有关Oracle Data Guard Failover 的说明

在之前的两篇文章里都对oracle Data Guard的Failover 进行了说明，但是没有个系统的说明，所以在这篇把DG的Failover 做个系统的说明。

物理Data Guard 下Failover 时Redo 的处理问题

http://blog.csdn.net/tianlesoftware/archive/2010/11/05/5989638.aspx

Oracle Data Guard Linux 平台 Physical Standby 搭建实例

http://blog.csdn.net/tianlesoftware/archive/2010/04/30/5547565.aspx

Failover 是失败切换。 这种情况下切换对redo 的处理，就显的很重要。如果处理好，就不会有数据丢失。 否则就会有数据丢失。

在Oracle 11g里，Data Guard 切换多了一个新的功能：flush redo。

Flush 能把没有发送的redo 从主库传送到standby库。 只要主库能启动到mount 状态，那么Flush 就可以把没有发送的归档和current online redo 发送到备库。

Flush语法：

SQL> ALTER SYSTEM FLUSH REDO TO target_db_name;

这里的target_db_name 是我们在主库的db_unique_name 名称。 也就是在tnsnames.ora 文件配置的。 Flush 会将未发送的redo 从主库传到备库，并且等待redo 在standby 库上apply 之后返回成功。 所以只要Flush成功，那么Failover 就没有主句丢失。

如果说我们的Primary 已经不能启动到mount 状态，那么就只能按照之前的方法来。 Oracle 10g 下就是这么操作的。

一. 正常的Failover

1.1 检查Gap

sql> select thread#, low_sequence#, high_sequence# from v$archive_gap;

如果有，将对应的归档文件copy到备库，在注册它

sql>alter database register physical logfile 'filespec1';

注意： 如果有Gap存在，并且没有解决。 那么是不能正常的进行一个Failover。 只能进行一个强制的Failover。 这种情况下会有数据丢失。

sql> alter database activate physical standby database;

1.2 解决gap问题后，进行切换

1.2.1 取消Apply

SQL> recover managed standby database cancel;

1.2.2 结束Apply

（1）在oracle 10gR2 或之后的版本：如果在备用库上有备用库日志文件

SQL> alter database recover managed standby database finish; -- [force|wait|nowait]

在执行这个命令的时候，如果主库和备库之间的网络中断了。 那么备库的RFS进程就会等待网络的连接，直到TCP超时。 因此在这种情况下，我们就需要加上Foce 关键字。

（2）在oracle 10gR2之前的版本：没有备库日志文件

SQL> alter database recover managed standby database finish skip standby logfile;

注意：如果执行了这条命令，就不能在进行recover standby database;

1.2.3 将备库切换成主库

SQL> alter database commit to switchover to primary;

SQL> shutdown immediate;

SQL> startup

二. 强行切换（激活）

2.1 使用条件

当我们正常切换的时候，提示我们需要介质恢复的时候，就需要使用强行激活standby 库。 如：

SQL> ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY;

ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY

*

ERROR at line 1:

ORA-16139: media recovery required

2.2 强行激活下的 redo 问题

在这里需要说明一点，就是我们在主库commit 之后，然后shutdown abort， 这时候，主库的online redo 会自动的写入备库的最后一个归档文件里（大小会发生变化）。 我们在恢复的时候需要对备库的最后一个归档文件进行重新的注册。

sql>alter database register physical logfile 'filespec1';

如果说，主库OS是整个宕机了。 这个时候，online redo 是不会发送到备库。所以我们需要手工的将主库的所有online redo copy到备库。 然后进行recover。

步骤如下：

SQL> alter database recover managed standby database cancel;

Database altered.

