Oracle Data Guard Learning (2) Log transfer

Oracle Data Guard from the macroscopic point of view, mainly provides the following two services:

1) Log transmission: The main library transmits the generated redo log to the standby library;

2 log application: The redo log, which is transferred from the main library, is used by the standby library.

This article first describes the log Transport service, the log application service in the next section of the Data Guard series (3)-log application.

1. Log transmission mode

There are two types of log transmissions (arc and LGWR), the first of which is the use of the ARC process to transfer logs, the following schematic diagram:

Note: The above image from "Dahua Oracle RAC"

The approximate process is as follows:

1 Main Library: Log first written online redo log, when the online redo log full (after human switching), ARC0 process Archive the log to the main library local archive directory, after the archive is completed, ARC1 immediately transfer the archive log to the standby;

2 Prepare the Library: RFS process to receive the log, if the repository has standby redo log, then copy the log to the standby redo log, and then the standby Redo log archive to the standby local archive directory, the final application of the archive log; If you do not configure the standby redo log, After the RFS process receives the log, it is placed directly in the archive directory of the standby and then applied to the log.