Configuration of Oracle 10g Data guard
Primary Database Requirements for Data Guard:FORCE LOGGING must be enabled:
SQL> select force_logging from v$database;
SQL> alter database force logging;
ARCHIVELOG mode and automatic archiving must be enabled:
SQL> archive log list
MAXLOGFILES >= (2 * Current Redo Log Groups) + 1:
SQL> select records_used “Current Groups”,records_total “Max Groups” from v$controlfile_record_section where type = ‘REDO LOG';
listener.ora Additions:Define the standby database SID on the standby site:
(SID_DESC=
(SID_NAME=PROD2)
(ORACLE_HOME=/pgms/oracle/product/v9204)
)
(in $ORACLE_HOME/network/admin/listener.ora)
tnsnames.ora Additions:Define the standby database connect string on the primary site:
myserver_prod2 =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS =(PROTOCOL = TCP) (Host = 123.45.67.89) — whatever host IP has PROD2(Port = 1521)
) )
(CONNECT_DATA = (SID = PROD2) ) )
(define myserver_prod and myserver_prod2 on both primary and standby sites for quick switchovers)
sqlnet.ora and /etc/oratab Additions:Enable dead connection detection on the primary and standby sites:
sqlnet.expire_time=2
(in $ORACLE_HOME/network/admin/sqlnet.ora)
Add the standby database’s entry to /etc/oratab on the standby site:
PROD2:/pgms/oracle/product/v9204:N
Standby Database Parameter File:Create the initPROD2.ora parameter file to be used for the standby database (done from primary database):
If your primary is using an spfile:
sqlplus “/ as sysdba”
SQL> create pfile=’$ORACLE_HOME/dbs/initPROD2.ora’from spfile;
Else, if your primary is using a pfile:
cp -p $ORACLE_HOME/dbs/initPROD.ora
$ORACLE_HOME/dbs/initPROD2.ora
Note: We will be modifying both the primary and standby parameter files to handle being in either the primary or the standby mode for quick switchovers.
Standby Database Parameters (changes in copy of primary’s values):Change pathnames, such as control_files, background_dump_dest,core_dump_dest, user_dump_dest, and audit_file_dest, and add:
# log_archive_dest = /orcl/oradata/PROD2/archivelogs
log_archive_dest_1 = ‘LOCATION=/orcl/oradata/PROD2/archivelogs MANDATORY’ # for switchover
log_archive_dest_state_1 = ENABLE # for switchover
log_archive_dest_2 = ‘SERVICE=myserver_prod LGWR SYNC’ # for switchover
log_archive_dest_state_2 = ENABLE # for switchover
standby_archive_dest = /orcl/oradata/PROD2/archivelogs
standby_file_management = AUTO # or MANUAL for raw devices
remote_archive_enable = TRUE # TRUE or RECEIVE, change RECEIVE to SEND on switchover
instance_name = PROD2
lock_name_space = PROD2 # use when primary and standby on same system; same as instance_name
fal_server = myserver_prod # “fal” is Fetch Archive Log, for log gap resolution
fal_client = myserver_prod2
db_file_name_convert = (‘/PROD/’,’/PROD2/’)
log_file_name_convert = (‘/PROD/’,’/PROD2/’)
Primary Database Parameters (changes in primary’s values):#log_archive_dest = /orcl/oradata/PROD/archivelogs
log_archive_dest_1 = ‘LOCATION=/orcl/oradata/PROD/archivelogs MANDATORY’
log_archive_dest_state_1 = ENABLE
log_archive_dest_2 = ‘SERVICE=myserver_prod2 LGWR SYNC’
log_archive_dest_state_2 = ENABLE
standby_archive_dest = /orcl/oradata/PROD/archivelogs # for switchover
standby_file_management = AUTO # for switchover; or MANUAL for raw devices
remote_archive_enable = TRUE # TRUE or SEND, change SEND to RECEIVE on switchover
instance_name = PROD
lock_name_space = PROD # use when primary and standby on same system; same as instance_name
fal_server = myserver_prod2 # for switchover
fal_client = myserver_prod # for switchover
db_file_name_convert = (‘/PROD2/’,’/PROD/’) # for switchover
log_file_name_convert = (‘/PROD2/’,’/PROD/’) # for switchover
(If primary uses spfile, wait until after the standby databasefiles are copied/created to make these parameter changes.)
