Oracle Database Synchronization Technology

Oracle Database-based data synchronization technology can be divided into two types: data synchronization technology provided by Oracle itself and data synchronization technology provided by third-party vendors. Oracle's own synchronization technologies include DataGuard, Streams, Advanced Replication, and a recently acquired data synchronization software called GoldenGate this year. Third-party manufacturers' data synchronization technologies include SharePlex of Quest and RealSync of DSG. We will introduce these technologies one by one.

I. DataGuard Data Synchronization Technology

DataGuard is a data synchronization function provided by the Oracle database. The basic principle is to transfer log files from the original database to the target database, and then Apply these log files to the target database, in this way, the target database is synchronized with the source database. Mongouard provides three log transmission modes: ARCH transmission, LGWR synchronous transmission, and LGWR asynchronous transmission. Based on the preceding three log transmission modes, three data Protection modes are provided: Maximum Performance Mode and Maximum Protection Mode) and Maximum Availability Mode. The Maximum protection Mode and Maximum available Mode require that the log transmission must be in LGWR synchronous transmission Mode, and any log transmission Mode is available in the Maximum performance Mode.

Maximum performance mode: This mode is the default data protection mode, which provides the highest possible data protection level 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. If the network bandwidth is sufficient, this mode provides a data protection level similar to the maximum available mode.

Maximum protection mode: In this mode, the log data must be written to the online log file of the source database and the standby log file (standby redo log) of at least one target database at the same time before the transaction can be committed. This mode ensures zero data loss, but the cost is the availability of the source database. Once the log data cannot be written to at least one standby log file (standby redo log) of the target database ), the source database will be disabled. This is the only data synchronization solution on the market to ensure zero data loss.

Maximum available mode: This mode provides the highest possible data protection level without sacrificing the availability of the source database. Like the maximum protection mode, transactions can be committed only when log data is written to the online log file of the source database and the standby log file (standby redo log) of at least one target database at the same time, unlike the maximum protection mode, if the log data cannot be written to the standby log file (standby redo log) of at least one target database, the source database will not be closed, it runs in the maximum performance mode. After the fault is resolved and the delayed logs are successfully applied to the target database, the source database will automatically return to the maximum available mode.

Based on the different Log Apply methods in the target database, mongouard can be divided into Physical Standby (Redo Apply) and Logical Standby (SQL Apply.

Physical Standby database, in this way, the http://www.bkjia.com target database maintains synchronization with the source database through media recovery, which supports any type of data objects and data types, some operations on the physical structure of the database, such as adding or deleting data files, are also supported. If necessary, the Physical Standby database can be opened in read-only mode for REPORT query, data verification, and other operations. After these operations are completed, the database is placed in log application mode.

Logical Standby database. In this way, the target database is open. LogMiner is used to mine logs transmitted from the source database, construct SQL statements, and execute these SQL statements on the target database, to keep it synchronized with the source database. Because the database is in the open state, you can put the query and report operations originally executed in the source database into the target database while updating the database using SQL Apply, to reduce the pressure on the source database and improve its performance.

DataGuard data synchronization technology has the following advantages:

1) the built-in functions of the Oracle database are fully compatible with new features (such as ASM) of each new version of Oracle and do not need to be paid separately;

2) easy configuration management, and no need to be familiar with third-party software products;

3) The Physical Standby Database supports all types of data objects and data types;

4) the Logical Standby database is open and can be queried while data synchronization is maintained;

5) in the maximum protection mode, zero data loss can be ensured;

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