【DATAGUARD】Oracle Dataguard物理備庫切換最佳實踐(sqlplus)

備查 （ 11.2 Data Guard Physical Standby Switchover Best Practices using SQL*Plus (Doc ID 1304939.1)）

In this Document

APPLIES TO:

Oracle Database Cloud Service - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Backup Service - Version N/A and later
Oracle Database - Enterprise Edition - Version 11.2.0.1 and later
Oracle Database Cloud Schema Service - Version N/A and later
Information in this document applies to any platform.

GOAL

Perform trouble free Data Guard switchover.

Note: for Data Guard switchover using the Broker please refer to Note  1305019.1 - "11.2 Data Guard Physical Standby Switchover Best Practices using the Broker"

SOLUTION

For the purposes of this document, the following fictitious environment is used as an example to describe the procedure:

Primary Database:
DB_NAME: SFO

Standby Database:
DB_UNIQUE_NAME: NYC

**************

I. Prerequisites / Preparation

Apply Latest Patch Bundle.

• Review Note 785351.1 "11gR2 Upgrade Companion"
• Make sure to check the “Patches Recommended” tab.
• See Note 756671.1 for the latest available patches or patchset updates.

Review Primary Database Initialization Parameters

Further ensure 'compatible' is set correctly and to the same Value on the Primary and Standby Site.

Verify the Setup

Understand and Test Fallback Options

II. Pre-Switchover Checks

These steps should be completed before the switchover planned maintenance window begins. Our recommendation is that these are done a couple days in advance.

Verify Managed Recovery is running on the standby

The following query at the standby verifies that managed recovery is running:

The following query at the Primary verifies that recovery is running with “REAL TIME APPLY” option. In the example below, LOG_ARCHIVE_DEST_2 is established to ship redo to the target standby (dest_id=2):

If managed standby recovery is not running or not started with real-time apply, restart managed recovery with real-time apply enabled:

Note: If you previously defined a delay for this standby the delay is ignored when you start real time apply
For more information see 

Verify Sufficient Number of Archiver Processes

Ensure Online Redo Log Files on the Target Physical Standby have been cleared

Online redo logs on the target physical standby need to be cleared before that standby database can become a primary database. Although this will automatically happen as part of the SWITCHOVER TO PRIMARY command, it is recommended that the logs are cleared prior to the switchover. 

Setting the LOG_FILE_NAME_CONVERT parameter at the physical standby will cause the online redo logs to be automatically cleared when managed recovery is started on the standby. 

If your databases are using Oracle Managed Files (OMF) or you have already set the parameter LOG_FILE_NAME_CONVERT you can skip this step as the online log files will always be cleared automatically.

Clearing online redo logs as part of the SWITCHOVER TO PRIMARY command can make the switchover command susceptible to termination by another process that is waiting on access to the CONTROLFILE. The CONTROLFILE waiter will attempt to kill the switchover after a timeout is 15 minutes.

Oracle recommends setting LOG_FILE_NAME_CONVERT to automatically clear online redo logs on the physical standby database. In the event the primary database and the physical standby database have the exact same directory path to the online redo logs, it is acceptable to set LOG_FILE_NAME_CONVERT such that the entry pairs have the same value. 

As an example, if the online redo logs are stored in /oradata/order_db/redo for both the primary and physical standby databases on their respective servers, you can set the parameter value as

LOG_FILE_NAME_CONVERT=’/oradata/order_db/redo/’,’/oradata/order_db/redo/’

This will initiate automatic clearing of the online redo logs on the physical standby database when managed recovery is started.

Since the LOG_FILE_NAME_CONVERT parameter is not dynamic you must restart the standby database for the property change to take affect. 

If you have not set your environment to automatically clear the online redo logs and you do not want to restart the standby database, you should manually clear them at some point prior to the switchover. This can be done at any time.

On the target physical standby run the following query to determine if the online redo logs have not been cleared:

If the above query returns rows, on the target physical standby stop Redo Apply, issue the following statement for each GROUP# returned and restart Redo Apply:

Please note that later when you do the actual switchover if it is terminated by a CONTROLFILE waiter timeout, just re-issue the SWITCHOVER TO PRIMARY command until it completes successfully.

You should monitor your alert log to ensure your online redo logs are being cleared and you are not experiencing some other issue.

Verify there are no large Gaps

Identify the current sequence number for each thread on the primary database

Verify the target physical standby database has applied up to, but not including the logs from the primary query. On the standby the following query should be within 1 or 2 of the primary query result.

If large gaps exist (more than 3 logs) then see  .

Verify Primary and Standby tempfiles match and all datafiles are ONLINE

If the queries do not match then you can correct the mismatch now or immediately after the open of the new primary database.

Prior to switchover, on the target standby, verify that all datafiles necessary for updates after role transition to primary are ONLINE.

On the target standby:

If there are any OFFLINE datafiles, and these are needed after switchover, bring them ONLINE:

III. Switchover

These steps are completed as part of the switchover process on the day of the planned outage.