Standby Database Datafiles, etc.Create the standby control file from the primary database:
SQL> alter database create standby controlfile as ‘/orcl/oradata/PROD2/ctrl_PROD_01.ctl';
Shut down the primary database and copy or FTP its datafiles, redo log files, and the just-created standby parameter file and standby control file, to the standby site.
SQL> select force_logging from v$database;
SQL> alter database force logging;
ARCHIVELOG mode and automatic archiving must be enabled:
SQL> archive log list
MAXLOGFILES >= (2 * Current Redo Log Groups) + 1:
SQL> select records_used “Current Groups”,records_total “Max Groups” from v$controlfile_record_section where type = ‘REDO LOG';
listener.ora Additions:Define the standby database SID on the standby site:
(SID_DESC=
(SID_NAME=PROD2)
(ORACLE_HOME=/pgms/oracle/product/v9204)
)
(in $ORACLE_HOME/network/admin/listener.ora)
tnsnames.ora Additions:Define the standby database connect string on the primary site:
myserver_prod2 =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS =(PROTOCOL = TCP) (Host = 123.45.67.89) — whatever host IP has PROD2(Port = 1521)
) )
(CONNECT_DATA = (SID = PROD2) ) )
(define myserver_prod and myserver_prod2 on both primary and standby sites for quick switchovers)
sqlnet.ora and /etc/oratab Additions:Enable dead connection detection on the primary and standby sites:
sqlnet.expire_time=2
(in $ORACLE_HOME/network/admin/sqlnet.ora)
Add the standby database’s entry to /etc/oratab on the standby site:
PROD2:/pgms/oracle/product/v9204:N
Standby Database Parameter File:Create the initPROD2.ora parameter file to be used for the standby database (done from primary database):
If your primary is using an spfile:
sqlplus “/ as sysdba”
SQL> create pfile=’$ORACLE_HOME/dbs/initPROD2.ora’from spfile;
Else, if your primary is using a pfile:
cp -p $ORACLE_HOME/dbs/initPROD.ora
$ORACLE_HOME/dbs/initPROD2.ora
Note: We will be modifying both the primary and standby parameter files to handle being in either the primary or the standby mode for quick switchovers.
Standby Database Parameters (changes in copy of primary’s values):Change pathnames, such as control_files, background_dump_dest,core_dump_dest, user_dump_dest, and audit_file_dest, and add:
# log_archive_dest = /orcl/oradata/PROD2/archivelogs
log_archive_dest_1 = ‘LOCATION=/orcl/oradata/PROD2/archivelogs MANDATORY’ # for switchover
log_archive_dest_state_1 = ENABLE # for switchover
log_archive_dest_2 = ‘SERVICE=myserver_prod LGWR SYNC’ # for switchover
log_archive_dest_state_2 = ENABLE # for switchover
standby_archive_dest = /orcl/oradata/PROD2/archivelogs
standby_file_management = AUTO # or MANUAL for raw devices
remote_archive_enable = TRUE # TRUE or RECEIVE, change RECEIVE to SEND on switchover
instance_name = PROD2
lock_name_space = PROD2 # use when primary and standby on same system; same as instance_name
fal_server = myserver_prod # “fal” is Fetch Archive Log, for log gap resolution
fal_client = myserver_prod2
db_file_name_convert = (‘/PROD/’,’/PROD2/’)
log_file_name_convert = (‘/PROD/’,’/PROD2/’)
Primary Database Parameters (changes in primary’s values):#log_archive_dest = /orcl/oradata/PROD/archivelogs
log_archive_dest_1 = ‘LOCATION=/orcl/oradata/PROD/archivelogs MANDATORY’
log_archive_dest_state_1 = ENABLE
log_archive_dest_2 = ‘SERVICE=myserver_prod2 LGWR SYNC’
log_archive_dest_state_2 = ENABLE
standby_archive_dest = /orcl/oradata/PROD/archivelogs # for switchover
standby_file_management = AUTO # for switchover; or MANUAL for raw devices
remote_archive_enable = TRUE # TRUE or SEND, change SEND to RECEIVE on switchover
instance_name = PROD
lock_name_space = PROD # use when primary and standby on same system; same as instance_name
fal_server = myserver_prod2 # for switchover
fal_client = myserver_prod # for switchover
db_file_name_convert = (‘/PROD2/’,’/PROD/’) # for switchover
log_file_name_convert = (‘/PROD2/’,’/PROD/’) # for switchover
(If primary uses spfile, wait until after the standby databasefiles are copied/created to make these parameter changes.)
