很多朋友一直对DataGuard的fast-start failover持怀疑的态度;通过observer的观察，(Fast-Start Failover)FSFO提供了一种在primary数据库不可用情况下自动故障切换到standby数据库的能力。造成很多朋友不愿意使用FSFO的原因之一是故障切换后不得不重建原primary数据库，不过如果我们能配合使用10g中的闪回数据库特性的话，这一重建数据库的工作便也可以一劳永逸了。
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/* 启用fast_start failover的前提之一是在
primary
和standby库上都启用flashback
database
*/
SQL>
select
*
from
v$version;
BANNER
--------------------------------------------------------------------------------
Oracle
Database
11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production
PL/SQL Release 11.2.0.2.0 - Production
CORE 11.2.0.2.0 Production
TNS
for
Linux: Version 11.2.0.2.0 - Production
NLSRTL Version 11.2.0.2.0 - Production
/* 当前的
primary
库情况 */
SQL>
select
open_mode ,database_role,flashback_on
from
v$
database
;
OPEN_MODE DATABASE_ROLE FLASHBACK_ON
-------------------- ---------------- ------------------
READ
WRITE
PRIMARY
YES
SQL>
alter
session
set
nls_date_format=
'YYYY-MM-DD hh24:mi:ss'
;
Session altered.
SQL>
select
OLDEST_FLASHBACK_TIME
from
v$flashback_database_log;
OLDEST_FLASHBACK_TI
-------------------
2011-02-19 22:40:39
/* 当前的standby库情况 */
SQL>
select
open_mode ,database_role,flashback_on
from
v$
database
;
OPEN_MODE DATABASE_ROLE FLASHBACK_ON
-------------------- ---------------- ------------------
READ
ONLY
WITH
APPLY PHYSICAL STANDBY YES
SQL>
alter
session
set
nls_date_format=
'YYYY-MM-DD hh24:mi:ss'
;
Session altered.
SQL>
select
OLDEST_FLASHBACK_TIME
from
v$flashback_database_log;
OLDEST_FLASHBACK_TI
-------------------
2011-02-19 22:34:56
DGMGRL> edit configuration
set
property faststartfailoverthreshold=10;
Property
"faststartfailoverthreshold"
updated
DGMGRL> show configuration verbose;
Configuration - pro
Protection Mode: MaxAvailability
Databases:
sbdb -
Primary
database
prod - Physical standby
database
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS
/* 另开一个终端启动observer */
DGMGRL> start observer
Observer started
DGMGRL> show fast_start failover
Fast-Start Failover: DISABLED
Threshold: 10 seconds
Target: (none)
Observer: rh3.oracle.com
Lag Limit: 30 seconds
Shutdown
Primary
:
TRUE
Auto-reinstate:
TRUE
Configurable Failover Conditions
Health Conditions:
Corrupted Controlfile YES
Corrupted Dictionary YES
Inaccessible Logfile
NO
Stuck Archiver
NO
Datafile Offline YES
Oracle Error Conditions:
(none)
/* 启动快速故障切换 */
DGMGRL> enable fast_start failover
Enabled.
/* 记录实际切换前的时间 */
[maclean@rh3 ~]$
date
Sat Feb 19 23:35:44 CST 2011
[maclean@rh2 ~]$ ps -ef|grep pmon|grep -v grep
maclean 25165 1 0 22:58 ? 00:00:00 ora_pmon_SBDB
maclean 26080 1 0 23:04 ? 00:00:00 ora_pmon_PROD
[maclean@rh2 ~]$ kill -9 25165
/* 通过kill pmon进程造成主库crash，引发fast-start failover */
/* observer观察到
primary
库意外终止后，实施了快速故障切换 */
23:37:27.92 Saturday, February 19, 2011
Initiating Fast-Start Failover
to
database
"prod"
...
Performing failover NOW, please wait...