Cancel any apply delay for the target standby

Remove any delay in applying redo that may be in effect on the standby database that will become the new primary database. If there is a delay then on the target standby database execute the following command.

Clear Potential Blocking Parameters & Jobs

Capture current job state on the primary:

Depending on what the running job is, be ready to terminate the job if necessary.

Note: Job candidates to be disabled among others: oracle text sync and optimizer, RMAN backups, application garbage collectors, application background agents.

Block further job submission

Disable any jobs that may interfere.

Shutdown all mid-tiers (optional)

This can be done in parallel to the switchover.

Turn on Data Guard tracing on primary and standby

Tracing is turned on to have diagnostic information available in case any issues arise. Turning on tracing does not have any noticeable impact on switchover time but does require space for the trace output.

Capture the current value on both the primary and the target physical standby databases

Set Data Guard trace level to 8191 on both the primary and the target physical standby databases

Trace output will appear under the destination pointed to by the database parameter BACKGROUND_DUMP_DEST with “mrp” in the file name.

Tail Alert Logs (optional) on all instances

Locate alert logs by showing database parameter background_dump_dest

Tail the alert logs

> tail –f <background_dump_dest location>/alert*

Create Guaranteed Restore Points (optional)

The standard switchover fallback options should suffice for successfully backing out of a switchover. However, if you want an additional fallback option then you can create a guaranteed restore point on the primary and standby database participating in the switchover.

On the standby

Stop the apply process

Create a guaranteed restore point

Start the apply process

On the primary

Create a guaranteed restore point

Note: If a guaranteed restore points are created, make sure they are dropped post-switchover!

Verify that the primary database can be switched to the standby role

Query the SWITCHOVER_STATUS column of the V$DATABASE view on the primary database:

A value of TO STANDBY or SESSIONS ACTIVE (which requires the WITH SESSION SHUTDOWN clause on the switchover command) indicates that the primary database can be switched to the standby role. If neither of these values is returned, a switchover is not possible because redo transport is either mis-configured or is not functioning properly. See 

If The Primary is a RAC, then shutdown all secondary primary instances

A normal or immediate shutdown can be done, but to expedite the shutdown issue a SHUTDOWN ABORT on secondary RAC instances  on the primary cluster only leaving one Primary instance up. Wait until the remaining Primary instance has completed cluster reconfiguration (and performed recovery if you chose to abort the secondary instances) before continuing.

Switchover the primary to a standby database

If an ORA-16139 error is encountered, as long as V$DATABASE.DATABASE_ROLE=’PHYSICAL STANDBY’, then you can proceed. A common case where this can occur is when there are a large number of data files. Once managed recovery is started on the new standby, the database will recover.

If the role was not changed then you need to cancel the switchover and review the alert logs and trace files further.

Verify the standby has received the end-of-redo (EOR) log(s)

In the  primary alert log you will see messages like these:

And correspondingly in the  standby alert log file you should see messages like these:

In versions prior to Oracle Database 11g Release 2, the MRP (Redo Apply coordinator) would stop automatically after processing the End-of-Redo marker. With Oracle Database 11g Release 2, it no longer stops leaving all bystander standby databases still ready to apply redo from the new primary database without having to be restarted. The MRP process will be shut down automatically by the switchover command when executed at the target standby database.

Verify that the standby database can be switched to the primary role

Query the SWITCHOVER_STATUS column of the V$DATABASE view on the standby database:

A value of TO PRIMARY or SESSIONS ACTIVE indicates that the standby database is ready to be switched to the primary role. If neither of these values is returned, verify that redo apply is active and that redo transport is configured and working properly. Continue to query this column until the value returned is either TO PRIMARY or SESSIONS ACTIVE.

Switchover the standby database to a primary

In the standby alert log file you should see messages like these:

Open the new primary database

Note: There will be an increase in I/O activity while the new primary’s standby redo logs are cleared.

Correct any tempfile mismatch

If there was a tempfile that was not corrected during the pre-switchover check, then correct it now on the new primary.

Restart the new standby

If the new standby database (former primary database) was not shutdown since switching it to standby, bring it to the mount state and start managed recovery. This can be done in parallel to the new primary open.

Note: If you use IMMEDIATE, an ABORT will be performed anyway as of 11.2.0.2 and you would see the following in the alert log:

Performing implicit shutdown abort due to switchover to physical standby
Shutting down instance (abort)
License high water mark = 15
USER (ospid: 14665): terminating the instance
Instance terminated by USER, pid = 14665

Note: If you were using a delay for your standby then you would restart the apply without real time apply:

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT;

Finally, if the database is a RAC, then start all secondary instances on the new standby.

Contingency or Fallback

See   in the Data Guard Concepts and Administration manual.

IV. Post-Switchover Steps

Set Trace to Prior Value

For each instance on the Primary and Standby:

Reset Jobs

Set the job queue processes to its original value on the new standby.

Enable any jobs that were disabled.

Drop any Switchover Guaranteed Restore Points

On all databases where a Guaranteed Restore point was created