Standby Database Datafiles, etc.Create the standby control file from the primary database:
SQL> alter database create standby controlfile as ‘/orcl/oradata/PROD2/ctrl_PROD_01.ctl';
Shut down the primary database and copy or FTP its datafiles, redo log files, and the just-created standby parameter file and standby control file, to the standby site.
Copy the standby control file on the standby site to the other file names listed in the control_files init.ora parameter.
Create the standby’s password file, if needed, on the standby site:
$ orapwd file=$ORACLE_HOME/dbs/orapwPROD2 password=<sys password> entries=5
$ orapwd file=$ORACLE_HOME/dbs/orapwPROD2 password=<sys password> entries=5
Reload the listener on the primary and standby sites:
$ lsnrctl reload
$ lsnrctl reload
Standby Database Startup:Start
the standby database in nomount mode, create the spfile if wanted,
mount the standby database, and change to managed recovery:
$ . oraenv PROD2
$ sqlplus “/ as sysdba”
SQL> create spfile from pfile;
SQL> startup nomount
SQL> alter database mount standby database;
SQL> alter database recover managed standby database disconnect from session;
SQL> exit
Primary Database Startup:If your primary is using an spfile, set the primary database parameters in the spfile as listed earlier. Sample “alter system” commands are shown below:
SQL> startup nomount
SQL> alter system reset log_archive_dest scope=spfile sid=’*';
SQL> alter system set log_archive_dest_1 = ‘LOCATION=/orcl/oradata/PROD/archivelogs MANDATORY’ scope=spfile;… etc
SQL> shutdown
Start up the primary database with the new parameters:
$ . oraenv PROD2
$ sqlplus “/ as sysdba”
SQL> create spfile from pfile;
SQL> startup nomount
SQL> alter database mount standby database;
SQL> alter database recover managed standby database disconnect from session;
SQL> exit
Primary Database Startup:If your primary is using an spfile, set the primary database parameters in the spfile as listed earlier. Sample “alter system” commands are shown below:
SQL> startup nomount
SQL> alter system reset log_archive_dest scope=spfile sid=’*';
SQL> alter system set log_archive_dest_1 = ‘LOCATION=/orcl/oradata/PROD/archivelogs MANDATORY’ scope=spfile;… etc
SQL> shutdown
Start up the primary database with the new parameters:
SQL> startup
Start archiving to the standby database by issuing a log switch:
SQL> alter system switch logfile;
Congratulations!!! You now have a working standby database for your primary database
Add Standby Redo Log Groups to Standby Database
Create standby redo log groups on standby database (start with next
group number; create one more group than current number of groups) after
switching out of managed recovery mode:
SQL> sqlplus “/ as sysdba”
SQL> alter database recover managed standby database cancel;
SQL> alter database open read only;
SQL> select max(group#) maxgroup from v$logfile;
SQL> select max(bytes) / 1024 “size (K)” from v$log;
SQL> alter database add standby logfile group 4
(‘/orcl/oradata/PROD2/stby_log_PROD_4A.rdo’,’/orcl/oradata/PROD2/stby_log_PROD_4B.rdo’)
size 4096K; … etc …
SQL> column member format a55
SQL> select vs.group#,vs.bytes,vl.member from v$standby_log vs,v$logfile vl where vs.group# = vl.group# order by vs.group#,vl.member;
Add Tempfile To Standby
Add a tempfile to the standby database for switchover or read-only access, then, switch back to managed recovery:
SQL> alter tablespace temp add tempfile ‘/data/oradata/PROD2/temp_PROD_01.dbf’ size 400064K reuse;
SQL> alter database recover managed standby database disconnect from session;
SQL> select * from v$tempfile;
SQL> exit
Add Standby Redo Log Groups to Primary Database
Create standby logfile groups on the primary database for switchovers
(start with next group number; create one more group than current number
