Data Guard Configuration
A Data Guard configuration consists of one production (or primary) database and up to nine 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 that they can communicate with each other.
Redo Apply and SQL Apply
A standby database is initially created from a backup copy of the primary database. Once created, Data Guard automatically maintains the standby database as a synchronized copy of the primary database by transmitting primary database redo data to the standby system and then applying the redo data to the standby database.
Data Guard provides two methods to apply this redo data to the standby database and keep it synchronized with the primary, and these methods correspond to the two types of standby databases supported by Data Guard.
* Redo Apply, used for physical standby databases
* SQL Apply, used for logical standby databases
A 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. The Redo Apply technology applies redo data on the physical standby database using standard Oracle media recovery techniques. In addition to traditional Data Guard functionality, the Active Data Guard Option for Oracle Database 11g enables a physical standby database to be open read-only while it applies updates received from the primary database. This makes physical standby databases useful for offloading the primary database from the overhead of processing read-only queries and reports. This also makes it simple to validate that the standby database is synchronized with the primary database at all times.
A 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 SQL apply technology keeps the logical standby database synchronized with the primary database by transforming redo data received from the primary database into SQL statements and then executing the SQL statements on the standby database. This makes it possible for the logical standby database to be open read-write and accessed for queries and reporting purposes at the same time the SQL is being applied to it.
Role Management
Using Data Guard, the role of a database can be switched from a primary role to a standby role and vice versa, ensuring no data loss in the process, and minimizing downtime. There are two kinds of role transitions - a switchover and a failover. A switchover is a role reversal between the primary database and one of its standby databases. This is typically done for planned maintenance of the primary system. During a switchover, the primary database transitions to a standby role and the standby database transitions to the primary role. The transition occurs without having to re-create either database. A failover is a transition of a standby database to the primary role following a sudden outage of the primary database. The failed primary can be reinstated as a standby database for the new primary using Oracle Flashback Database. This can eliminate the need to recreate the failed primary from a backup, dramatically reducing the time and effort required to return the configuration to a protected state. Administrators have the option of executing failovers manually, or Data Guard can be configured to automatically detect primary database failures and execute a failover to the standby database without manual intervention.
Data Guard Protection Modes
In some situations, a business cannot afford to lose data at any cost. In other situations, some applications require maximum database performance and can tolerate a potential loss of data. Data Guard provides three distinct modes of data protection to satisfy these varied requirements:
*
Maximum Protection—This mode offers the highest level of data protection. Data is synchronously transmitted to the standby database from the primary database and transactions are not committed on the primary database unless the redo data is available on at least one standby database configured in this mode. If the last standby database configured in this mode becomes unavailable, processing stops on the primary database. This mode ensures no-data-loss, even in the event of multiple failures.
*
Maximum Availability—This mode is similar to the maximum protection mode, including zero data loss. However, if a standby database becomes unavailable (for example, because of network connectivity problems), processing continues on the primary database. When the fault is corrected, the standby database is automatically resynchronized with the primary database. This mode achieves no-data-loss in the event of a single failure (e.g. network failure, primary site failure . . .)
*
Maximum Performance—This mode offers slightly less data protection on the primary database, but higher performance than maximum availability mode. In this mode, as the primary database processes transactions, redo data is asynchronously shipped to the standby database. The commit operation of the primary database does not wait for the standby database to acknowledge receipt of redo data before completing write operations on the primary database. If any standby destination becomes unavailable, processing continues on the primary database and there is little effect on primary database performance.
Data Guard Broker
The Oracle Data Guard Broker is a distributed management framework that automates and centralizes the creation, maintenance, and monitoring of Data Guard configurations. All management operations can be performed either through Oracle Enterprise Manager, which uses the Broker, or through the Broker's specialized command-line interface (DGMGRL). Data Guard Broker 11g also enables automatic database failover for Data Guard configurations using either Maximum Availability or Maximum Performance modes.
Oracle 10 DBA Interview questions and answers
1. Is the following SQL statement syntactically correct? If not, please rewrite it correctly.
SELECT col1 FROM tableA WHERE NOT IN (SELECT col1 FROM tableB);
Ans. SQL is incorrect.
