Analysis and demonstration of Data Guard protection mode

In some cases, some businesses cannot tolerate data loss. In other cases, Database Availability may be more important than data loss. Some applications require the database to maximize performance and tolerate the loss of a little data. The following is a summary of the three different data protection modes.

The characteristics of the three modes in the following two figures are analyzed one by one:

1. Maximum protection)

This protection mode ensures that no data is lost when the master database fails. To provide this level of protection, the transaction involved in the redo log must be written to the standby redo log of the local online redo log and standby database (assuming there are multiple slave databases, to commit a transaction. To ensure that data is not lost, if a fault occurs that prevents the redo stream from writing at least one standby database with consistent transactions, the primary database will be closed.

As we can see from the above, to configure the maximum protection mode, we need to establish a standby redo log in the slave database, use LGWR to write logs, SYNC to synchronize logs, and affrem.

Parameter configuration instance:

Alter system set log_archive_dest_2 = 'service = db_phystdby lgwr sync VALID_FOR = (ONLINE_LOGFILES, PRIMARY_ROLE) DB_UNIQUE_NAME = PHYSTDBY affpem ';

2. Maximum availability)

This protection mode provides the highest level of data protection without affecting the availability of the master database. Like the maximum protection mode, the transaction involved in the redo log must be written to the standby redo log of the local online redo log and standby database (assuming there are multiple slave databases, to commit a transaction. However, unlike the maximum protection mode, if a fault occurs that prevents the redo stream from being written to a remote standby redo log, the master database will not close. Instead, the master database runs in the highest-performance mode until the fault is eliminated and the gaps (cracks) of the redo log file are eliminated. When all gaps are cleared, the master database automatically resumes running to the highest available mode.
This mode ensures that data will not be lost when the master database fails, but the second failure does not prevent the complete redo data from being sent from the master database to at least one slave database.
In this mode, like the maximum protection mode, standby redo logs need to be created in the slave database, logs are written using LGWR, logs are synchronized by SYNC, and affrem.
Parameter configuration instance:

Alter system set log_archive_dest_2 = 'service = db_phystdby lgwr sync VALID_FOR = (ONLINE_LOGFILES, PRIMARY_ROLE) DB_UNIQUE_NAME = PHYSTDBY affpem ';

3. Maximum performance (Maximum performance)

The highest-performance mode is the default protection mode, which provides the highest level of data protection without affecting the performance of the master database. In this mode, transaction commit is unrestricted. The redo data stream of the master database also requires writing at least one standby database, but the redo stream is not synchronized with the transaction that creates the redo data.
When the network bandwidth is sufficient, this mode provides database protection similar to the highest available mode, but has the lowest impact on the performance of the master database.
From the above analysis, we can use ARCH or LGWR in this mode.
If ARCH is used, SYNC is required ).
When LGWR is used, it can be SYNC or ASYNC.
Standby redo is dispensable.
Sample Configuration:
Alter system set log_archive_dest_2 = 'service = db_phystdby lgwr sync VALID_FOR = (ONLINE_LOGFILES, PRIMARY_ROLE) DB_UNIQUE_NAME = PHYSTDBY ';

References:

Important configuration parameters of Oracle Data Guard

Configure Oracle 11g Data Guard based on the same host

Explore Oracle 11g elastic uard

Oracle Data Guard (RAC + DG) archive deletion policies and scripts

Role conversion for Oracle Data Guard

FAL gap in Oracle Data Guard logs

Oracle 11g Data Guard Error 16143 Heartbeat failed to connect to standby

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