of groups):
$ sqlplus “/ as sysdba”
SQL> select max(group#) maxgroup from v$logfile;
SQL> select max(bytes) / 1024 “size (K)” from v$log;
SQL> select max(bytes) / 1024 “size (K)” from v$log;
SQL> alter database add standby logfile group 4
(‘/orcl/oradata/PROD/stby_log_PROD_4A.rdo’,
‘/orcl/oradata/PROD/stby_log_PROD_4B.rdo’) size 4096K; … etc …
SQL> column member format a55
SQL> select vs.group#,vs.bytes,vl.member from v$standby_log vs, v$logfile vl where vs.group# = vl.group# order by vs.group#,vl.member;
SQL> select vs.group#,vs.bytes,vl.member from v$standby_log vs, v$logfile vl where vs.group# = vl.group# order by vs.group#,vl.member;
Switch To Maximum Availability Protection Mode
Switch to the desired “maximum availability” protection mode on the primary database (from the default “maximum performance”):
SQL> select value from v$parameter where name = ‘log_archive_dest_2′; — must show LGWR SYNC
SQL> shutdown normal
SQL> startup mount
SQL> alter database set standby database to maximize availability;
SQL> alter database open;
SQL> select protection_mode from v$database;
Test Updates Propagating to Standby
Try some edits on the primary and check to see that the changes made it to the standby:
On the primary:
SQL> update spriden set spriden_first_name = ‘James’ where spriden_pidm = 1234 and spriden_change_ind is null;
SQL> commit;
SQL> alter system switch logfile;
On the standby (wait a few seconds first):
SQL> alter database recover managed standby database cancel;
SQL> alter database open read only;
SQL> select * from spriden where spriden_pidm = 1234 and spriden_change_ind is null;
SQL> alter database recover managed standby database disconnect from session;
Running Reports with a Standby
Set standby to Read Only to run reports:
SQL> alter database recover managed standby database cancel;
SQL> alter database open read only;
SQL> @myreport.sql
SQL> alter database recover managed standby database disconnect from session;
Shutdown and Startup for Standby Database
To shut down a standby database:
If in read-only access, switch back to managed recovery (after terminating any other active sessions):
SQL> alter database recover managed standby database disconnect from session;
Cancel managed recovery and shutdown:
SQL> alter database recover managed standby database cancel;
SQL> shutdown immediate
To start up a standby database:
SQL> startup nomount
SQL> alter database mount standby database;
SQL> alter database recover managed standby database disconnect from session;
Switchover – Swapping Primary and Standby
End all activities on the primary and standby database.
On the primary (switchover status should show “TO STANDBY”):
SQL> select database_role,switchover_status from v$database;
SQL> alter database commit to switchover to physical standby;
SQL> shutdown immediate
SQL> startup nomount
SQL> alter database mount standby database;
On the standby (switchover status should show “SWITCHOVER PENDING”):
SQL> select database_role,switchover_status from v$database;
SQL> alter database commit to switchover to primary;
SQL> shutdown normal
SQL> startup
On the primary:SQL> alter database recover managed standby database disconnect from session;
On the standby:SQL> alter system archive log current;
Change tnsnames.ora entry on all servers to swap the connect strings (myserver_prod and myserver_prod2).
Failover – Standby Becomes Primary
End all activities on the standby database.
May need to resolve redo log gaps (not shown here).
On the standby: SQL> alter database recover managed standby database finish;
SQL> alter database commit to switchover to primary;
SQL> shutdown immediate
SQL> startup
Change tnsnames.ora entry on all servers to point the primary connect string to the standby database.