Correct SQL : SELECT col1 FROM tableA WHERE col1 NOT IN (SELECT col1 FROM tableB);
2. What is a more efficient way to write this query, to archive the same set?
Ans: SELECT col1 from tableA minus SELECT col1 from tableB
3.How would you determine that the new query is more efficient than the original query?
Ans: Run explain plan on both query and see the result .
4.How can we find the location of the database trace files from within the data dictionary?
Ans: Generally trace file on the database server machine is located in one of two locations:
1. If you are using a dedicated server connection, the trace file will be generated in the directory specified by
the USER_DUMP_DEST parameter.
2.If you are using a shared server connection, the trace file will be generated in the directory specified by the
BACKGROUND_DUMP_DEST parameter.
you can run sqlplus>SHOW PARAMETER DUMP_DEST
or
select name, value
from v$parameter
where name like '%dump_dest%'
5. What is the correct syntax for a UNIX endless WHILE loop?
while :
do
commands
done
6. Write the SQL statement that will return the name and size of the largest datafile in the database.
SQL> select name,bytes from v$datafile where bytes=(select max(bytes) from v$datafile);
7. What are the proper steps to changing the Oracle database block size?
cold backup all data files and backup controlfile to trace, recreate your database
with the new block size using the backup control file, and restore. It may be easier
with rman. You can not change datbase block size on fly.
8. Using awk, write a script to print the 3rd field of every line.
Ans:
awk '{print }'
awk '{print $3}
awk '{print $3}
9.Under what conditions, is a nested loop better than a merge join?
Ans:
Optimizer uses nested loop when we are joining tables containing small number of rows with an efficient driving
condition.
It is important to have an index on column of inner join table as this table is probed every time for a new value
from outer table.
Optimizer may not use nested loop in case:
1. No of rows of both the table is quite high
2. Inner query always results in same set of records
3. The access path of inner table is independent of data coming from outer table.
merge join is used to join two independent data sources. They perform better than nested loop when the volume of
data is big in tables
but not as good as hash joins in general.
10.Which database views would you use to ascertain the number of commits a user's session has performed?
Joining V$SESSTAT ,V$STATNAME
select * from V$SESSTAT a ,V$STATNAME b where b.CLASS=a.STATISTIC# and b.NAME='user commits' and a.sid=
11.What does the #!bin/ksh at the beginning of a shell script do? Why should it be there?
Ans: On the first line of an interpreter script, the "#!", is the name of a program which should be used to
interpret the contents of the file.
For instance, if the first line contains "#! /bin/ksh", then the contents of the file are executed as a korn shell
script.
12.What command is used to find the status of Oracle 10g Clusterware (CRS) and the various components it manages
(ONS, VIP, listener, instances, etc.)?
Ans:
$ocrcheck
13.Describe a scenario in which a vendor clusterware is required, in addition to the Oracle 10g Clusterware.
If you choose external redundancy for the OCR and voting disk, then to enable redundancy, the disk subsystem must be configurable for RAID mirroring/vendor clusterware. Otherwise, your system may be vulnerable because the OCR and voting disk are single points of failure.
14.How would you find the interconnect IP address from any node within an Oracle 10g RAC configuration?
using oifcfg command.
se the oifcfg -help command to display online help for OIFCFG. The elements of OIFCFG commands, some of which are
optional depending on the command, are:
*nodename—Name of the Oracle Clusterware node as listed in the output from the olsnodes command
*if_name—Name by which the interface is configured in the system
*subnet—Subnet address of the interface
*if_type—Type of interface: public or cluster_interconnect
You can use OIFCFG to list the interface names and the subnets of all of the interfaces available on the local node
by executing the iflist keyword as shown in this example:
oifcfg iflist
hme0 139.185.141.0
qfe0 204.152.65.16
You can also retrieve specific OIFCFG information with a getif command using the following syntax:
oifcfg getif [ [-global | -node nodename] [-if if_name[/subnet]] [-type if_type] ]
To store a new interface use the setif keyword. For example, to store the interface hme0, with the subnet
139.185.141.0, as a global interface (to be used as an interconnect for all of the RAC instances in your cluster),
you would use the command:
oifcfg setif -global hme0/139.185.141.0:cluster_interconnect
For a cluster interconnect that exists between only two nodes, for example rac1 and rac2, you could create the cms0
interface with the following commands, assuming 139.185.142.0 is the subnet addresses for the interconnect on rac1
and rac2 respectively:
oifcfg setif -global cms0/139.185.142.0:cluster_interconnect
Use the OIFCFG delif command to delete the stored configuration for global or node-specific interfaces. A specific
node-specific or global interface can be deleted by supplying the interface name, with an optional subnet, on the
command line. Without the -node or -global options, the delif keyword deletes either the given interface or all of
the global and node-specific interfaces on all of the nodes in the cluster. For example, the following command
deletes the global interface named qfe0 for the subnet 204.152.65.0:
oifcfg delif -global qfe0/204.152.65.0
On the other hand, the next command deletes all of the global interfaces stored with OIFCFG:
oifcfg delif -global
15.What is the Purpose of the voting disk in Oracle 10g Clusterware?
