Dg_oracle Dataguard function and concept (concept)

2014-06-03 Created by Baoxinjian

I. Summary

Oracle Dataguard is an Oracle-brought data synchronization feature that transfers log files from the original database to the target database and then applies the log files on the target database to keep the target database synchronized with the source database, which is a database-level high availability scenario.

Dataguard can provide Oracle database redundancy, data protection, failure recovery, and so on to achieve rapid database switching and catastrophic recovery. When transactional consistency is guaranteed in the production database, a standby is created using a physical full backup of the production library, which automatically maintains an alternate database through an archive log or redo entry that is transmitted over the production library.

Dataguard Data synchronization technology has the following advantages:

1. The features built into the Oracle database itself are fully compatible with the new features of each Oracle new version, and do not require an additional fee.

2. Configuration management is simple and does not require familiarity with other third-party software products.

3. The physical standby database supports any type of data object and data type;

4. The logical standby database is open to perform operations such as querying while keeping data synchronized.

5. In maximum protection mode, you can ensure that 0 of the data is lost.

Second, the structure

Oracle Dataguard consists of a primary database (production database) and one or more standby databases (up to 9). The database that makes up data guard is connected through Oracle NET and can be distributed across different geographies.

As long as the libraries can communicate with each other, their physical location is not limited by the operating system.

1.Primary Database

The Dataguard contains a primary database, which is a production database accessed by most applications, which can be either a single-instance database or a RAC.

The 2.Standby database Standby database is a replication of the primary database (transactionally consistent). You can create up to 9 standby databases in the same data guard. Once created, Data guard automatically maintains each standby database by applying the redo of the primary database.

The standby database can also be a single-instance database or a RAC structure.

Ii.. Standby database type

Standby databases are usually divided into two categories: logical standby and physical standby.

Logic standby

The logical standby is to synchronize by receiving the redo log of the primary database and converting it into an SQL statement, and then executing the SQL statement on the standby database.

Physical standby

The physical standby is synchronized by receiving and applying the redo log of the primary database in the form of media recovery, not only the physical structure of the file, but also the storage location of the block on the disk is identical.

Third, the service

1. Redo Transfer Service (Redo Transport Services)

Control the transmission of redo data to one or more archived destinations.

2. Log Application Service (logs apply services)

Apply redo data to the standby database to maintain consistency with the transactions of the primary database. The redo data can be read from an archive file in the standby database or directly by applying an alternate log file.

3. Role conversion Service (roles transitions)

There are two types of roles in Dataguard: Primary and Standby. The role transformation is to have the database switch between the two roles,

There are two types of switching: switchover and failover

1) Switchover:

Convert the primary database to the standby database.

Switchover can ensure that data is not lost.

2) Failover:

When the primary database fails and cannot be restored in a timely manner, it calls failover to convert a standby database into a new primary database. In maximum protected mode or highest availability mode, the failover guarantees that no data loss is possible.

Iv. Mode of protection

1. Maximum protection

This mode is the default data protection mode, providing the highest possible level of data protection without affecting the performance of the source database.

In this mode, once the log data is written to the online log file of the source database, the transaction can be committed without waiting for the log to be written to the target database, and if the network bandwidth is sufficient, the mode provides a level of data protection similar to the maximum available mode.

2. Maximum Availability

This model is basically the same as "maximum protection". Under normal circumstances, the master repository is synchronized.

When there is a problem with the network or the standby, it will not affect the main library's machine, the main library will automatically convert the library "maximum performance" mode, wait for the repository to be available, transfer the archive to the standby for recovery.

3. Maximum Performance

This mode ensures maximum performance of the main library, and the data is transmitted asynchronously between the main repositories. That is, the primary and standby logs are archived and then transferred to the standby library, and the archive log file is used for recovery operations on the standby.

Five, installation conditions

The following conditions are required to run Dataguard:

1. The same version of Oracle Enterprise Edition must be installed on all machines in the main library and from the library.

2. The main library must be running in archive mode.

3, the main library and the operating system from the library must be the same (allow different versions), from the library can use a different directory structure than the main library.

4, the master-slave library hardware system architecture must be the same. For example: The main library is running on a 64-bit sun SPARC system, which is not allowed if the Linux Intel system is 32-bit from the library. The configuration of the master-slave library hardware can be different, such as: Number of CPUs, memory size, storage configuration, etc.

Thanks and regards

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Dg_oracle Dataguard function and concept (concept)