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9 Troubleshooting Oracle Data Guard

This chapter describes various errors and how to solve them. It contains the following topics:

9.1 Sources of Diagnostic Information

The Oracle Data Guard broker provides information about its activities in several forms:

  • Database status information (see Section 4.10)

  • Oracle alert log files

    The broker records key information in the alert log file for each instance of each database in a broker configuration. You can check the alert log files for such information when troubleshooting Oracle Data Guard.

  • Oracle Data Guard "broker log files"

    For each instance of each database in a broker configuration, the broker DMON process records important behavior and status information in a broker log file, useful in diagnosing Oracle Data Guard failures. The TraceLevel configuration property (see Section 8.1.10) is used to specify the level of diagnostic information reported in the broker log files.

    The broker log file is created in the same directory as the alert log and is named drc<$ORACLE_SID>.log.

  • Oracle Data Guard command line (DGMGRL) logfile

    If the DGMGRL command-line interface was started with the -logfile optional parameter (see Section 7.1.1), then the resulting log file may contain a useful record of past operations, error conditions, or both.

9.2 General Problems and Solutions

This section describes general problems and solutions. This section contains the following topics:

9.2.1 ORA-16596: database not part of the Oracle Data Guard broker configuration

A request was issued to the broker, but the database instance through which you have connected is no longer a part of the broker configuration.

Solution Reconnect to the configuration through another database that you know is part of the broker configuration. Confirm that a database exists in the broker configuration that has a name that matches the db_unique_name value of the database that returned the ORA-16596 error.

This problem can also occur if you attempt to enable a configuration, but the broker configuration file for one of its databases was accidentally removed or is outdated. In this case, remove the database from the broker configuration, manually delete the configuration file for that standby database (not for the primary database), and try again to enable the configuration. After the configuration is enabled, you can either use the Enterprise Manager Add Standby Database wizard and choose the Add existing standby database option, or you can use the DGMGRL command-line interface and issue the ADD DATABASE command.

9.2.2 Redo Accumulating on the Primary Is Not Sent to Some Standby Databases

By viewing the Log File Details page in Enterprise Manager, you have determined that log files are accumulating on the primary database and are not being archived to some of the standby databases in the broker configuration.

Solution To narrow down the problem, do the following:

  • Verify that the state of the primary database is in the TRANSPORT-ON state (not TRANSPORT-OFF).

  • Verify that the value of the LogShipping database property of the standby database in question is ON.

  • Check the status of the redo transport services on the primary database using the LogXptStatus monitorable property. If redo transport services have an error, then use the error message to determine further checking and resolution action. For example:

    • If the error indicates the standby database is not available, you need to restart the standby database.

    • If the error indicates no listener, you need to restart the listener.

    • If the error indicates the standby database has no local destination, you need to set up a standby location to store archived redo log files from the primary database.

9.2.3 Many Log Files Are Received on a Standby Database But Not Applied

By viewing the Performance page or Log File Details page in Enterprise Manager, you have determined that the standby database accumulates too many log files without applying them.

Solution There are many possible reasons why archived redo log files might not be applied to the standby database. Investigate why the log files are building up and rule out the valid reasons.

If the current status of the standby database is not normal:

  • Determine whether or not the log apply services might be unexpectedly stopped. See the ORA-16766 (for physical standby databases) or ORA-16768 (for logical standby databases) error description and solution statement for more help.

  • If this is a logical standby database, check to see if a failed transaction has occurred.

  • If you want to suppress the error while you investigate the problem, you can temporarily disable broker management of the database.

    See Also:

    Chapter 7 for additional information about disabling the database using the DGMGRL command-line interface

If the current status of the standby database is normal:

  • Verify the state of the standby database is APPLY-ON (not in the APPLY-OFF state).

  • Verify the state of the primary database is TRANSPORT-ON (not in the TRANSPORT-OFF state).

    See Also:

    Chapter 8 for additional information about the LogShipping database property
  • Check to see if log files are building up because the value of the DelayMins property is set too large. (Log apply services will delay applying the archived redo log files on the standby database for the number of minutes specified.)

    See Also:

    Chapter 8 for additional information about the DelayMins database property
  • If you cannot see any errors, compare the archive rate to the apply rate on the Performance page in Enterprise Manager to see if the apply rate is lower than the archive rate.

9.2.4 The Request Timed Out or Enterprise Manager Performance Is Sluggish

If the broker requests are not completing within the normal timeout parameters, try the following actions to solve the problem:

  1. Verify the network is operating appropriately.

  2. Try to ping all of the nodes in the configuration.

  3. Try reconnecting through another database to retry the operation.

  4. Run the VERIFY command to determine on which database the broker is unable to process the requests.

9.2.5 The Primary Database is Flashed Back

If the primary database is flashed back, the standby databases in the configuration must be also be flashed back or re-created to be viable targets for switchovers or failovers. The broker will report errors for the standby databases if the primary database has been flashed back.