New standby needs to be created. Old primary is no longer functional.
Monitoring Standby Database
select count(*) from v$archive_gap;
This query detects gaps in the logs that have been received. If any rows are returned by
this query then there is a gap in the sequence numbers of the logs that have been received.
This gap must be resolved before logs can be applied.
SELECT decode(count(*),0,0,1) FROM v$managed_standby WHERE (PROCESS=’ARCH’ AND STATUS NOT
IN (‘CONNECTED’)) OR (PROCESS=’MRP0′ AND STATUS NOT IN (‘WAIT_FOR_LOG’,’APPLYING_LOG’))
OR (PROCESS=’RFS’ AND STATUS NOT IN (‘IDLE’,’RECEIVING’));
This query detects bad statuses. When a bad status is present this query will return a “1”.
The ‘ARCH’ process should always be ‘CONNECTED’. The ‘MRP0′ process
should always be waiting for a log or applying a log, and when this is
not true it will report the error in the status. The ‘RFS’ process
exists when the Primary is connected to the Standby and should always be
‘IDLE’ or ‘RECEIVING’.
SELECT DECODE(COUNT(DISTINCT PROCESS),3,0,1)
FROM v$managed_standby;
This query detects missing processes. If we do not have exactly 3
distinct processes then there is a problem, and this query will return a
“1”.
The most likely process to be missing is the ‘RFS’ which is the
connection to the Primary database. You must resolve the problem
preventing the Primary from connecting to the Standby before this
process will start running again.
Verify all STANDBY PROCESSES are running normally on the STANDBY database.
SELECT PROCESS,STATUS,RESETLOG_ID,SEQUENCE#,ACTIVE_AGENTS
FROM V$MANAGED_STANDBY ;
A query with good results follows proving all processes are connected
with normal statuses.
SELECT SEQUENCE#, FIRST_TIME, NEXT_TIME, APPLIED
FROM V$ARCHIVED_LOG
WHERE FIRST_TIME > TRUNC(SYSDATE)
ORDER BY SEQUENCE#;
Data guard Related View
V$DATABASE
PROTECTION_LEVEL: current protection mode setting.
FS_FAILOVER_STATUS: synchronization status
DBA_LOGSTDBY_UNSUPPORTED: unsupported tables.
DBA_LOGSTDBY_EVENTS: monitor transaction activity.
V$LOG: Redo log changed.
V$MANAGED_STANDBY : Recovery progress.
Oracle Data Guard Concept
Oracle Data Guard is one of the most effective and comprehensive
data availability, data protection and disaster recovery solutions
available today for enterprise data.
Oracle Data Guard is the management, monitoring, and automation software
infrastructure that creates, maintains, and monitors one or more
standby databases to protect enterprise data from failures, disasters,
errors, and corruptions.
Data Guard maintains these standby databases as transitional consistent
copies of the production database. These standby databases can be
located at remote disaster recovery sites thousands of miles away from
the production data center, or they may be located in the same city,
same campus, or even in the same building. If the production database
becomes unavailable because of a planned or an unplanned outage, Data
Guard can switch any standby database to the production role, thus
minimizing the downtime associated with the outage, and preventing any
data loss.
Available as a feature of the Enterprise Edition of the Oracle Database, Data Guard can be used in combination with other Oracle High Availability (HA) solutions such as Real Application Clusters (RAC), Oracle Flashback and Oracle Recovery Manager (RMAN), to provide a very high level of data protection and data availability that is unprecedented in the industry.
The following diagram presents a hi-level overview of Oracle Data Guard.
Overview of Oracle Data Guard Functional Components
Data Guard Configuration:
A Data Guard configuration consists of one production (or primary)
database and up to nine standby databases. The databases in a Data Guard
configuration are connected by Oracle Net and may be dispersed
geographically. There are no restrictions on where the databases are
located, provided that they can communicate with each other. However,
for disaster recovery, it is recommended that the standby databases are
hosted at sites that are geographically separated from the primary site.
