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This post provides help troubleshooting a standby database (dataguard). This article covers the following problems:

• Troubleshooting Log transport services
• Troubleshooting Redo Apply services
• Troubleshooting SQL Apply services
• Common Problems
• Log File Destination Failures
• Handling Logical Standby Database Failures
• Problems Switching Over to a Standby Database
• What to Do If SQL Apply Stops
• Troubleshooting a Logical Standby Database

These SQL commands are compatible Oracle 18c, 12c, 11g and 10g.

Determine if archive logs of your DG environment are successfully being transferred to the standby

Run the following query:

select dest_id,status,error from v$archive_dest
where target=’STANDBY’;

If all remote destinations have a status of VALID then proceed to next step.
Else proceed to Troubleshooting Log Transport Services.

How many archives need to be transfered from Primary?

Connected on primary:

select thread#, min(sequence#), min(min_date), count(*) from (
select thread#, sequence#, count(*), max(first_time) min_date
from v$archived_log
where first_time > sysdate – 2
group by thread#, sequence#
having count(*) <2
order by 1,2
)
group by thread#;

Determine if the standby is a Physical standby or a Logical Standby

To determine the standby type run the following query on the standby:

select database_role from v$database;

If the standby is a physical standby then proceed to Troubleshooting Redo
Apply. Else proceed to Troubleshooting Logical Apply.

Troubleshooting Log transport services

Verify that the primary database is in archive log mode and has automatic archiving enabled

select log_mode from v$database;

or in SQL*Plus

archive log list 

Verify that sufficient space exist in all archive destinations

The following query can be used to determine all local and mandatory destinations that need to be checked:

select dest_id,destination from v$archive_dest
where schedule=’ACTIVE’
and (binding=’MANDATORY’ or target=’PRIMARY’);

Determine if the last log switch to any remote destinations resulted in an
error

select dest_id,status,error from v$archive_dest
where target=’STANDBY’;

Address any errors that are returned in the error column. Perform a log
switch and re-query to determine if the issue has been resolved.

Determine if any error conditions have been reached

Query the v$dataguard_status view:

select message, to_char(timestamp,’HH:MI:SS’) timestamp
from v$dataguard_status
where severity in (‘Error’,’Fatal’)
order by timestamp

Gather information about how the remote destinations are performing the
archival

select dest_id,archiver,transmit_mode,affirm,net_timeout,delay_mins,async_blocs
from v$archive_dest where target=’STANDBY’

Determine the current sequence number, the last sequence archived, and the last sequence applied to a standby

Perhaps, the most important query to troubleshoot a stsandby configuration:

select ads.dest_id,
max(sequence#) “Current Sequence”,
max(log_sequence) “Last Archived”,
max(applied_seq#) “Last Sequence Applied”
from v$archived_log al, v$archive_dest ad, v$archive_dest_status ads
where ad.dest_id=al.dest_id
and al.dest_id=ads.dest_id
group by ads.dest_id

If you are remotely archiving using the LGWR process then the archived
sequence should be one higher than the current sequence. If remotely
archiving using the ARCH process then the archived sequence should be equal to the current sequence. The applied sequence information is updated at
log switch time.

Troubleshooting Redo Apply services

Verify that the last sequence# received and the last sequence# applied to
standby database

select max(al.sequence#) “Last Seq Recieved”,
max(lh.sequence#) “Last Seq Applied”
from v$archived_log al, v$log_history lh

If the two numbers are the same then the standby has applied all redo sent
by the primary. If the numbers differ by more than 1 then proceed to next step.

Verify that the standby is in the mounted state

select open_mode from v$database;

Determine if there is an archive gap on your physical standby database

By querying the V$ARCHIVE_GAP view as shown in the following query:

select * from v$archive_gap;

The V$ARCHIVE_GAP fixed view on a physical standby database only returns the next gap that is currently blocking redo apply from continuing.

After resolving the identified gap and starting redo apply, query the
V$ARCHIVE_GAP fixed view again on the physical standby database to
determine the next gap sequence, if there is one. Repeat this process
until there are no more gaps.