For more information about restoring the viability of a standby database that was disabled by the broker, see Section 5.4.3.

9.2.6 Standby Fails to Automatically Start Up Due to Unknown Service (ORA-12514)

If the DGMGRL CLI fails to automatically start up an instance after a broker operation (for example, a switchover, reinstatement, convert to physical standby, or upgrade of protection mode to maximum protection mode), and you receive an ORA-12514: TNS:listener does not currently know of service requested in connect descriptor error, then you must manually start the instance to complete or continue the broker operation.

You can restart the instance before or after completing the following steps:

  1. Issue the following DGMGRL CLI command to check the value of the StaticConnectIdentifer configurable property for the instance the DGMGRL CLI was unable to restart. (You will have to connect to another running instance to issue this command):

    DGMGRL> SHOW INSTANCE VERBOSE 'instance_name' ON DATABASE db_unique_name;
    
  2. The static service name specified in the value of the StaticConnectIdentifer instance property should be registered with the listener specified in the property value. The default value for the static service name is of the following form:

    db_unique_name_DGMGRL.db_domain
    

    See Section 2.2 for more information about this, and other prerequisites, for using the broker.

  3. Confirm that the static service name is registered with the listener specified in the StaticConnectIdentifer configurable property value by using the Listener Control utility's status command. If the static service name is properly registered with the listener, it will be included in the output generated by the following command:

    lsnrctl status
    
  4. If you are working in an Oracle RAC environment, you may want to repeat steps 1 and 2 for each instance to ensure that a static service name is properly registered with its respective listener.

9.3 Troubleshooting Problems During a Switchover Operation

If the switchover fails due to problems with the configuration, then the broker reports any problems it encounters in the alert log files or in the broker log files (see Section 9.1). If the reported problems can be corrected, you can retry the switchover operation and it will usually succeed. If the reported problems cannot be corrected or the switchover operation fails even after correcting the reported problems, then you can choose another database for the switchover or restore the configuration to its pre-switchover state and then retry the switchover.

If fast-start failover is enabled, the broker does not allow switchover to any standby database except to the target standby database. In addition, switchover to the target standby database is allowed only when the value of the FS_FAILOVER_STATUS column in the V$DATABASE view on the target standby database is either READY or SUSPENDED.

9.4 Troubleshooting Problems During a Failover Operation

Although it is possible for a failover operation to fail, it is unlikely. If an error occurs, use the guidelines given in the following subsections to fix the problem and then retry the broker failover.

9.4.1 Failed Failovers to Physical Standby Databases

Use the steps below to recover from a failed broker failover to a physical standby database.

9.4.1.1 Failed Broker Complete Physical Failovers

Examine the alert and DRC log files on the target standby database to determine the cause of the failure and correct the problem. If the reported problem can be corrected, then retry the failover operation. If the reported problem cannot be corrected or if the failover operation fails again after the reported problem has been corrected, then take the following steps:

  1. Connect to the target standby database and disable fast-start failover using the FORCE option if it is enabled.

  2. Then you can either:

    • Connect to another physical standby database and attempt a broker complete failover.

    • Perform a broker immediate failover to the target physical standby database.

  3. Reinstate the original primary database and any bystander physical standby databases that are disabled with a status of reinstatement required (ORA-16661).

  4. Reenable fast-start failover if it was disabled in step 1.

9.4.1.2 Failed Broker Immediate Physical Failovers

Examine the alert and DRC log files on the target standby database to determine the cause of the failure and correct the problem. If the problem can be corrected, retry the broker immediate failover. Otherwise connect to another physical standby database and attempt either a broker complete or immediate failover.

9.4.2 Failed Failovers to Logical Standby Databases

  1. Examine the alert and DRC log files on the target standby database to determine the cause of the failure and correct the problem.

  2. Connect to the target standby database and disable fast-start failover using the FORCE option if it is enabled.

  3. Retry the broker failover.

  4. Reinstate the old primary database. All bystander standby databases will be re-created from a copy of the new primary database.

  5. Reenable fast-start failover if it was disabled in step 1.

If broker failover continues to fail, you should stop the broker on all databases in the Oracle Data Guard configuration (set the DG_BROKER_START initialization parameter to FALSE). Remove the Oracle Data Guard broker configuration files from all databases. Attempt a manual failover using the guidelines for role transitions in Oracle Data Guard Concepts and Administration.