Redo Apply and SQL Apply:
A standby database is initially created from a backup copy of the
primary database. Once created, Data Guard automatically maintains the
standby database as a transactional consistent copy of the primary
database by transmitting primary database redo data to the standby
system and then applying the redo logs to the standby database.
Data Guard provides two methods to apply this redo data to the standby
database and keep it transactional consistent with the primary, and
these methods correspond to the two types of standby databases supported
by Data Guard.
- Redo Apply, used for physical standby databases
- SQL Apply, used for logical standby databases
A physical standby database provides a physically identical copy of the
primary database, with on-disk database structures that are identical to
the primary database on a block-for-block basis. The database schemas,
including indexes are the same. The Redo Apply technology applies redoes
data on the physical standby database using standard Oracle media
recovery techniques.
A logical standby database contains the same logical information as the
production database, although the physical organization and structure of
the data can be different. The SQL apply technology keeps the logical
standby database synchronized with the primary database by transforming
the data in the redo logs received from the primary database into SQL
statements and then executing the SQL statements on the standby
database. This makes it possible for the logical standby database to be
accessed for queries and reporting purposes at the same time the SQL is
being applied to it. Thus, a logical standby database can be used
concurrently for data protection and reporting.
Role Management:
Using Data Guard, the role of a database can be switched from a primary
role to a standby role and vice versa, ensuring no data loss in the
process, and minimizing downtime. There are two kinds of role
transitions – a switchover and a failover. A switchover is a role
reversal between the primary database and one of its standby databases.
This is typically done for planned maintenance of the primary system.
During a switchover, the primary database transitions to a standby role
and the standby database transitions to the primary role. The transition
occurs without having to re-create either database. A failover is an
irreversible transition of a standby database to the primary role. This
is only done in the event of a catastrophic failure of the primary
database, which is assumed to be lost and to be used again in the Data
Guard configuration, it must be re-instantiated as a standby from the
new primary.
Data Guard Protection Modes:
In some situations, a business cannot afford to lose data at any cost.
In other situations, some applications require maximum database
performance and can tolerate a potential loss of data. Data Guard
provides three distinct modes of data protection to satisfy these varied
requirements:
- Maximum Protection— This mode offers the highest level of data protection. Data is synchronously transmitted to the standby database from the primary database and transactions are not committed on the primary database unless the redo data is available on at least one standby database configured in this mode. If the last standby database configured in this mode becomes unavailable, processing stops on the primary database. This mode ensures no-data-loss.
- Maximum Availability— This mode is similar to the maximum protection mode, including zero data loss. However, if a standby database becomes unavailable (for example, because of network connectivity problems), processing continues on the primary database. When the fault is corrected, the standby database is automatically resynchronized with the primary database.
- Maximum Performance— This mode offers slightly less data protection on the primary database, but higher performance than maximum availability mode. In this mode, as the primary database processes transactions, redo data is asynchronously shipped to the standby database. The commit operation of the primary database does not wait for the standby database to acknowledge receipt of redo data before completing write operations on the primary database. If any standby destination becomes unavailable, processing continues on the primary database and there is little effect on primary database performance.
Data Guard Broker:
The Oracle Data Guard Broker is a distributed management framework that
automates and centralizes the creation, maintenance, and monitoring of
Data Guard configurations. All management operations can be performed
either through Oracle Enterprise Manager, which uses the Broker, or
through the Broker’s specialized command-line interface (DGMGRL).
Data Guard Architecture Diagram
The following diagram shows an overview of the Oracle Data Guard architecture.
What’s New in Oracle Data Guard 10g Release 2?
This section will highlight some of the key new features of Oracle Data Guard 10g Release 2. For details into these features, please refer to the following:
Fast-Start Failover
This capability allows Data Guard to automatically, and quickly fail
over to a previously chosen, synchronized standby database in the event
of loss of the primary database, without requiring any manual steps to
invoke the failover, and without incurring any data loss. Following a
fast-start failover, once the old primary database is repaired, Data
Guard automatically reinstates it to be a standby database. This act
restores high availability to the Data Guard configuration.
