1.三種保護模式
– Maximum protection
在Maximum protection下, 可以保證從庫和主庫數據完全一樣,做到zero data loss.事務同時在主從兩邊提交完成,才算事務完成。如果從庫宕機或者網絡出現問題,主從庫不能通訊,主庫也立即宕機。在這種方式下,具有最高的保護等級。但是這種模式對主庫性能影響很大,要求高速的網絡連接。
– Maximum availability
在Maximum availability模式下,如果和從庫的連接正常,運行方式等同Maximum protection模式,事務也是主從庫同時提交。如果從庫和主庫失去聯系,則主庫自動切換到Maximum performance模式下運行,保證主庫具有最大的可用性。
– Maximum performance
在Maximum performance,主庫把歸檔的 archived log通過arch進程傳遞給從庫,在這種方式下,主庫運行性能最高,但是不能保證數據不丟失,且丟失的數據受redo log的大小影響。在redo log過大的情況下,可能一天都沒有歸檔一個日志,可以通過手工切換日志的方式來減小數據的丟失。
2.模式切換(Maximum performance切換至Maximum availability)
a.查看保護的模式
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.查看備庫的日志傳輸模式(參數LogXptMode(sync:同步傳輸/async:異步傳輸))
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的值為async,就要將其修改為sync
DGMGRL> edit database atest1 set property logxptmode=sync; Property "logxptmode" updated
d.修改完之後再次確認LogXptMode的值,如步驟b
e.切換模式(如果切換失敗,則再次去確認備庫LogXptMode的值)
DGMGRL> edit configuration set protection mode as maxavailability; Succeeded.
f. 確認數據庫的的保護模式,如步驟a
g.需要注意的是,步驟c中修改的sync是備庫的值,切記!
3.個人小結:
a.三種模式在可以在DGbroker中自由切換(使用步驟2的方式)(在測試庫中),正常情況下,數據庫能迅速反應過來(查看保護模式的時候)。
b.使用Maximum performance的時候,參數(備庫)LogXptMode設置為async就好/
c.使用Maximum protection或者Maximum availability的時候,參數(備庫)LogXptMode要設置為sync。
d.(經測試)使用Maximum protection時,當備庫出現異常(如網絡問題,數據庫宕機),主庫會掛起(告警日志會報如下錯誤),當備庫恢復正常之後,主庫也會恢復。
LGWR: Error 1034 attaching to RFS for reconnect
e.使用Maximum protection時,在當備庫出現異常的情況下,當主庫掛起時,(主庫)可以強制切換到 Maximum performance,但當重新切回Maximum protection(在備庫恢復時),主庫需重啟。
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"