Voting disk record node membership information. Oracle Clusterware uses the voting disk to determine which instances are members of a cluster. The voting disk must reside on a shared disk. For high availability, Oracle recommends that you have a minimum of three voting disks. If you configure a single voting disk, then you should use external mirroring to provide redundancy. You can have up to 32 voting disks in your cluster.
16.What is the purpose of the OCR in Oracle 10g Clusterware?
Ans: Oracle Cluster Registry (OCR) is a component in 10g RAC used to store the cluster configuration information. It is a shared disk component, typically located in a shared raw volume that must be accessible to all nodes in the cluster.
The daemon OCSSd manages the configuration info in OCR and maintains the changes to cluster in the registry.
17. In Oracle Streams archived log downstream capture, which database view can be used to determine which archived
logs are no longer needed by the capture process?
Ans: V$ARCHIVE_DEST_STATUS
SELECT col1 FROM tableA WHERE NOT IN (SELECT col1 FROM tableB);
Ans. SQL is incorrect.
Correct SQL : SELECT col1 FROM tableA WHERE col1 NOT IN (SELECT col1 FROM tableB);
2. What is a more efficient way to write this query, to archive the same set?
Ans: SELECT col1 from tableA minus SELECT col1 from tableB
3.How would you determine that the new query is more efficient than the original query?
Ans: Run explain plan on both query and see the result .
4.How can we find the location of the database trace files from within the data dictionary?
Ans: Generally trace file on the database server machine is located in one of two locations:
1. If you are using a dedicated server connection, the trace file will be generated in the directory specified by
the USER_DUMP_DEST parameter.
2.If you are using a shared server connection, the trace file will be generated in the directory specified by the
BACKGROUND_DUMP_DEST parameter.
you can run sqlplus>SHOW PARAMETER DUMP_DEST
or
select name, value
from v$parameter
where name like '%dump_dest%'
5. What is the correct syntax for a UNIX endless WHILE loop?
while :
do
commands
done
6. Write the SQL statement that will return the name and size of the largest datafile in the database.
SQL> select name,bytes from v$datafile where bytes=(select max(bytes) from v$datafile);
7. What are the proper steps to changing the Oracle database block size?
cold backup all data files and backup controlfile to trace, recreate your database
with the new block size using the backup control file, and restore. It may be easier
with rman. You can not change datbase block size on fly.
8. Using awk, write a script to print the 3rd field of every line.
Ans:
awk
awk '{print $3}
awk '{print $3}
9.Under what conditions, is a nested loop better than a merge join?
Ans:
Optimizer uses nested loop when we are joining tables containing small number of rows with an efficient driving
condition.
It is important to have an index on column of inner join table as this table is probed every time for a new value
from outer table.
Optimizer may not use nested loop in case:
1. No of rows of both the table is quite high
2. Inner query always results in same set of records
3. The access path of inner table is independent of data coming from outer table.
merge join is used to join two independent data sources. They perform better than nested loop when the volume of
data is big in tables
but not as good as hash joins in general.
10.Which database views would you use to ascertain the number of commits a user's session has performed?
Joining V$SESSTAT ,V$STATNAME
select * from V$SESSTAT a ,V$STATNAME b where b.CLASS=a.STATISTIC# and b.NAME='user commits' and a.sid=
11.What does the #!bin/ksh at the beginning of a shell script do? Why should it be there?
