Setting the ARCHIVE_LAG_TARGET Initialization Parameter
When you set the ARCHIVE_LAG_TARGET initialization parameter, you cause Oracle to examine an instance's current online redo log periodically. If the following conditions are met the instance will switch the log:
The current log was created prior to n seconds ago, and the estimated archival time for the current log is m seconds (proportional to the number of redo blocks used in the current log), where n + m exceeds the value of the ARCHIVE_LAG_TARGET initialization parameter.
The current log contains redo records.
In an Oracle Real Application Clusters environment, the instance also nudges other threads into switching and archiving logs if they are falling behind. This can be particularly useful when one instance in the cluster is more idle than the other instances (as when you are running a 2-node primary/secondary configuration of Oracle Real Application Clusters).
Initialization parameter ARCHIVE_LAG_TARGET specifies the target of how many seconds of redo the standby could lose in the event of a primary shutdown or crash if the Data Guard environment is not configured in a no-data-loss mode. It also provides an upper limit of how long (in the number of seconds) the current log of the primary database can span. Because the estimated archival time is also considered, this is not the exact log switch time.
The following initialization parameter setting sets the log switch interval to 30 minutes (a typical value).
ARCHIVE_LAG_TARGET = 1800
A value of 0 disables this time-based log switching functionality. This is the default setting.
You can set the ARCHIVE_LAG_TARGET initialization parameter even if there is no standby database. For example, the ARCHIVE_LAG_TARGET parameter can be set specifically to force logs to be switched and archived.
ARCHIVE_LAG_TARGET is a dynamic parameter and can be set with the ALTER SYSTEM SET statement.
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