If v$archive_gap view does’nt exists:

WITH prod as (select max(sequence#) as seq from v_$archived_log where RESETLOGS_TIME = (select RESETLOGS_TIME from v_$database)), stby as (select max(sequence#) as seq,dest_id dest_id from v_$archived_log where first_change# > (select resetlogs_change# from v_$database) and applied = ‘YES’ and dest_id in (1,2) group by dest_id) select prod.seq-stby.seq,stby.dest_id from prod, stby

Verify that managed recovery is running

select process,status from v$managed_standby;

When managed recovery is running you will see an MRP process. If you do not see an MRP process then start managed recovery by issuing the following command:

recover managed standby database disconnect;

Some possible statuses for the MRP are listed below:

ERROR – This means that the process has failed. See the alert log or v$dataguard_status for further information.

WAIT_FOR_LOG – Process is waiting for the archived redo log to be completed. Switch an archive log on the primary and query v$managed_standby to see if the status changes to APPLYING_LOG.

WAIT_FOR_GAP – Process is waiting for the archive gap to be resolved. Review the alert log to see if FAL_SERVER has been called to resolve the gap.

APPLYING_LOG – Process is applying the archived redo log to the standby database.à

Troubleshooting SQL Apply services

Verify that log apply services on the standby are currently running.

To verify that logical apply is currently available to apply changes perform the following query:

SELECT PID, TYPE, STATUS, HIGH_SCN  FROM V$LOGSTDBY;

When querying the V$LOGSTDBY view, pay special attention to the HIGH_SCN column. This is an activity indicator. As long as it is changing each time you query the V$LOGSTDBY view, progress is being made. The STATUS column gives a text description of the current activity.

If the query against V$LOGSTDBY returns no rows then logical apply is not running. Start logical apply by issuing the following statement:

SQL> alter database start logical standby apply;

If the query against V$LOGSTDBY continues to return no rows then proceed to  next step.

Determine if there is an archive gap in your dataguard configuration

Query the DBA_LOGSTDBY_LOG view on the logical standby database.

SELECT SUBSTR(FILE_NAME,1,25) FILE_NAME, SUBSTR(SEQUENCE#,1,4) “SEQ#”, FIRST_CHANGE#, NEXT_CHANGE#, TO_CHAR(TIMESTAMP, ‘HH:MI:SS’) TIMESTAMP, DICT_BEGIN BEG, DICT_END END, SUBSTR(THREAD#,1,4) “THR#” FROM DBA_LOGSTDBY_LOG ORDER BY SEQUENCE#;

Copy the missing logs to the logical standby system and register them using the ALTER DATABASE REGISTER LOGICAL LOGFILE statement on your logical standby database. For example:

SQL> ALTER DATABASE REGISTER LOGICAL LOGFILE ‘/u01/oradata/arch/myarc_57.arc’;

After you register these logs on the logical standby database, you can restart log apply services. The DBA_LOGSTDBY_LOG view on a logical standby database only returns the next gap that is currently blocking SQL apply operations from continuing.

After resolving the identified gap and starting log apply services, query the DBA_LOGSTDBY_LOG view again on the logical standby database to determine the next gap sequence, if there is one. Repeat this process until there are no more gaps.

Verify iflogical apply is receiving errors while performing apply operations.

Log apply services cannot apply unsupported DML statements, DDL statements and Oracle supplied packages to a logical standby database in SQL apply mode. When an unsupported statement or package is encountered, SQL apply operations stop. To determine if SQL apply has stopped due to errors you should query the DBA_LOGSTDBY_EVENTS view. When querying the view, select the columns in order by EVENT_TIME. This ordering ensures that a shutdown
failure appears last in the view. For example:

SQL> SELECT XIDUSN, XIDSLT, XIDSQN, STATUS, STATUS_CODE
FROM DBA_LOGSTDBY_EVENTS
WHERE EVENT_TIME =
(SELECT MAX(EVENT_TIME) FROM DBA_LOGSTDBY_EVENTS);

If an error requiring database management occurred (such as adding a tablespace, datafile, or running out of space in a tablespace), then you can fix the problem manually and resume SQL apply.

If an error occurred because a SQL statement was entered incorrectly, conflicted with an existing object, or violated a constraint then enter the correct SQL statement and use the DBMS_LOGSTDBY.SKIP_TRANSACTION procedure to ensure that the incorrect statement is ignored the next time SQL apply operations are run.