SQL> recover standby database until cancel;

ORA-00279: change 509016 generated at 11/05/2010 11:40:27 needed for thread 1

ORA-00289: suggestion : /u01/archive/1_17_734225750.dbf

ORA-00280: change 509016 for thread 1 is in sequence #17

-- 默认情况下会提示需要归档17， 实际上这个序列为17的归档还没有生成，我们忽略它，使用我们刚才copy过来的redo 日志来恢复。

Specify log: {<RET>=suggested | filename | AUTO | CANCEL}

/u01/app/oracle/oradata/orcl/redo01.log -- 注意， 这个位置是我手动写的

Log applied.

Media recovery complete.

这里一次就搞定了。 实际上有三个redo，如果不确定使用哪个redo的，只能一个一个试。

当我们使用了recover standby database until cancel之后，只能使用强制激活备库，如果使用正常模式，会提示我们需要：

ORA-16139: media recovery required

2.3 强制激活备库：

sql> alter database recover managed standby database cancel;
sql> recover standby database until cancel;

sql>alter database activate standby database;
sql>shutdown immediate;

sql>startup

三. Switchover

3.1 主库操作：

（1）查看状态：

sql>select switchover_status from v$database;

（2）切换

sql> alter database commit to switchover to physical standby with session shutdown;

SQL> shutdown immediate;

SQL> startup;

SQL> alter database mount standby database;

SQL> recover managed standby database disconnect;

3.2 备库操作：

SQL> alter database commit to switchover to primary with session shutdown;

SQL> shutdown immediate

SQL> startup

四. 对Failover 过程的研究

4.1 Failover 日志

Thu Mar 17 15:01:47 2011

alter database activate standby database

Thu Mar 17 15:01:47 2011

ALTER DATABASE ACTIVATE [PHYSICAL] STANDBY DATABASE (dave)

--我们切换的时候，命令写全命令，db 自动补全了

RESETLOGS after complete recovery through change 1255060

Resetting resetlogs activation ID 808909668 (0x3036fb64)

-- resetlogs了. 这就以为着产生一个新的incarnation。 online redo 会被清空

Online log /u01/app/oracle/oradata/dave/redo01.log: Thread 1 Group 1 was previously cleared

Online log /u01/app/oracle/oradata/dave/redo02.log: Thread 1 Group 2 was previously cleared

Online log /u01/app/oracle/oradata/dave/redo03.log: Thread 1 Group 3 was previously cleared

Standby became primary SCN: 1255058

Thu Mar 17 15:01:48 2011

Setting recovery target incarnation to 3

--修改incarnation版本

Thu Mar 17 15:01:48 2011

Converting standby mount to primary mount.

--将standby 转成 primary

Thu Mar 17 15:01:48 2011

ACTIVATE STANDBY: Complete - Database mounted as primary (dave)

Completed: alter database activate standby database

--完成active

Thu Mar 17 15:01:59 2011

Shutting down instance: further logons disabled

--关闭实例

Thu Mar 17 15:01:59 2011

Stopping background process CJQ0

Thu Mar 17 15:01:59 2011

Stopping background process MMNL

Thu Mar 17 15:01:59 2011

Stopping background process MMON

Thu Mar 17 15:01:59 2011

Shutting down instance (immediate)

License high water mark = 7

Thu Mar 17 15:01:59 2011

Stopping Job queue slave processes, flags = 7

Thu Mar 17 15:01:59 2011

Job queue slave processes stopped

All dispatchers and shared servers shutdown

Thu Mar 17 15:02:35 2011

ARC1: Archival disabled due to shutdown: 1089

Shutting down archive processes

Archiving is disabled

Thu Mar 17 15:02:45 2011

ARCH shutting down

ARC0: Archival stopped

Thu Mar 17 15:02:50 2011

ARCH shutting down

ARC1: Archival stopped

Thu Mar 17 15:07:04 2011

SHUTDOWN: Active processes prevent shutdown operation

Thu Mar 17 15:07:50 2011

ALTER DATABASE CLOSE NORMAL

Thu Mar 17 15:07:50 2011

ORA-1109 signalled during: ALTER DATABASE CLOSE NORMAL...

