Oracle Learning Dataguard (i) DG Architecture

The Dataguard operation principle is very simple: transfer logs, application logs. Represents the basic architecture of DG

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1. The Log Transport service uploads the log data generated by the main library to the slave library.

2. The app service validates the log data and updates the data files from the library.

3. The write process of the primary database updates the data file and does not depend on the Dataguard schema.

4. When the network or from the library fails to recover, the DG automatically retransmit the log data that has been archived by the main library.

• Log Transport service Redo Transport Services

Redo Transport Services coordinates log transfers between master and slave libraries. When the main library LGWR writes logs, the log Network Server (LNS) program reads logs data from the log buffer cache and transmits data to the slave library via Oracle Net services. Incoming logs are received from remote File Server (RFS) on the library. RFS writes the received log to the standby redo log file (SRL). In a multi-library environment, the main library enables a separate LNS process for each slave library to transfer log data.

Using the LNS process, Dataguard supports two types of log transfers: synchronous, asynchronous.

Synchronous log transfer Synchronous Redo Transport

Synchronous Transport (SYNC) is also known as "0 data loss". A commit operation on the main library is considered successful only if the LNS confirms that the log is transferred to the library and has been written to disk.

Data Guard Log Transport Process schema

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SYNC Redo Transport Architecture

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1. The user commits a transaction and will generate some redo record in redo buffer. LGWR reads the Redo record from log buffer and writes it to the online Redo Logs, while awaiting confirmation from the LNS process.

2. LNS reads the same redo record from redo buffer and transmits it to the slave library via ONS. RFS receives the log and writes it to standby Redo Logs.

3. When the RFS log succeeds, a confirmation signal is transmitted to the LNS,LNS on the main library informing LGWR of this acknowledgment. At this time LGWR can feedback to the user to submit the successful information.

This article is from the "Ding Dong" blog, please be sure to keep this source http://lqding.blog.51cto.com/9123978/1681073

Oracle Learning Dataguard (i) DG Architecture