Ans: On the first line of an interpreter script, the "#!", is the name of a program which should be used to
interpret the contents of the file.
For instance, if the first line contains "#! /bin/ksh", then the contents of the file are executed as a korn shell
script.
12.What command is used to find the status of Oracle 10g Clusterware (CRS) and the various components it manages
(ONS, VIP, listener, instances, etc.)?
Ans:
$ocrcheck
13.Describe a scenario in which a vendor clusterware is required, in addition to the Oracle 10g Clusterware.
If you choose external redundancy for the OCR and voting disk, then to enable redundancy, the disk subsystem must be configurable for RAID mirroring/vendor clusterware. Otherwise, your system may be vulnerable because the OCR and voting disk are single points of failure.
14.How would you find the interconnect IP address from any node within an Oracle 10g RAC configuration?
using oifcfg command.
se the oifcfg -help command to display online help for OIFCFG. The elements of OIFCFG commands, some of which are
optional depending on the command, are:
*nodename—Name of the Oracle Clusterware node as listed in the output from the olsnodes command
*if_name—Name by which the interface is configured in the system
*subnet—Subnet address of the interface
*if_type—Type of interface: public or cluster_interconnect
You can use OIFCFG to list the interface names and the subnets of all of the interfaces available on the local node
by executing the iflist keyword as shown in this example:
oifcfg iflist
hme0 139.185.141.0
qfe0 204.152.65.16
You can also retrieve specific OIFCFG information with a getif command using the following syntax:
oifcfg getif [ [-global | -node nodename] [-if if_name[/subnet]] [-type if_type] ]
To store a new interface use the setif keyword. For example, to store the interface hme0, with the subnet
139.185.141.0, as a global interface (to be used as an interconnect for all of the RAC instances in your cluster),
you would use the command:
oifcfg setif -global hme0/139.185.141.0:cluster_interconnect
For a cluster interconnect that exists between only two nodes, for example rac1 and rac2, you could create the cms0
interface with the following commands, assuming 139.185.142.0 is the subnet addresses for the interconnect on rac1
and rac2 respectively:
oifcfg setif -global cms0/139.185.142.0:cluster_interconnect
Use the OIFCFG delif command to delete the stored configuration for global or node-specific interfaces. A specific
node-specific or global interface can be deleted by supplying the interface name, with an optional subnet, on the
command line. Without the -node or -global options, the delif keyword deletes either the given interface or all of
the global and node-specific interfaces on all of the nodes in the cluster. For example, the following command
deletes the global interface named qfe0 for the subnet 204.152.65.0:
oifcfg delif -global qfe0/204.152.65.0
On the other hand, the next command deletes all of the global interfaces stored with OIFCFG:
oifcfg delif -global
15.What is the Purpose of the voting disk in Oracle 10g Clusterware?
Voting disk record node membership information. Oracle Clusterware uses the voting disk to determine which instances are members of a cluster. The voting disk must reside on a shared disk. For high availability, Oracle recommends that you have a minimum of three voting disks. If you configure a single voting disk, then you should use external mirroring to provide redundancy. You can have up to 32 voting disks in your cluster.
16.What is the purpose of the OCR in Oracle 10g Clusterware?
Ans: Oracle Cluster Registry (OCR) is a component in 10g RAC used to store the cluster configuration information. It is a shared disk component, typically located in a shared raw volume that must be accessible to all nodes in the cluster.
The daemon OCSSd manages the configuration info in OCR and maintains the changes to cluster in the registry.
17. In Oracle Streams archived log downstream capture, which database view can be used to determine which archived
logs are no longer needed by the capture process?
Ans: V$ARCHIVE_DEST_STATUS
Subscribe to:
Post Comments (Atom)
Blog Archive
-
▼
2008
(277)
-
▼
September
(261)
- Setting oracle database in archive mode from non-a...
- Oracle Version Information - How to CheckYour Curr...
- Database and Instance Shutdown
- Database and Instance Shutdown
- What Happens When You Open a Database
- How to Identify Your Oracle Database Software Release
- What is block change tracking in RMAN Oracle 10g
- What is Incremental Merge in RMAN 10g?