Thu Mar 17 15:07:50 2011

ALTER DATABASE DISMOUNT

Completed: ALTER DATABASE DISMOUNT

ARCH: Archival disabled due to shutdown: 1089

Shutting down archive processes

Archiving is disabled

Archive process shutdown avoided: 0 active

ARCH: Archival disabled due to shutdown: 1089

Shutting down archive processes

Archiving is disabled

Archive process shutdown avoided: 0 active

Thu Mar 17 15:08:13 2011

Starting ORACLE instance (normal)

--开始重新启动实例

LICENSE_MAX_SESSION = 0

LICENSE_SESSIONS_WARNING = 0

Picked latch-free SCN scheme 2

Autotune of undo retention is turned on.

IMODE=BR

ILAT =18

LICENSE_MAX_USERS = 0

SYS auditing is disabled

ksdpec: called for event 13740 prior to event group initialization

Starting up ORACLE RDBMS Version: 10.2.0.4.0.

System parameters with non-default values:

processes = 150

__shared_pool_size = 113246208

__large_pool_size = 4194304

__java_pool_size = 25165824

__streams_pool_size = 0

nls_territory = AMERICA

sga_target = 247463936

control_files = /u01/app/oracle/oradata/dave/control01.ctl, /u01/app/oracle/oradata/dave/control02.ctl, /u01/app/oracle/oradata/dave/control03.ctl

db_block_size = 8192

__db_cache_size = 100663296

compatible = 10.2.0.1.0

log_archive_config = dg_config=(dave_pd,dave_st)

log_archive_dest_1 = location=/u01/archivelog valid_for=(all_logfiles,all_roles) db_unique_name=dave_st

log_archive_dest_2 = service=dave_pd reopen=120 lgwr async valid_for=(online_logfiles,primary_role) db_unique_name=dave_pd

log_archive_dest_state_1 = ENABLE

log_archive_dest_state_2 = ENABLE

standby_archive_dest = /u01/archivelog

fal_client = dave_st

fal_server = dave_pd

db_file_multiblock_read_count= 16

standby_file_management = AUTO

undo_management = AUTO

undo_tablespace = UNDOTBS1

remote_login_passwordfile= EXCLUSIVE

db_domain =

dispatchers = (PROTOCOL=TCP) (SERVICE=daveXDB)

job_queue_processes = 10

background_dump_dest = /u01/app/oracle/admin/dave/bdump

user_dump_dest = /u01/app/oracle/admin/dave/udump

core_dump_dest = /u01/app/oracle/admin/dave/cdump

audit_file_dest = /u01/app/oracle/admin/dave/adump

db_name = dave

db_unique_name = dave_st

open_cursors = 300

pga_aggregate_target = 81788928

PMON started with pid=2, OS id=5909

PSP0 started with pid=3, OS id=5911

MMAN started with pid=4, OS id=5913

DBW0 started with pid=5, OS id=5915

LGWR started with pid=6, OS id=5917

CKPT started with pid=7, OS id=5919

SMON started with pid=8, OS id=5921

RECO started with pid=9, OS id=5923

CJQ0 started with pid=10, OS id=5925

MMON started with pid=11, OS id=5927

Thu Mar 17 15:08:14 2011

starting up 1 dispatcher(s) for network address '(ADDRESS=(PARTIAL=YES)(PROTOCOL=TCP))'...

MMNL started with pid=12, OS id=5929

Thu Mar 17 15:08:14 2011

starting up 1 shared server(s) ...

