Let the Data Guard Broker control LOG_ARCHIVE_* parameters!

Let the Data Guard Broker control LOG_ARCHIVE_* parameters!

When using the Data Guard Broker, you don’t need to set any LOG_ARCHIVE_* parameter for the databases that are part of your Data Guard configuration. The broker is doing that for you. Forget about what you may have heard about VALID_FOR – you don’t need that with the broker. Actually, setting any of the LOG_ARCHIVE_* parameters with an enabled broker configuration might even confuse the broker and lead to warning or error messages. Let’s look at a typical example about the redo log transport mode. There is a broker configuration enabled with one primary database prima and one physical standby physt. The broker config files are mirrored on each site and spfiles are in use that the broker (the DMON background process, to be precise) can access:

When connecting to the broker, you should always connect to a DMON running on the primary site. The only exception from this rule is when you want to do a failover: That must be done connected to the standby site. I will now change the redo log transport mode to sync for the standby database. It helps when you think of the log transport mode as an attribute (respectively a property) of a certain database in your configuration, because that is how the broker sees it also.

[oracle@uhesse1 ~]$ dgmgrl sys/oracle@prima
DGMGRL for Linux: Version 11.2.0.3.0 - 64bit Production

Copyright (c) 2000, 2009, Oracle. All rights reserved.

Welcome to DGMGRL, type "help" for information.
Connected.
DGMGRL> edit database physt set property logxptmode=sync;
Property "logxptmode" updated

In this case, physt is a standby database that is receiving redo from primary database prima, which is why the LOG_ARCHIVE_DEST_2 parameter of that primary was changed accordingly:

[oracle@uhesse1 ~]$ sqlplus sys/oracle@prima as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Tue Sep 30 17:21:41 2014

Copyright (c) 1982, 2011, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options

SQL> show parameter log_archive_dest_2

NAME         TYPE  VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_2       string  service="physt", LGWR SYNC AFF
       IRM delay=0 optional compressi
       on=disable max_failure=0 max_c
       onnections=1 reopen=300 db_uni
       que_name="physt" net_timeout=3
       0, valid_for=(all_logfiles,pri
       mary_role)

The mirrored broker configuration files on all involved database servers contain that logxptmode property now. There is no new entry in the spfile of physt required. The present configuration allows now to raise the protection mode:

DGMGRL> edit configuration set protection mode as maxavailability;
Succeeded.

The next broker command is done to support a switchover later on while keeping the higher protection mode:

DGMGRL> edit database prima set property logxptmode=sync;
Property "logxptmode" updated

Notice that this doesn’t lead to any spfile entry; only the broker config files store that new property. In case of a switchover, prima will then receive redo with sync.

Now let’s do that switchover and see how the broker ensures automatically that the new primary physt will ship redo to prima:

DGMGRL> show configuration;

Configuration - myconf

  Protection Mode: MaxAvailability
  Databases:
    prima - Primary database
    physt - Physical standby database

Fast-Start Failover: DISABLED

Configuration Status:
SUCCESS

DGMGRL> switchover to physt;
Performing switchover NOW, please wait...
New primary database "physt" is opening...
Operation requires shutdown of instance "prima" on database "prima"
Shutting down instance "prima"...
ORACLE instance shut down.
Operation requires startup of instance "prima" on database "prima"
Starting instance "prima"...
ORACLE instance started.
Database mounted.
Switchover succeeded, new primary is "physt"

All I did was the switchover command, and without me specifying any LOG_ARCHIVE* parameter, the broker did it all like this picture shows:

Especially, now the spfile of the physt database got the new entry:

[oracle@uhesse2 ~]$ sqlplus sys/oracle@physt as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Tue Oct 14 15:43:41 2014

Copyright (c) 1982, 2011, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options

SQL> show parameter log_archive_dest_2

NAME         TYPE  VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_2       string  service="prima", LGWR SYNC AFF
       IRM delay=0 optional compressi
       on=disable max_failure=0 max_c
       onnections=1 reopen=300 db_uni
       que_name="prima" net_timeout=3
       0, valid_for=(all_logfiles,pri
       mary_role)

Not only is it not necessary to specify any of the LOG_ARCHIVE* parameters, it is actually a bad idea to do so. The guideline here is: Let the broker control them! Else it will at least complain about it with warning messages. So as an example what you should not do:

[oracle@uhesse1 ~]$ sqlplus sys/oracle@prima as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Tue Oct 14 15:57:11 2014

Copyright (c) 1982, 2011, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options

SQL> alter system set log_archive_trace=4096;

System altered.

Although that is the correct syntax, the broker now gets confused, because that parameter setting is not in line with what is in the broker config files. Accordingly that triggers a warning:

DGMGRL> show configuration;

Configuration - myconf

  Protection Mode: MaxAvailability
  Databases:
    physt - Primary database
    prima - Physical standby database
      Warning: ORA-16792: configurable property value is inconsistent with database setting

Fast-Start Failover: DISABLED

Configuration Status:
WARNING

DGMGRL> show database prima statusreport;
STATUS REPORT
       INSTANCE_NAME   SEVERITY ERROR_TEXT
               prima    WARNING ORA-16714: the value of property LogArchiveTrace is inconsistent with the database setting

In order to resolve that inconsistency, I will do it also with a broker command – which is what I should have done instead of the alter system command in the first place:

DGMGRL> edit database prima set property LogArchiveTrace=4096;
Property "logarchivetrace" updated
DGMGRL> show configuration;

Configuration - myconf

  Protection Mode: MaxAvailability
  Databases:
    physt - Primary database
    prima - Physical standby database

Fast-Start Failover: DISABLED

Configuration Status:
SUCCESS

Thanks to a question from Noons (I really appreciate comments!), let me add the complete list of initialization parameters that the broker is supposed to control. Most but not all is LOG_ARCHIVE*

LOG_ARCHIVE_DEST_n
LOG_ARCHIVE_DEST_STATE_n
ARCHIVE_LAG_TARGET
DB_FILE_NAME_CONVERT
LOG_ARCHIVE_FORMAT
LOG_ARCHIVE_MAX_PROCESSES
LOG_ARCHIVE_MIN_SUCCEED_DEST
LOG_ARCHIVE_TRACE
LOG_FILE_NAME_CONVERT
STANDBY_FILE_MANAGEMENT