Query DBA_LOGSTDBY_PROGRESS to verify that log apply services is progressing

The DBA_LOGSTDBY_PROGRESS view describes the progress of SQL apply operations on the logical standby databases. For example:

SQL> SELECT APPLIED_SCN, APPLIED_TIME, READ_SCN, READ_TIME,
NEWEST_SCN, NEWEST_TIME
FROM DBA_LOGSTDBY_PROGRESS;

The APPLIED_SCN indicates that committed transactions at or below that SCN have been applied. The NEWEST_SCN is the maximum SCN to which data could be applied if no more logs were received. This is usually the MAX(NEXT_CHANGE#)-1
from DBA_LOGSTDBY_LOG when there are no gaps in the list. When the value of NEWEST_SCN and APPLIED_SCN are the equal then all available changes have been applied. If you APPLIED_SCN is below NEWEST_SCN and is increasing then
SQL apply is currently processing changes.

Verify that the table that is not receiving rows is not listed in the DBA_LOGSTDBY_UNSUPPORTED.

The DBA_LOGSTDBY_USUPPORTED view lists all of the tables that contain datatypes not supported by logical standby databases in the current release. These tables are not maintained (will not have DML applied) by the logical
standby database. Query this view on the primary database to ensure that those tables necessary for critical applications are not in this list. If the primary database includes unsupported tables that are critical, consider using a physical standby database.

Author: Oracle Corporation modified by Vincent Fenoll

I want to start or stop redo apply without dgbroker. I also want to know other queries to check Dataguard and standby status.
These commands are compatible with Oracle 18c, 12c, 11g, 10g, 9i.

Starting Redo Apply on standby database

 

To start Redo Apply in the foreground, issue the following SQL statement.

Without Real Time Apply (RTA) on standby database

ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION;

 

With Real Time Apply (RTA)

ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE DISCONNECT;

 

Stopping Redo Apply on standby database

To stop Redo Apply in the foreground, issue the following SQL statement.

ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;

 

Monitoring Redo Apply on Physical Standby Databases

 

Last sequence received and applied

SELECT ARCH.THREAD# "Thread", ARCH.SEQUENCE# "Last Sequence Received", APPL.SEQUENCE# "Last Sequence Applied", (ARCH.SEQUENCE# - APPL.SEQUENCE#) "Difference"
FROM
(SELECT THREAD# ,SEQUENCE# FROM V$ARCHIVED_LOG WHERE (THREAD#,FIRST_TIME ) IN (SELECT THREAD#,MAX(FIRST_TIME) FROM V$ARCHIVED_LOG GROUP BY THREAD#)) ARCH,
(SELECT THREAD# ,SEQUENCE# FROM V$LOG_HISTORY WHERE (THREAD#,FIRST_TIME ) IN (SELECT THREAD#,MAX(FIRST_TIME) FROM V$LOG_HISTORY GROUP BY THREAD#)) APPL
WHERE
ARCH.THREAD# = APPL.THREAD#;

 

Standby database process status

select distinct process, status, thread#, sequence#, block#, blocks from v$managed_standby ;

 

If using real time apply

select TYPE, ITEM, to_char(TIMESTAMP, 'DD-MON-YYYY HH24:MI:SS') from v$recovery_progress where ITEM='Last Applied Redo';

or,

select recovery_mode from v$archive_dest_status where dest_id=1;

 

Author: Vincent Fenoll (Oracle DBA in Montreal)

Activation of dgbroker in a Oracle 12.2 configuration

- Primary RAC 2 nodes:
servers: PRIMARY-HOST-NODE1 and PRIMARY-HOST-NODE2
database: PRIMARY-DB-UNIQ-NAME1 and PRIMARY-DB-UNIQ-NAME2
- Standby: RAC 1 node
server: STANDBY-HOST-NODE1
database: STANDBY-DB-UNIQ-NAME1 (here SID has the same name as primary)

Pre-requisites for the dgbroker configuration

Network configuration

Prepare a dedicated local listener on each node

All Data Guard Broker configurations must have a specific static listener entry configured in the local listener of each instance in the Data Guard configuration for the Primary database and all standby databases. A static entry is needed for the Broker to be able to connect remotely to a database that has been shut down by the Broker during certain operations.

listener.ora
Example for node PRIMARY-HOST-NODE1. Has also to be done for PRIMARY-HOST-NODE2 and STANDBY-HOST-NODE1.