Thu Mar 17 15:08:15 2011

ALTER DATABASE MOUNT

Thu Mar 17 15:08:19 2011

Setting recovery target incarnation to 3

Thu Mar 17 15:08:19 2011

Successful mount of redo thread 1, with mount id 808884895

Thu Mar 17 15:08:19 2011

Database mounted in Exclusive Mode

Completed: ALTER DATABASE MOUNT

Thu Mar 17 15:08:19 2011

ALTER DATABASE OPEN

Thu Mar 17 15:08:19 2011

Assigning activation ID 808884895 (0x30369a9f)

LGWR: STARTING ARCH PROCESSES

ARC0 started with pid=16, OS id=5937

Thu Mar 17 15:08:19 2011

ARC0: Archival started

ARC1: Archival started

LGWR: STARTING ARCH PROCESSES COMPLETE

ARC1 started with pid=17, OS id=5939

LNS1 started with pid=18, OS id=5941

Thu Mar 17 15:08:22 2011

Thread 1 advanced to log sequence 2 (thread open)

Thu Mar 17 15:08:23 2011

ARC0: STARTING ARCH PROCESSES

Thu Mar 17 15:08:23 2011

ARC1: Becoming the 'no FAL' ARCH

ARC1: Becoming the 'no SRL' ARCH

Thu Mar 17 15:08:23 2011

Thread 1 opened at log sequence 2

Current log# 2 seq# 2 mem# 0: /u01/app/oracle/oradata/dave/redo02.log

Successful open of redo thread 1

Thu Mar 17 15:08:23 2011

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

LGWR: Setting 'active' archival for destination LOG_ARCHIVE_DEST_2

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

Thu Mar 17 15:08:23 2011

ARC1: LGWR is actively archiving destination LOG_ARCHIVE_DEST_2

Thu Mar 17 15:08:23 2011

ARC2: Archival started

ARC0: STARTING ARCH PROCESSES COMPLETE

ARC0: Becoming the heartbeat ARCH

ARC2 started with pid=19, OS id=5943

Thu Mar 17 15:08:23 2011

MTTR advisory is disabled because FAST_START_MTTR_TARGET is not set

Thu Mar 17 15:08:23 2011

SMON: enabling cache recovery

Thu Mar 17 15:08:24 2011

Successfully onlined Undo Tablespace 1.

Dictionary check beginning

Dictionary check complete

Thu Mar 17 15:08:24 2011

SMON: enabling tx recovery

Thu Mar 17 15:08:24 2011

Database Characterset is ZHS16GBK

Opening with internal Resource Manager plan

where NUMA PG = 1, CPUs = 1

replication_dependency_tracking turned off (no async multimaster replication found)

Starting background process QMNC

QMNC started with pid=20, OS id=5945

Thu Mar 17 15:08:26 2011

LOGSTDBY: Validating controlfile with logical metadata

Thu Mar 17 15:08:26 2011

LOGSTDBY: Validation complete

Completed: ALTER DATABASE OPEN

4.2 对Failover 的补充说明

在4.1 中看了Failover 的整个过程，DB 会进行一次resetlogs。 这个是个很有意思的过程。

（1） resetlogs 会产生一个新的incarnation。 这个会影响我们的RMAN 恢复。 我们查看一下：

RMAN> list incarnation;

List of Database Incarnations

DB Key Inc Key DB Name DB ID STATUS Reset SCN Reset Time

------- ------- -------- ---------------- --- ---------- ----------

1 1 DAVE 808637274 PARENT 1 30-JUN-05

2 2 DAVE 808637274 PARENT 446075 14-MAR-11

3 3 DAVE 808637274 CURRENT 1255061 17-MAR-11

这个时候，我们只能恢复incarnation 为3之内的信息，如果要恢复到其他版本的信息，要保证对应备份集存在的同时，在使用reset database incarnation to 3或者其他的版本。 之后在恢复。

（2）看下归档日志

先看备库：

SQL> select max(sequence#) from v$archived_log;

MAX(SEQUENCE#)

--------------

6

SQL> select sequence#,applied from v$archived_log;

SEQUENCE# APP

---------- ---

3 YES

2 YES

5 YES

4 YES

6 YES

这个是重新开始的，没有什么问题。

我们看下主库：

SQL> select max(sequence#) from v$archived_log;

MAX(SEQUENCE#)

--------------

88

SQL> select sequence#,applied from v$archived_log;

SEQUENCE# APP

---------- ---

4 YES

3 YES

5 YES

6 YES

7 YES

8 YES

......

