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Thread: Troubleshooting Data Guard Implementation II

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    Expert Oracle Administrator
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    Troubleshooting Data Guard Implementation II

    Physical Standby Issues
    You will likely encounter several common issues when managing a physical database:
    ■ You cannot mount the physical standby database.
    ■ The standby archive destination is not defined properly.
    ■ The standby site does not receive logs.
    ■ The standby site is not processing the logs (MRP down, and so on).

    Unable to Mount the Physical Standby Database
    The physical standby can’t be mounted if the control file was created with an operating system–
    created backup or a backup created using an ALTER DATABASE statement without the STANDBY
    options. The standby control file must be created with the ALTER DATABASE CREATE STANDBY
    CONTROLFILE statement or the RMAN BACKUP CURRENT CONTROLFILE with the FOR STANDBY
    option.

    Primary Database Shutdown
    If you have configured standby redo log files on your standby database, the size of the current
    standby redo log file on each standby database must be the same size as the redo log file on the
    primary database. After a log switch, if no available standby redo log files match the size of the redo
    log file on the primary database, the primary will shut down if it is in Maximum Protection mode.
    The primary database becomes unsynchronized if it is in Maximum Availability mode. You will
    see the following message in the alert log:
    No standby log files of size <#> blocks available.

    ORA-16066
    You will encounter this error when the REMOTE_ARCHIVE_ENABLE parameter is set to FALSE.
    This parameter controls whether the archival of the redo logs to remote destinations is permitted.

    ORA-16204: Parameter %s Cannot Be Parsed
    The value for the LOG_ARCHIVE_DEST_n parameter is incorrect.
    Remote Archival to Standby Database Fails with an ORA-01031
    You will see this error if an archiver process (ARCn) or LogWriter Network Service (LNS) process
    at the primary database fails with the ORA-01031 and the redo is not getting transferred to the
    standby. This is a result of a missing password file on the standby database. Copy the password
    file from the primary to the standby database, and restart the standby database.

    Standby Database Cannot Apply Redo
    If you encounter issues with applying the logs to the standby database, and you see the ORA-
    00326 message in your alert log, you’ll see the following:
    ORA-00326: log begins at change <SCN> , need earlier change <SCN>
    This means that media recovery has found an archive log which was generated after the required
    archive log. It needs the correct log. When you are using Data Guard Redo Apply, this error cannot
    occur since the managed recovery process (MRP) will provide media recovery only with the logs in
    the correct order. If the next log is not in the correct order, the MRP will not pass anything to media
    recovery. This usually occurs when Data Guard ends up performing gap resolution.
    If you were using manual recovery and feeding media recovery archive logs one at a time, it
    normally means that you provided an archive log generated after the required log. You can
    remedy the problem by providing the correct file.

    Log Shipment Errors—ORA-12570
    You may encounter sporadic “ORA-12570: TNS packet reader failure” messages when shipping
    redo data between the primary and standby when the connection is going through a firewall. If
    you can’t disable the firewall timeout or bypass the firewall, set sqlnet.expire_time in the
    sqlnet.ora file on both servers.

    Logical Standby Database Failures
    Several issues can occur with a logical standby environment:
    ■ SQL Apply stops.
    ■ SQL Apply hangs.
    ■ SQL Apply cannot keep up with the primary.
    ■ Data is not applied to the logical standby.

    What to Do if SQL Apply Stops
    Log apply services cannot apply unsupported Data Manipulation Language (DML) statements,
    Data Definition Language (DDL) statements, and Oracle-supplied packages to a logical standby
    database running SQL Apply. The following sections summarize some of the conditions under
    which SQL Apply will stop.

    Determine What Has Failed You can find the last statement that SQL Apply tried to process in
    the DBA_LOGSTDBY_EVENTS view:
    SQL> SELECT XIDUSN, XIDSLT, XIDSQN, STATUS, STATUS_CODE
    2 FROM DBA_LOGSTDBY_EVENTS
    3 WHERE EVENT_TIME =
    4(SELECT MAX(EVENT_TIME)
    5 FROM DBA_LOGSTDBY_EVENTS);
    The output of the query will reveal the statement and error that caused SQL Apply to fail.

    ORA-01403: No Data Found You will encounter the ORA-01403 error when DML is executed
    on the logical standby to tables maintained by SQL Apply. This will generally occur if someone
    makes these changes with SYSDBA privileges or if the logical standby guard was disabled. The
    primary and the logical can get out of sync and the error won’t show up until the table on the
    primary standby is updated.
    To resolve the issue, you would need to skip and re-instantiate the table. Make sure that
    you have a database link defined to connect to the primary database. You can use the dbms_
    logstdby.skip and dbms_logstdby.instantiate_table procedures to accomplish this,
    as demonstrated here:
    SQL> EXEC DBMS_LOGSTDBY.SKIP('DML','ACTORS','%');
    SQL> EXECUTE DBMS_LOGSTDBY.INSTANTIATE_TABLE
    2 ('MATRIX_USER', 'ACTORS', 'MATRIX_DBLINK');

    ORA-16211: Unsupported Record Found in the Archived Redo Log You will encounter the
    ORA-16211 error when log apply encounters a record in the archived redo log that could not be
    interpreted. This error could occur under any number of circumstances; however, a few
    documented potential causes for this error do exist:
    ■ Nologging on an object on the primary
    ■ Changes made to an Indexed Organized Table (IOT) on the primary
    ■ Direct path inserts on a partition table
    To resolve this error, you can re-instantiate the object or drop the object. In either case, you
    will want to determine the archive log with the error and send it to Oracle support for analysis.

    Handling DDL Issues You will often face issues with DDL statements in a standby database.
    For example, a DBA may add a datafile to the primary and the path is not valid on the logical
    standby. Remember that the DB_FILE_NAME_CONVERT parameters are not used on a logical
    standby. Keep in mind that the following statements are skipped automatically on the standby:
    CREATE and ALTER DATABASE commands
    CREATE and DROP DATABASE LINK commands
    The following procedures can be used to help resolve issues with DDL:
    DBMS_LOGSTDBY.SKIP Skips a schema or object or a type of statement
    DBMS_LOGSTDBY.SKIP_ERROR Ignores a class of errors and continues the SQL Apply
    DBMS_LOGSTDBY.SKIP_TRANSACTION Skips a failed transaction provided that you
    issued a compensating transaction

    SQL Apply Hanging
    If it appears that SQL Apply is hanging, perform the following steps for investigative procedures:

    1. Check DBA_LOGSTDBY_PROGRESS to see if any activity is occurring:
    SQL> SELECT APPLIED_SCN, APPLIED_TIME, READ_SCN,
    READ_TIME, NEWEST_SCN, NEWEST_TIME
    FROM DBA_LOGSTDBY_PROGRESS;

    2. Check the HIGH_SCN from the V$LOGSTDBY view. The SCN should change as the SQL
    Apply progresses:
    SQL> SELECT TYPE, HIGH_SCN, STATUS
    FROM V$LOGSTDBY;

    3. Check V$LOGSTDBY_STATS for information on the activity on the standby. You can
    look at the number of transactions applied or transactions ready and tell whether the
    transactions are being applied as fast as they are being read
    Last edited by Hemant; 01-10-2012 at 07:48 PM.

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