Failover succeeded, new
primary
is
"prod"
23:37:33.69 Saturday, February 19, 2011
23:39:17.98 Saturday, February 19, 2011
Initiating reinstatement
for
database
"sbdb"
...
Reinstating
database
"sbdb"
, please wait...
Error: ORA-16653: failed
to
reinstate
database
Failed.
Reinstatement
of
database
"sbdb"
failed
23:39:26.30 Saturday, February 19, 2011
23:40:05.00 Saturday, February 19, 2011
Initiating reinstatement
for
database
"sbdb"
...
Reinstating
database
"sbdb"
, please wait...
Error: ORA-16653: failed
to
reinstate
database
Failed.
Reinstatement
of
database
"sbdb"
failed
23:40:09.24 Saturday, February 19, 2011
/* 接下来我们通过闪回数据库来将失败切换后的
primary
库flashback到faliover之前以便重用*/
SQL> startup mount;
SQL> flashback
database
to
timestamp
to_timestamp(
'2011-02-19 23:30:44'
,
'YYYY-MM-DD hh24:mi:ss'
);
flashback
database
to
timestamp
to_timestamp(
'2011-02-19 23:35:44'
,
'YYYY-MM-DD hh24:mi:ss'
)
*
ERROR
at
line 1:
ORA-38754: FLASHBACK
DATABASE
not
started; required redo log
is
not
available
ORA-38762: redo logs needed
for
SCN 1143987
to
SCN
End
-
of
-Redo
ORA-38761: redo log
sequence
10
in
thread 1, incarnation 3 could
not
be
accessed
/* 缺少最近的归档日志而无法完成闪回，需要到目前的
primary
库中查找 */
SQL>
select
name
from
v$archived_log
where
FIRST_CHANGE#<1143987
and
NEXT_CHANGE#>1143987;
NAME
--------------------------------------------------------------------------------
/s01/fast_recovery_area/PROD/archivelog/2011_02_19/o1_mf_1_10_6ozpzh9c_.arc
SQL>
alter
database
register physical logfile
'/s01/fast_recovery_area/PROD/archivelog/2011_02_19/o1_mf_1_10_6ozpzh9c_.arc'
;
Database
altered.
SQL> flashback
database
to
timestamp
to_timestamp(
'2011-02-19 23:30:44'
,
'YYYY-MM-DD hh24:mi:ss'
);
Flashback complete.
/* 成功闪回后，observer将主动去尝试reinstate这个目前可用的standby库,如以下日志*/
23:46:20.16 Saturday, February 19, 2011
Initiating reinstatement
for
database
"sbdb"
...
Reinstating
database
"sbdb"
, please wait...
Operation requires shutdown
of
instance
"SBDB"
on
database
"sbdb"
Shutting down instance
"SBDB"
...
ORA-01109:
database
not
open
Database
dismounted.
ORACLE instance shut down.
Operation requires startup
of
instance
"SBDB"
on
database
"sbdb"
Starting instance
"SBDB"
...
ORACLE instance started.
Database
mounted.
Continuing
to
reinstate
database
"sbdb"
...
Reinstatement
of
database
"sbdb"
succeeded
23:47:13.49 Saturday, February 19, 2011
DGMGRL> show configuration verbose
Configuration - pro
Protection Mode: MaxAvailability
Databases:
prod -
Primary
database
sbdb - (*) Physical standby
database
(*) Fast-Start Failover target
Fast-Start Failover: ENABLED
Threshold: 10 seconds
Target: sbdb
Observer: rh3.oracle.com
Lag Limit: 30 seconds (
not
in
use)
Shutdown
Primary
:
TRUE
Auto-reinstate:
TRUE
Configuration Status:
SUCCESS
/*可以通过show configuration命令监控到当前
primary
与standby库都处于可用状态，
且fast_start failover也为启用状态 */
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本文转自maclean_007 51CTO博客，原文链接:http://blog.51cto.com/maclean/1277710