82 YES

83 YES

84 YES

85 YES

86 YES

87 YES

88 YES

2 NO

2 YES --注意这部分，有重新开始了。

3 NO

3 YES

4 NO

5 NO

5 YES

4 YES

6 NO

6 YES

因为resetlogs 会重置sequence#。 将其设置为1. 所以这里又重新开始了。 但是SCN 不会重置。 我们查看一下：

SQL> select sequence#,first_change#,next_change# from v$log_history;

SEQUENCE# FIRST_CHANGE# NEXT_CHANGE#

---------- ------------- ------------

1 446075 451208

2 451208 483347

3 483347 485272

4 485272 485277

5 485277 486119

.....

83 1227667 1229252

84 1229252 1252272

85 1252272 1252277

86 1252277 1252293

87 1252293 1252294

88 1252294 1253301

1 1255061 1255062

--sequence# 重新开始了，但是SCN 还是继续增加的。

2 1255062 1257639

3 1257639 1257644

4 1257644 1265602

5 1265602 1265607

6 1265607 1265913

94 rows selected.

SQL>

所以，这种情况下，查看同步情况还是有点不直观。 但是V$LOG_HISTORY 和V$ARCHIVED_LOG显示的log 历史信息是从控制文件中取得的，所以说，如果要删除以前的记录，只有重建控制文件了。

（3）重建控制文件

SQL> shutdown immediate

SQL> startup nomount;

SQL>create controlfile reuse database dave noresetlogs archivelog

LOGFILE

GROUP 1 '/u01/app/oracle/oradata/dave/redo01.log',

GROUP 2 '/u01/app/oracle/oradata/dave/redo02.log',

GROUP 3 '/u01/app/oracle/oradata/dave/redo03.log'

DATAFILE

'/u01/app/oracle/oradata/dave/sysaux01.dbf',

'/u01/app/oracle/oradata/dave/system01.dbf',

'/u01/app/oracle/oradata/dave/undotbs01.dbf',

'/u01/app/oracle/oradata/dave/users01.dbf'

CHARACTER SET ZHS16GBK;

--注意，使用的是noresetlogs，如果使用resetlogs，DG 就需要重新搭建了。

SQL> ALTER TABLESPACE TEMP ADD TEMPFILE '/u01/app/oracle/oradata/dave/temp01.dbf' size 100M;

Tablespace altered.

--添加临时表空间，在重建控制文件的时候，不能添加TEMP表空间，只能在控制文件重建好之后，在添加temp 表空间。

更多信息参考：

Oracle 控制文件

http://blog.csdn.net/tianlesoftware/archive/2009/12/09/4974440.aspx

（4）在次验证归档信息

主库：

SQL> select max(sequence#) from v$archived_log;

MAX(SEQUENCE#)

--------------

9

SQL> alter system switch logfile;

System altered.

SQL> select max(sequence#) from v$archived_log;

MAX(SEQUENCE#)

--------------

10

SQL> select sequence#,applied from v$archived_log;

SEQUENCE# APP

---------- ---

8 NO

7 NO

9 NO

9 YES

10 YES

10 NO

6 rows selected.

SQL> select sequence#,first_change#,next_change# from v$log_history;

SEQUENCE# FIRST_CHANGE# NEXT_CHANGE#

---------- ------------- ------------

9 1267828 1268212

10 1268212 1274690

从这个结果来看，重建控制文件之后，之前的所有的有关归档的信息都会被删除。

备库：

SQL> select max(sequence#) from v$archived_log;

MAX(SEQUENCE#)

--------------

10

SQL> select sequence#,applied from v$archived_log;

SEQUENCE# APP

---------- ---

3 YES

2 YES

5 YES

4 YES

6 YES

7 YES

8 YES

9 YES

10 YES

9 rows selected.

说明：

我这里是测试环境，所以重建控制文件测试一下，如果是生产环境，小心操作。

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