LISTENERDG =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = PRIMARY-HOST-NODE1)(PORT = 1522))
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1522))
)
)

SID_LIST_LISTENERDG =
(SID_LIST =
(SID_DESC =
(GLOBAL_DBNAME = PRIMARY-DB-UNIQ-NAME1)
(ORACLE_HOME = /u01/app/oracle/product/12.2.0/dbhome_1)
(SID_NAME = PRIMARY-DB-UNIQ-NAME1)
)
(SID_DESC =
(GLOBAL_DBNAME = PRIMARY-DB-UNIQ-NAME_DGB)
(ORACLE_HOME = /u01/app/oracle/product/12.2.0/dbhome_1)
(SID_NAME = PRIMARY-DB-UNIQ-NAME1)
)
)

USE_SID_AS_SERVICE_listenerDG=ON
ADR_BASE_LISTENERDG = /u01/app/oracle

Add alias in the tnsnames.ora

On each node (2 primary/ 1standby) we create an alias on the dedicated listener LISTENERDG (1522 port).

 

Primary nodes

 

# Primary alias(for node 2, modify for PRIMARY-HOST-NODE2 and PRIMARY-DB-UNIQ-NAME2
PRIMARY-DB-UNIQ-NAME =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = PRIMARY-HOST-NODE1)(PORT = 1522))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = PRIMARY-DB-UNIQ-NAME1)
(INSTANCE_NAME = PRIMARY-DB-UNIQ-NAME1)
)
)

# Standby alias STANDBY-DB-UNIQ-NAME1
STANDBY-DB-UNIQ-NAME1 =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = STANDBY-HOST-NODE1)(PORT = 1522))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SID =PRIMARY-DB-UNIQ-NAME1)
)
)

Standby node

# Primary alias (use of: scan host and PRIMARY-DB-UNIQ-NAME_DGB service)

PRIMARY-DB-UNIQ-NAME =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = PRIMARY-SCAN)(PORT = 1522))
(CONNECT_DATA =
(SERVICE_NAME =PRIMARY-DB-UNIQ-NAME_DGB)
)
)

# Standby alias
STANDBY-DB-UNIQ-NAME1 =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = STANDBY-HOST-NODE1)(PORT = 1522))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SID =PRIMARY-DB-UNIQ-NAME1)
)
)

Database configuration parameters

Dgbroker config files

On the Primary host

Create DGBROKER directory on ASM: +DATA/PRIMARY-DB-UNIQ-NAME/DGBROKER
Set dg_broker_config_file1 and dg_broker_config_file2:

alter system set dg_broker_config_file1 = '+DATA/PRIMARY-DB-UNIQ-NAME/DGBROKER/dr1PRIMARY-DB-UNIQ-NAME.dat' scope=both sid='*';
alter system set dg_broker_config_file2 = '+DATA/PRIMARY-DB-UNIQ-NAME/DGBROKER/dr2PRIMARY-DB-UNIQ-NAME.dat' scope=both sid='*';

(dg_broker_start parameter has to be=false before modifying dg_broker_config_file)

On the standby

Create DGBROKER directory on ASM: +DATA/STANDBY-DB-UNIQ-NAME1 /DGBROKER

alter system set dg_broker_config_file1 = '+DATA/STANDBY-DB-UNIQ-NAME1/DGBROKER/dr1PRIMARY-DB-UNIQ-NAME.dat' scope=both sid='*';
alter system set dg_broker_config_file2 = '+DATA/STANDBY-DB-UNIQ-NAME1/DGBROKER/dr2PRIMARY-DB-UNIQ-NAME.dat' scope=both sid='*';

 

Change of 2 parameters

On primary and standby:

alter system set dg_broker_start=true scope=both sid='*';
alter system set LOG_ARCHIVE_DEST_2='' scope=both sid='*';

 

