[Oracle] Data Guard-Redo Transmission

[Oracle] Data Guard-Redo transmission Data Guard mainly provides two services: 1) Redo transmission service: Transfers Redo logs of the Primay end to one or more Standby destinations. 2) Redo Application Service: The Redo log transmitted from Primay on the Standby side. This article describes the Redo transmission service. 1. By default, ARCn is used to transmit Redo logs using ARCn. However, ARCn can only be used in the highest-performance mode. The following describes how to transmit redo logs using ARCH: the general process is as follows: 1) Once the log switching is completed for the Primay segment ARC0, ARC1 transfers the newly generated archive log to the Standby end; 2) the Standby end receives the log from the RFS process, if the standby redo log is configured, it is recorded to the standby redo log. When the standby redo log is used as the log switch, archive logs are applied for recovery. If the standby redo log is not configured, after the RFS process receives logs, it stores them in the archive directory of the standby end, and then applies the archived logs for recovery. 2. Using LGWR to transmit Redo logs the LGWR process is very different from that of ARCn. The most obvious difference is that it does not need to wait for the Primary to complete the log switching and then transmit the logs, as shown below: the process is roughly as follows: 1) Once a Redo log is generated in Primary, LGWR will trigger the LNSn process to transmit Redo logs only Standby redo logs. Note: LGWR cannot directly transmit the logs here, because the entire database instance has only one LGWR, in order to ensure its primary performance is not affected, it cannot be directly transmitted) 2) the network transmission mode can be sync or async, sync means that when the Primary is submitted, it must wait until the Redo is successfully transferred to Standby before returning it. Therefore, if sync is set, we recommend that you set the NET_TIMEOUT parameter at the same time. If no response is returned during timeout, an error is returned. Async means that whether the submission of Primary is successful has nothing to do with whether the log is successfully transferred. This minimizes the impact on the performance of Primary. 3) The RFS process at the Standby end writes Redo to the Standby redo log. If real-time applications are enabled, the redo log is applied to the Standby database. If real-time applications are not enabled, wait until the Standby redo log is archived and then applied to the Standby database.