Scenario 16: Using the Observe-only Mode for Fast-Start Failover

The observe-only mode enables you to test the impact of using fast-start failover in your configuration, without making any actual changes to the configuration. You can use the DGMGRL commands or data dictionary views to verify the observe-only mode setting.

Topics:

Configuring Observe-only Mode for Fast-Start Failover

Use the ENABLE FAST_START FAILOVER command to configure observe-only mode for fast-start failover.

  1. Use the following command to configure the observe-only mode for fast-start failover.
    DGMGRL> ENABLE FAST_START FAILOVER OBSERVE ONLY;

    All existing observers and ones that will be started in the future will run in observe-only mode.

  2. Verify that the observe-only mode has be set by using one of the following methods:

    1. Display the current fast-start failover configuration using the following command:

      DGMGRL> SHOW FAST_START FAILOVER;
Fast-Start Failover: Enabled in Observe-Only Mode

  Protection Mode: MaxAvailability
  Lag Limit: 30 seconds

  Threshold: 30 seconds
  Ping Interval: 3000 milliseconds
  Ping Retry: 0
  Active Target: South_Sales
  Potential Targets: "South_Sales"
    South_Sales valid
  Observer: observer.example.com
  Shutdown Primary: TRUE
  Auto-reinstate: TRUE
  Observer Reconnect: (none)
  Observer Override: FALSE

    2. Display the current fast-start failover mode using the following command:

      SQL> SELECT fs_failover_mode from V$DATABASE;

FS_FAILOVER_MODE
-------------------
OBSERVE-ONLY

Sample Content of the Log Files in Observe-only Mode

This section shows the entries made to the log files when you configure fast-start failover in observe-only mode.

Example 1: When Fast-start Failover Should be Initiated

Observer Log

A fast-start failover would have been initiated...
Unable to failover since this observer is in observe-only mode

Broker Log

Fast-Start Failover cannot proceed because: "observe-only mode"

Example 2: Primary Database Opens During Startup Without an Acknowledgement from Observer or Target Standby

The broker log file (drc*.log) and alert log contain the following:

This database is allowed to open in observe-only mode. An acknowledgement from observer or target standby would have been required in normal FSFO mode.

Example 3: Switchover or Manual Failover to a Bystander Database

The broker log file (drc*.log) and alert logs contain the following information:

FAILOVER to database 'database name' is allowed even though observe-only mode is enabled. It would have been rejected since database 'database name' is a bystander database.

Disabling Observe-only Mode for Fast-start Failover

Use the DISABLE FAST_START FAILOVER command to exit the observe-only mode of fast-start failover. You must first disable fast-start failover and then enable fast-start failover without the OBSERVE ONLY clause.

Use the following commands to disable observe-only mode for fast-start failover: 

DGMGRL> DISABLE FAST_START FAILOVER;
DGMGRL> ENABLE FAST_START FAILOVER;

Fast-start failover is now enabled, without observe-only mode.