- Moving from DBMS_JOB to DBMS_SCHEDULER
- Moving from DBMS_JOB to DBMS_SCHEDULER
- Moving from DBMS_JOB to DBMS_SCHEDULER
- Moving from DBMS_JOB to DBMS_SCHEDULER
- Oracle Database 10g Scheduler - Associating Jobs w...
- Oracle Database 10g Scheduler - Creating Jobs With...
- Oracle Database 10g Scheduler
- DBMS_JOB Package
- Data Guard Database Synchronization Options
- Data Guard Role Management
- Data Guard Broker
- Data Guard Protection Modes
- Redo Apply and SQL Apply
- Data Guard Benefits
- Creating a Nested Materialized View: Example
- Creating a Fast Refreshable Materialized View: Exa...
- Automatic Refresh Times for Materialized Views: Ex...
- Periodic Refresh of Materialized Views: Example
- Creating Rowid Materialized Views: Example
- Creating Primary Key Materialized Views: Example
- Creating Subquery Materialized Views: Example
- Creating Prebuilt Materialized Views: Example
- Creating Materialized Join Views: Example
- Creating Materialized Aggregate Views: Example
- Privilages to create a refresh-on-commit materiali...
- Privilages to create a materialized view in anothe...
- What Privilages required to create a materialized ...
- What is materialized view?
- What is Optimizer Plan Stability?
- DBMS_ADVISOR Package
- What is Bigfile tablespace? why do we create it? w...
- Reverting a Table to its Previous Statistics
- Manipulating Statistics Using DBMS_STATS
- Copying Statistics Using DBMS_STATS
- Gathering statistics with DBMS_STAT Package
- Handling Errors During Backups: Example
- Backup Validation with RMAN
- Detection of Logical Block Corruption
- Detecting Physical and Logical Block Corruption
- Tests and Integrity Checks for Backups?
- When RMAN Performs Control File Autobackups
- How RMAN Performs Control File Autobackups?
- what command do you execute to ensure that the con...
- Which background processes coordinates the rebalan...
- Which background processes coordinates the rebalan...
- What is oracle ASM in Oracle 10g? How do we create...
- Load Balancing In Oracle 10g Real Application Clus...
- Oracle 10gR2 load balancing - Server side load bal...
- Oracle 10gR2 load balancing- Client-Side Connectio...
- Oracle 10gR2 load balancing - Part2 - Client-Side ...
- Oracle 10gR2 load balancing - Part1
- Oracle database tuning without any tools - using p...
- Oracle database tuning without any tools - using p...
- Oracle database tuning without any tools - using p...
- Oracle database tuning without any tools - using p...
- Quick DBA Test - Oracle 10g
- what are the major new featurs in Oracle 10g data ...
- Flashback version query in oracle 10g
- Optimizing Performance of Direct Path Loads
- Data Conversion During Direct Path Loads
- Data Loading Methods - SQL Loader
- How Does Data Pump Access Data?
- Oracle data pump 10g impdp help
- Oracle data pump 10g expdp help
- Exporting and Importing External tables using Data...
- Oracle 10g Data Pump APIs
- Difference between old exp/imp and new data pump e...
- Oracle Data pump 10g getting started
- Oracle Data Pump in Oracle Database 10g
- What is FLASHBACK TABLE ? Explain with examples?
- What is Oracle Secure Backup (OSB)?
- What is auxiliary instance? when it is created?
- Automatic Instance Creation for RMAN TSPITR
- Oracle 10 RMAN Views
- How to setup RMAN in Oracle 9i
- What is block pinging and why is it so bad?
- Can I test if a database is running in RAC mode?
- How does one stop and start RAC instances?
- How does one convert a single instance database to...
- How many OCR and voting disks should one have?
- Do you need special hardware to run RAC?
- Can any application be deployed on RAC?
- Oracle Real Application Clusters (RAC) FAQ - previ...
- Backup Scripts When Few Data Blocks Change
- Improving Incremental Backup Performance: Change T...
- Incrementally Updated Backups: A One Week Example
- Basic Incremental Backup Strategy
- Cumulative Incremental Backups
- Differential Incremental Backups
- Level 0 and Level 1 Incremental Backups
- RMAN Incremental Backups
- Using Compressed Backupsets
-
▼
September
(261)
Posts
No comments:
Post a Comment