Oracle Dataguard - Quick Learn

iDBA , An iphone App for Oracle DBA's DownLoad To Day !!!

Oracle Dataguard - Quick Learn

A Data Guard configuration contains a primary database and up to nine associated standby databases.

What is a Standby database ?

A standby database is a transactionally consistent copy of an Oracle production

database that is initially created from a backup copy of the primary database. Once the

standby database is created and configured, Data Guard automatically maintains the

standby database by transmitting primary database redo data to the standby system,

where the redo data is applied to the standby database.

What are the types of standby databases?

A standby database can be one of these types: a physical standby database, a logical standby database, or a snapshot standby database. A Data Guard configuration can include any combination of these types of standby databases.

What is the use of a standby database?

Standby database can assume the role of the primary database and take over

production processing.

What is a Physical standby database and mention its benefits?

A physical standby database is an exact, block-for-block copy of a primary database.A physical standby is maintained as an exact copy through a process called Redo Apply,in which redo data received from a primary database is continuously applied to a physical standby database using the database recovery mechanisms.A physical standby database provides the following benefits:

1) Disaster recovery and high availability

2) Data protection

3) Reduction in primary database workload

4) Performance(as redo apply bypass all SQL level code layers

What is a Logical standby database?

Data Guard applies information from the archived redo log file or standby redo log file to the logical standby database by transforming the data in the log files into SQL statements and then executing the SQL statements on the logical standby database. Because the logical standby database is updated using SQL statements, it must remain open. Although the logical standby database is opened in read/write mode, its target tables for the regenerated SQL are available only for read-only operations. While those tables are being updated, they can be used simultaneously for other tasks such as reporting, summations, and queries. Tthese tasks can be optimized by creating additional indexes and materialized views on the maintained tables.

What are the benefits of a Logical standby database?

A logical standby database is ideal for high availability (HA) compared to physical standby database and provides following benefits:

1) Logical standby analyzes the redo and reconstructs logical changes to the database, it can detect and protect against certain kinds of hardware failure on the primary that could potentially be replicated through block level changes.

2)A logical standby database is open read/write while changes on the primary are being replicated and hence can be used to run reporting workloads, test new software releases and some kinds of applications on a complete and accurate copy of the primary’s data.It can host other applications and additional schemas while protecting data replicated from the primary against local changes.It can be used to assess the impact of certain kinds of physical restructuring (for example, changes to partitioning schemes). Because a logical standby identifies

user transactions and replicates only those changes while filtering out background system changes, it can efficiently replicate only transactions of interest.

3) Logical standby provides a simple solution for creating up-to-the-minute,consistent replicas of a primary database that can be used for workload distribution. As the reporting workload increases, additional logical standbys can be created with transparent load distribution without affecting the transactional throughput of the primary server.

4) A key benefit of logical standby is that significant auxiliary structures can be created to optimize the reporting workload; structures that could have a prohibitive impact on the primary’s transactional response time. A logical standby can have its data physically reorganized into a different storage type with different partitioning, have many different indexes, have on-demand refresh materialized views created and maintained, and it can be used to drive the creation of data cubes and other OLAP data views.

5) Logical standby can be used to greatly reduce downtime associated with applying patchsets and new software releases. A logical standby can be upgraded to the new release and then switched over to become the active primary. This allows full availability while the old primary is converted to a logical standby and the patchset is applied.

What is a snapshot standby database?

A snapshot standby database receives and archives, but does not apply, redo data from its primary database. Redo data received from the primary database is applied when a snapshot

standby database is converted back into a physical standby database, after discarding all local updates to the snapshot standby database.

What are the benefits of a snapshot standby database?

1)A snapshot standby database is a fully updatable standby database that provides disaster recovery and data protection benefits that are similar to those of a physical standby database

2)It provides an exact replica of a production database for development and testing purposes, while maintaining data protection at all times

3) It can be easily refreshed to contain current production data by converting to a physical standby and resynchronizing

http://oraclesource.weebly.com