Hi,

I will continue to tell Oracle Dataguard Architecture in this post.

Oracle Dataguard ( Standby ) Architecture

Read first article before this article.

Oracle Dataguard ( Standby ) Architecture -1

Data Guard has 2 different modes of operation: Synchronous and Asynchronous.

We can explain 2 different ways of Data Guard According to the architecture above on a Transaction as follows:

Synchronous Data Guard

1. When a Transaction is started in the database, it is first written to the Redo Buffer section. When user commits the transaction, the LGWR process writes the redo data in the Redo Buffer field to the Online Redo Logs then LNS process waits for the verification that redo data is written to the Standby database.
2. The LNS (Log Network Service) process reads the same Redo data from the Redo Buffer section and reports to the RFS (Remote File Service) process via the ONS (Oracle Net Service). The LNS process automatically reads the Online redo logs of the Primary database if the corresponding Redo data cannot be accessed from Redo Buffer.
3. RFS Process writes Redo data ( coming from LNS ) to the Standby Redo Logs.
4. Managed Recovery Process uses the Redo data from the Standby Redo Logs and applied to the Standby database.
5. Finally, RFS process sends confirmation that sent redo data has been successfully written to the Standby. LNS process sends the message to the LGWR process and then user is now informed that the Commit operation is successful.

Asynchronous Data Guard

1. When a Transaction is started in the database, it is first written to the Redo Buffer section. When this transaction is committed, the LGWR process writes Redo Data from Redo Buffer section to the Online Redo Logs.
2. The LNS (Log Network Service) process reads the same Redo data from the Redo Buffer section and reports to the RFS (Remote File Service) process via the ONS (Oracle Net Service). The LNS process automatically reads the Online redo logs of the Primary database if the corresponding Redo data cannot be accessed from Redo Buffer.
3. RFS Process writes Redo data ( coming from LNS ) to the Standby Redo Logs.
4. Managed Recovery Process uses the Redo data from the Standby Redo Logs and applied to the Standby database.

In the Asynchronous Dataguard method, confirmation that the RFS process has successfully processed the redo data is not sent to the LNS, so there is no loss of Zero data and the data is recovered with minimal data loss.

In the Synchronous Dataguard method, this method guarantees zero data loss because all the data that has been committed is sent to the Standby side and it is guaranteed to be applied.

However, there are some problems with Synchronous according to Asynchronous Synchronous Data Guard, less performance than the Asynchronous Data Guard method because in the Synchronous Data guard method, the LGWR process always waits for the verification from the LNS process and Leads to loss of time. However,  Zero Data Loss Solution is more advantageous than the Asynchronous method in the very critical databases.

Oracle Dataguard technology provides us with 3 protection modes according to different options for protecting our data. We will explain what these are in the next post.

Click the followin link to open the next post.

Oracle Dataguard ( Standby ) Architecture -3

If you want to learn how to install Dataguard, you can read the following post.

Oracle DataGuard Physical Standby Installation Step by Step Using RMAN -2

Do you want to learn Oracle Database for Beginners, then read the following articles.

Oracle Tutorial | Oracle Database Tutorials for Beginners ( Junior Oracle DBA )