1.三种保护模式

– Maximum protection

在Maximum protection下， 可以保证从库和主库数据完全一样，做到zero data loss.事务同时在主从两边提交完成，才算事务完成。如果从库宕机或者网络出现问题，主从库不能通讯，主库也立即宕机。在这种方式下，具有最高的保护等级。但是这种模式对主库性能影响很大，要求高速的网络连接。

– Maximum availability

在Maximum availability模式下，如果和从库的连接正常，运行方式等同Maximum protection模式，事务也是主从库同时提交。如果从库和主库失去联系，则主库自动切换到Maximum performance模式下运行，保证主库具有最大的可用性。

– Maximum performance

在Maximum performance，主库把归档的 archived log通过arch进程传递给从库，在这种方式下，主库运行性能最高，但是不能保证数据不丢失，且丢失的数据受redo log的大小影响。在redo log过大的情况下，可能一天都没有归档一个日志，可以通过手工切换日志的方式来减小数据的丢失。

2.模式切换(Maximum performance切换至Maximum availability)

a.查看保护的模式

DGbroker查看：

DGMGRL> show configuration verbose;

Configuration - dgc

Protection Mode: MaxPerformance

Databases:

atest1 - Primary database

atest2 - Physical standby database

Properties:

FastStartFailoverThreshold = '30'

OperationTimeout = '30'

FastStartFailoverLagLimit = '30'

CommunicationTimeout = '180'

ObserverReconnect = '0'

FastStartFailoverAutoReinstate = 'TRUE'

FastStartFailoverPmyShutdown = 'TRUE'

BystandersFollowRoleChange = 'ALL'

ObserverOverride = 'FALSE'

ExternalDestination1 = ''

ExternalDestination2 = ''

PrimaryLostWriteAction = 'CONTINUE'

Fast-Start Failover: DISABLED

Configuration Status:

SUCCESS

sqlplus查看：

SQL> select database_role,protection_mode,protection_level from v$database;

DATABASE_ROLE PROTECTION_MODE PROTECTION_LEVEL

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

PRIMARY MAXIMUM PERFORMANCE MAXIMUM PERFORMANCE

b.查看备库的日志传输模式(参数LogXptMode(sync:同步传输/async:异步传输))

DGMGRL> show database verbose 'atest2';

Database - atest2

Role: PHYSICAL STANDBY

Intended State: APPLY-ON

Transport Lag: 0 seconds (computed 1 second ago)

Apply Lag: 0 seconds (computed 1 second ago)

Apply Rate: 97.00 KByte/s

Real Time Query: ON

Instance(s):

atest

Properties:

DGConnectIdentifier = 'atest2'

ObserverConnectIdentifier = ''

LogXptMode = 'sync'

DelayMins = '0'

Binding = 'optional'

MaxFailure = '0'

MaxConnections = '1'

ReopenSecs = '300'

NetTimeout = '30'

RedoCompression = 'DISABLE'

LogShipping = 'ON'

PreferredApplyInstance = ''

ApplyInstanceTimeout = '0'

ApplyParallel = 'AUTO'

StandbyFileManagement = 'AUTO'

ArchiveLagTarget = '0'

LogArchiveMaxProcesses = '4'

LogArchiveMinSucceedDest = '1'

DbFileNameConvert = ''

LogFileNameConvert = ''

FastStartFailoverTarget = ''

InconsistentProperties = '(monitor)'

InconsistentLogXptProps = '(monitor)'

SendQEntries = '(monitor)'

LogXptStatus = '(monitor)'

RecvQEntries = '(monitor)'

ApplyLagThreshold = '0'

TransportLagThreshold = '0'

TransportDisconnectedThreshold = '30'

SidName = 'atest'

StaticConnectIdentifier = '(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=vijay02.database.com)(PORT=1521))(CONNECT_DATA=(SERVICE_NAME=atest2_DGMGRL)(INSTANCE_NAME=atest)(SERVER=DEDICATED)))'

StandbyArchiveLocation = '/u01/app/oracle/oradata/ATEST/archivelog'

AlternateLocation = ''

LogArchiveTrace = '0'

LogArchiveFormat = '%t_%s_%r.dbf'

TopWaitEvents = '(monitor)'

Database Status:

SUCCESS

c.如果LogXptMode的值为async，就要将其修改为sync

DGMGRL> edit database atest1 set property logxptmode=sync;

Property "logxptmode" updated

d.修改完之后再次确认LogXptMode的值，如步骤b

e.切换模式(如果切换失败，则再次去确认备库LogXptMode的值)

DGMGRL> edit configuration set protection mode as maxavailability;

Succeeded.

f. 确认数据库的的保护模式，如步骤a

g.需要注意的是，步骤c中修改的sync是备库的值，切记！

3.个人小结：

a.三种模式在可以在DGbroker中自由切换(使用步骤2的方式)(在测试库中)，正常情况下，数据库能迅速反应过来(查看保护模式的时候)。

b.使用Maximum performance的时候，参数(备库)LogXptMode设置为async就好/

c.使用Maximum protection或者Maximum availability的时候，参数(备库)LogXptMode要设置为sync。

d.(经测试)使用Maximum protection时，当备库出现异常(如网络问题，数据库宕机)，主库会挂起(告警日志会报如下错误)，当备库恢复正常之后，主库也会恢复。

LGWR: Error 1034 attaching to RFS for reconnect

e.使用Maximum protection时，在当备库出现异常的情况下，当主库挂起时，(主库)可以强制切换到 Maximum performance，但当重新切回Maximum protection(在备库恢复时)，主库需重启。

DGMGRL> edit configuration set protection mode as maxprotection;

Operation requires shutdown of instance "atest" on database "atest1"

Shutting down instance "atest"...

Unable to connect to database

ORA-12545: Connect failed because target host or object does not exist

Failed.

Warning: You are no longer connected to ORACLE.

Please complete the following steps to finish the operation:

shut down instance "atest" of database "atest1"

start up instance "atest" of database "atest1"

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