Note:

You can enable or disable the broker configuration using DGMGRL ENABLE CONFIGURATION and DISABLE CONFIGURATION commands. You cannot disable the configuration using the Enterprise Manager. You can only enable the configuration using Enterprise Manager if it was previously disabled using DGMGRL.

9.5 Troubleshooting Problems with the Observer

The observer continuously monitors the fast-start failover environment to ensure the primary database is available. Installing and starting the observer is an integral part of using fast-start failover. The following sections describe techniques for troubleshooting the observer:

9.5.1 Problems Starting the Observer

Only one observer can be observing the broker configuration at any given time. If you attempt to start a second observer, one of the following errors is returned:

ORA-16647: could not start more than one observer
DGM-16954: Unable to open and lock the Observer configuration file

Use the DGMGRL SHOW CONFIGURATION VERBOSE command to determine the location of the observer that is currently associated with the broker configuration.

DGMGRL> SHOW CONFIGURATION VERBOSE;
 
Configuration - DRSolution
 
  Protection Mode: MaxAvailability
  Databases:
  North_Sales- Primary database
  South_Sales- Physical standby database
 
Properties:
  FastStartFailoverThreshold = '30'
  OperationTimeout = '30'
  TraceLevel = 'USER'
  FastStartFailoverLagLimit = '30
  CommunicationTimeout = '180'
  ObserverReconnect = '0'
  FastStartFailoverAutoReinstate = 'TRUE'
  FastStartFailoverPmyShutdown = 'TRUE'
  BystandersFollowRoleChange = 'ALL'
  ObserverOverride = 'FALSE'
 
Fast-Start Failover: ENABLED
 
  Threshold: 30 seconds
  Target: South_Sales
  Observer: observer.example.com
  Lag Limit: 30 seconds (not in use)
  Shutdown Primary: TRUE
  Auto-reinstate: TRUE
  Observer Reconnect: (none)
  Observer Override: FALSE
 
Configuration Status:
SUCCESS

9.5.2 Problems Because the Observer Has Stopped

If the observer host machine crashes, the broker configuration is no longer observed and fast-start failover is no longer possible. In this case, you may have to move the observer to a new host if the original host machine cannot be repaired in a timely fashion. To move the observer, you must stop allowing the first observer to observe this broker configuration, and then start a new observer on another host.

  1. Issue the DGMGRL STOP OBSERVER command to sever the link between the original observer and the broker configuration:

    DGMGRL> STOP OBSERVER;
    Done.
    
  2. Issue the DGMGRL SHOW CONFIGURATION VERBOSE command to verify that the configuration is no longer being observed:

    DGMGRL> SHOW CONFIGURATION VERBOSE;
     
    Configuration - DRSolution
     
      Protection Mode: MaxAvailability
      Databases:
        North_Sales - Primary database
        Warning: ORA-16819: fast-start failover observer not started
     
        South_Sales - (*) Physical standby database
        Warning: ORA-16819: fast-start failover observer not started
     
    (*) Fast-Start Failover target
     
    Properties:
      FastStartFailoverThreshold = '30'
      OperationTimeout = '30'
      TraceLevel = 'USER'
      FastStartFailoverLagLimit = '30'
      CommunicationTimeout = '180'
      ObserverReconnect = '0'
      FastStartFailoverAutoReinstate = 'TRUE'
      FastStartFailoverPmyShutdown = 'TRUE'
      BystandersFollowRoleChange = 'ALL'
      ObserverOverride = 'FALSE'
     
    Fast-Start Failover: ENABLED
     
      Threshold: 30 seconds
      Target: South_Sales
      Observer: observer.example.com
      Lag Limit: 30 seconds (not in use)
      Shutdown Primary: TRUE
      Auto-reinstate: TRUE
      Observer Reconnect: (none)
      Observer Override: FALSE
     
    Configuration Status:
    WARNING
    
  3. Note that you do not need to issue the DGMGRL SHOW CONFIGURATION command to verify that the observer has actually stopped. Successful completion of the DGMGRL STOP OBSERVER command will allow a new observer to become associated with the configuration.

9.5.3 Capturing Observer Actions in the Observer Log File

You can use the DGMGRL -logfile option to start the observer, so that all of the troubleshooting actions performed in Section 9.5.1 can be captured in a file. For example:

% dgmgrl -logfile observer.log / "start observer"

All the observer output is then recorded in a file named observer.log in the current working directory where you issued the DGMGRL command. If the specified log file is not accessible, then the observer output is sent to standard output as though a log file had not been specified.

Note that this is not only useful for troubleshooting problems with the observer, but also for troubleshooting problems with fast-start failover in general.