12c ADG 延迟告警，延迟消失后，告警自动消失。
DGMGRL> show configuration;
Configuration - dg_config
Protection Mode: MaxPerformance
Members:
orcldg - Primary database
orcl - Physical standby database
Warning: ORA-16857: standby disconnected from redo source for longer than specified threshold
Fast-Start Failover: DISABLED
Configuration Status:
WARNING (status updated 41 seconds ago)
DGMGRL> exit
$oerr ora 16857
16857,0000, "standby disconnected from redo source for longer than specified threshold"
// *Cause: The amount of time the standby was disconnected from the
// redo source database exceeded the value specified by the
// 'TransportDisconnectedThreshold' database property. It is caused by
// no network connectivity between the redo source and the standby
// databases.
// *Action: Ensure that there is network connectivity between the redo source
// and standby databases, and the redo source is working properly.
$dgmgrl /
DGMGRL for Linux: Version 12.1.0.2.0 - 64bit Production
Copyright (c) 2000, 2013, Oracle. All rights reserved.
Welcome to DGMGRL, type "help" for information.
Connected as SYSDG.
DGMGRL> show configuration;
Configuration - dg_config
Protection Mode: MaxPerformance
Members:
orcldg - Primary database
orcl - Physical standby database
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS (status updated 20 seconds ago)
DGMGRL>
说明：
The Data Guard broker also has configurable database properties that can be used to generate warnings when a transport or apply lag exceed a user defined value:
The ApplyLagThreshold configurable database property generates a warning status for a logical or physical standby when the database's apply lag exceeds the value specified by the property. The property value is expressed in seconds. A value of 0 seconds results in no warnings being generated when an apply lag exists. As a best practice, Oracle recommends setting ApplyLagThreshold to at least 15 minutes.
The TransportLagThreshold configurable database property can be used to generate a warning status for a logical, physical, or snapshot standby when the database's transport lag exceeds the value specified by the property. The property value is expressed in seconds. A value of 0 seconds results in no warnings being generated when a transport lag exists. As a best practice, Oracle recommends setting TransportLagThreshold to at least 15 minutes.
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