodes.
--> Multicasting is introduced in 11gR2 for private interconnect traffic.
--> I/O fencing prevents updates by failed instances, and detecting failure and preventing split brain in cluster. When a cluster node fails, the failed node needs to be fenced off from all the shared disk devices or diskgroups. This methodology is called I/O Fencing, sometimes called Disk Fencing or failure fencing.
--> Re-bootless node fencing (restart)? - instead of fast re-booting the node, a graceful shutdown of the stack is attempted.
--> Clusterware log directories: acfs*
--> HAIP (IC VIP).
--> Redundant interconnects: NIC bonding, HAIP.
--> RAC background processes: DBRM – Database Resource Manager, PING – Response time agent.
--> Virtual Oracle 11g RAC cluster - Oracle 11g RAC supports virtualization.