Improved Redo Transmission
Several enhancements have been made in the redo transmission
architecture to make sure redo data generated on the primary database
can be transmitted as quickly and efficiently as possible to the standby
database(s).
Easy conversion of a physical standby database to a reporting database
A physical standby database can be activated as a primary database,
opened read/write for reporting purposes, and then flashed back to a
point in the past to be easily converted back to a physical standby
database. At this point, Data Guard automatically synchronizes the
standby database with the primary database. This allows the physical
standby database to be utilized for read/write reporting and cloning
activities.
Automatic deletion of applied archived redo log files in logical standby databases
Archived logs, once they are applied on the logical standby database,
are automatically deleted, reducing storage consumption on the logical
standby and improving Data Guard manageability. Physical standby
databases have already had this functionality since Oracle Database 10g Release 1, with Flash Recovery Area.
Fine-grained monitoring of Data Guard configurations
Oracle Enterprise Manager has been enhanced to provide granular,
up-to-date monitoring of Data Guard configurations, so that
administrators may make an informed and expedient decision regarding
managing this configuration.
What’s New in Oracle Data Guard 10g Release 1?
This section will highlight some of the key new features of Oracle Data Guard 10g Release 1. For details into these features, please refer to the following:
General New Features:
Real Time Apply:
With this feature, redo data can be applied on the standby database
(whether Redo Apply or SQL Apply) as soon as they have written to a
Standby Redo Log (SRL). Prior releases of Data Guard require this redo
data to be archived at the standby database in the form of archivelogs
before they can be applied.
The Real Time Apply feature allows standby databases to be closely
synchronized with the primary database, enabling up-to-date and
real-time reporting (especially for Data Guard SQL Apply). This also
enables faster switchover and failover times, which in turn reduces
planned and unplanned downtime for the business.
The impact of a disaster is often measured in terms of Recovery Point
Objective (RPO – i.e. how much data can a business afford to lose in the
event of a disaster) and Recovery Time Objective (RTO – i.e. how much
time a business can afford to be down in the event of a disaster). With
Oracle Data Guard, when Maximum Protection is used in combination with
Real Time Apply, businesses get the benefits of both zero data loss as
well as minimal downtime in the event of a disaster and this makes
Oracle Data Guard the only solution available today with the best RPO
and RTO benefits for a business.
Integration with Flashback Database:
Data Guard in 10g has been integrated with the Flashback family
of features to bring the Flashback feature benefits to a Data Guard
configuration.
One such benefit is human error protection. In Oracle9i, administrators may configure Data Guard with an apply delay to
protect standby databases from possible logical data corruptions that
occurred on the primary database. The side-effects of such delays are
that any reporting that gets done on the standby database is done on old
data, and switchover/failover gets delayed because the accumulated logs
have to be applied first. In Data Guard 10g, with the Real
Time Apply feature, such delayed-reporting or
delayed-switchover/failover issues do not exist, and – if logical
corruptions do land up affecting both the primary and standby database,
the administrator may decide to use Flashback Database on both the
primary and standby databases to quickly revert the databases to an
earlier point-in-time to back out such user errors.
Another benefit that such integration provides is during failovers. In releases prior to 10g,
following any failover operation, the old primary database must be
recreated (as a new standby database) from a backup of the new primary
database, if the administrator intends to bring it back in the Data
Guard configuration. This may be an issue when the database sizes are
fairly large, and the primary/standby databases are hundreds/thousands
of miles away. However, in Data Guard 10g, after the primary
server fault is repaired, the primary database may simply be brought up
in mounted mode, “flashed back” (using flashback database) to
the SCN at which the failover occurred, and then brought back as a
standby database in the Data Guard configuration. No re-instantiation is
required.
SQL Apply New Features:
Zero Downtime Instantiation:
Logical standby database can now be created from an online backup of the
primary database, without shutting down or quiescing the primary
database, as was the case in prior releases. No shutdown of the primary
system implies production downtime is eliminated, and no quiesce implies
no waiting for quiescing to take effect and no dependence on Resource
Manager.