Dataguard configuration

On primary or standby;
dgmgrl (in the database Oracle_home)

connect /
— Optional: in case a configuration already exists, we drop it.
disable database STANDBY-DB-UNIQ-NAME1
remove configuration;

-- Configuration creation
CREATE CONFIGURATION dgb_prod AS PRIMARY DATABASE IS PRIMARY-DB-UNIQ-NAME CONNECT IDENTIFIER IS PRIMARY-DB-UNIQ-NAME;

-- Add 1 standby db
ADD DATABASE STANDBY-DB-UNIQ-NAME1 AS CONNECT IDENTIFIER IS STANDBY-DB-UNIQ-NAME1 MAINTAINED AS PHYSICAL;

-- Enable
enable configuration;

-- see config
show configuration
(Result:)
Configuration - dgb_prod
Protection Mode: MaxPerformance
Members:
PRIMARY-DB-UNIQ-NAME - Primary database
STANDBY-DB-UNIQ-NAME1 - Physical standby database
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS (status updated 36 seconds ago)

 

Verification of the configuration

show configuration

show database verbose STANDBY-DB-UNIQ-NAME1

validate database ‘STANDBY-DB-UNIQ-NAME1’

validate database ‘PRIMARY-DB-UNIQ-NAME’

 

Switchover

— Always connect with password for switchover/Failover
connect sys/my-sys-password@PRIMARY-DB-UNIQ-NAME

switchover to STANDBY-DB-UNIQ-NAME1

show configuration verbose

— Return to primary
connect sys/my-sys-password@PRIMARY-DB-UNIQ-NAME

switchover to STANDBY-DB-UNIQ-NAME1 PRIMARY-DB-UNIQ-NAME

show configuration verbose

 

Failover

FAILOVER TO STANDBY-DB-UNIQ-NAME1

— If flashback enabled, the original primary database can now be configured as a standby.
REINSTATE DATABASE PRIMARY-DB-UNIQ-NAME

 

Snapshot Standby

— If flashback database is enabled on primary (not mandatory for standby)
dgmgrl
connect sys/my-sys-password@PRIMARY-DB-UNIQ-NAME
CONVERT DATABASE cdb1_stby TO SNAPSHOT STANDBY;
[Work read/write on STANDBY-DB-UNIQ-NAME1]
— When finished working, convert it back to a standby database
CONVERT DATABASE cdb1_stby TO PHYSICAL STANDBY;

 

Disable/Enable the log transport on the primary

OFF

dgmgrl /
DGMGRL> edit database ‘cbuerpp’ set state=TRANSPORT-OFF;
DGMGRL> show database verbose ‘cbuerpp’
Database – cbuerpp
Role: PRIMARY
Intended State: TRANSPORT-OFF
Instance(s):
…..

If we look at the db parameter:
SQL> show parameter log_archive_dest_state_2

NAME TYPE VALUE
———————————— ———– ——————————
log_archive_dest_state_2 string RESET

 

ON

DGMGRL> edit database ‘cbuerpp’ set state=TRANSPORT-ON;

 

Disable/Enable the log apply in the standby database

APPLY-OFF

EDIT DATABASE ‘cbuerps’ SET STATE=’APPLY-OFF’;

APPLY-ON

EDIT DATABASE ‘cbuerps’ SET STATE=’APPLY-ON’;

 

Other commands

— Change Protection mode
EDIT CONFIGURATION SET PROTECTION MODE AS MaxAvailability;

— Change property of a member (see properties with “show database verbose STANDBY-DB-UNIQ-NAME1”)
edit database STANDBY-DB-UNIQ-NAME1 set property LogXptMode=’SYNC’;
edit database STANDBY-DB-UNIQ-NAME1 set property StandbyFileManagement=’AUTO’;

— Change a parameter (e.g. database verbose)
EDIT DATABASE ‘STNDBY’ SET PROPERTY ‘Enterprise Manager Name’ = ‘STNDBY.MY_DB_DOMAIN’;

EDIT DATABASE ‘MYDB’ SET PROPERTY ‘Enterprise Manager Name’ = ‘MYDB.MY_DB_DOMAIN’;

 

Author: Vincent Fenoll – Oracle DBA Montréal