Rolling Upgrades:
Oracle Database 10g supports database software upgrades (from Oracle Database 10g Patchset
1 onwards) in a rolling fashion, with near zero database downtime, by
using Data Guard SQL Apply. The steps involve upgrading the logical
standby database to the next release, running in a mixed mode to test
and validate the upgrade, doing a role reversal by switching over to the
upgraded database, and then finally upgrading the old primary database.
While running in a mixed mode for testing purpose, the upgrade can be
aborted and the software downgraded, without data loss. For additional
data protection during these steps, a second standby database may be
used.
By supporting rolling upgrades with minimal downtimes, Data Guard
reduces the large maintenance windows typical of many administrative
tasks, and enables the 24×7 operation of the business.
Additional Datatypes:
SQL Apply now supports the following additional data types.
- NCLOB
- LONG
- LONG RAW
- BINARY_FLOAT
- BINARY_DOUBLE
- IOT-s (without overflows and without LOB columns)
This support for additional datatypes allows logical standby databases
to recover and protect a wider variety of data, thus increasing the
overall database protection and recovery options for Data Guard.
Enterprise Manager / Data Guard Broker New Features:
RAC Support:
It is now possible to use the Data Guard Broker, and the Broker’s
Command Line Interface (DGMGRL), as well as Enterprise Manager, to
create and manage Data Guard configurations that contain RAC primary and
RAC standby databases. In Oracle9i, such administration is possible only through SQL*Plus. In Data Guard 10g,
Data Guard Broker interfaces with Oracle Clusterware such that it has
control over critical operations during specific Data Guard state
transitions, such as switchovers, failovers, protection mode changes and
state changes.
Simplified Browser-based Interface
Administration of a Data Guard configuration can be done through the new
streamlined browser-based HTML interface of Enterprise Manager that
enables complete standby database lifecycle management. The focus of
such streamlined administration is on:
- Ease of use.
- Management based on best practices.
- Pre-built integration with other HA features.
Data Guard Benefits
- Disaster recovery and high availabilityData Guard provides an efficient and comprehensive disaster recovery and high availability solution. Automatic failover and easy-to-manage switchover capabilities allow quick role reversals between primary and standby databases, minimizing the downtime of the primary database for planned and unplanned outages.
- Complete data protectionA standby database also provides an effective safeguard against data corruptions and user errors. Storage level physical corruptions on the primary database do not propagate to the standby database. Similarly, logical corruptions or user errors that cause the primary database to be permanently damaged can be resolved. Finally, the redo data is validated at the time it is received at the standby database and further when applied to the standby database.
- Efficient utilization of system resourcesA physical standby database can be used for backups and read-only reporting, thereby reducing the primary database workload and saving valuable CPU and I/O cycles. In Oracle Database 10g Release 2, a physical standby database can also be easily converted back and forth between being a physical standby database and an open read/write database. A logical standby database allows its tables to be simultaneously available for read-only access while they are updated from the primary database. A logical standby database also allows users to perform data manipulation operations on tables that are not updated from the primary database. Finally, additional indexes and materialized views can be created in the logical standby database for better reporting performance.
- Flexibility in data protection to balance availability against performance requirementsOracle Data Guard offers the maximum protection, maximum availability, and maximum performance modes to help enterprises balance data availability against system performance requirements.
- Protection from communication failuresIf network connectivity is lost between the primary and one or more standby databases, redo data cannot be sent from the primary to those standby databases. Once connectivity is re-established, the missing redo data is automatically detected by Data Guard and the necessary archive logs are automatically transmitted to the standby databases. The standby databases are resynchronized with the primary database, with no manual intervention by the administrator.
- Centralized and simple managementData Guard Broker automates the management and monitoring tasks across the multiple databases in a Data Guard configuration. Administrators may use either Oracle Enterprise Manager or the Broker’s own specialized command-line interface (DGMGRL) to take advantage of this integrated management framework.
Integrated with Oracle databaseData Guard is available as an integrated feature of the Oracle Database (Enterprise Edition) at no extra cost.
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