如何利用閃回資料庫特性恢復failover 後的dataguard 環境?
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概述:
11204 單機對單機實施dg,因局方要求需要(讀寫模式)開啟standby ;而這時原生產環境不能有任何影響動,依然對外服務;
採用的思路是:standby 直接failover 為primary db;這時原有dg關係被破壞,互不影響;
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思路概要:
1.確認主庫歸檔日誌存放空間是否足夠?(需考慮歸檔保留刪除策略?);關閉主庫到備庫的日誌傳輸
2.備庫確認是否開啟flashback database,以及閃回日誌存放空間是否充足?
3.備庫failover to primary (切換前確認是否日誌延遲傳輸?手工註冊)
4.業務測試
5.恢復failover 備庫
6.確認dg 環境恢復是否正常(日誌自動傳輸和應用?)?
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具體實施步驟:
------主庫defer 日誌傳輸
alter system set log_archive_dest_2=defer;
---enable 日誌傳輸:
alter system set log_archive_dest_2=enable;
-----備庫(mount)配置 flashback database:
STANDBY DATABASE: Stop redo apply, configure flashback retention,
start flashback database, open the database and start redo apply (Is active DG).
---檢查備庫是否啟用flashback database:
select flashback_on from v$database;
注意這裡需要確認下備庫開啟模式: mount?readonly with apply?
在11g 環境下備庫可能啟用了 ADG 特性 備庫日誌處於實時應用,資料庫模式為 readonly with apply
這時需要重啟資料庫到mount狀態修改flashback database 模式;
如果備庫處於mount 狀態,可以先取消日誌apply ,直接開啟閃回資料庫特性;
---取消備庫日誌應用:
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
---需要配置一下兩個引數來開啟flashback database 特性:
ALTER SYSTEM SET db_recover_file_dest='/lixora/lixora/lixora/';
ALTER SYSTEM SET db_recover_file_dest_size=100G;
ALTER SYSTEM SET DB_FLASHBACK_RETENTION_TARGET=240; ---4hours
ALTER DATABASE FLASHBACK ON;
--手工建立還原點(該步驟沒有測試過):
Creating Restore point in Physical Standby:
CREATE RESTORE POINT before_damage GUARANTEE FLASHBACK DATABASE
-------備庫failover to primary db 應急切換步驟:
(注:模擬主庫由於故障無法正常switchover,需要執行failover,強制備庫->pridb並接管業務)
1.備庫:
由於是failover,所以理解主庫這時候已經無法正常使用,只需備庫切換至pridb
【前提主庫還是可用的:可選】查詢沒有應用的日誌:
SELECT THREAD#, LOW_SEQUENCE#, HIGH_SEQUENCE# FROM V$ARCHIVE_GAP;
select distinct thread#,max(sequence#) over(partition by thread#) a from v$archived_log;
該語句取得當前資料庫各執行緒已歸檔檔案最大序號,如果primary 與standby 最大序號不相同,
必須將多出的序號對應的歸檔檔案複製到待轉換的standby伺服器。
Cp過來並register
ALTER DATABASE REGISTER PHYSICAL LOGFILE 'filespec1'
停止應用恢復模式
alter database recover managed standby database finish;
or
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE FINISH FORCE;
轉換standbydb為primary db
alter database commit to switchover to primary;
重啟資料庫,恢復正常業務
alter database open;
資料庫角色檢視:
select open_mode,database_role from v$database;
OPEN_MODE DATABASE_ROLE
---------- ----------------
OPEN PRIMARY
------恢復failover 的備庫:
C. Using SQL*PLUS
Step 1 Determine the Standby Became Primary SCN.
Step 2 Flashback the Failed Primary Database.
Step 3 Convert to physical standby database.
Step 4 Restart Redo Transport.
Step 5 Start Redo Apply.
Step 1 Determine the SCN at which the old standby database became the primary database.
SQL> SELECT TO_CHAR(STANDBY_BECAME_PRIMARY_SCN) FROM V$DATABASE;
Step 2 Flashback the Failed Primary Database to SCN standby_became_primary_scn.
SQL> SHUTDOWN IMMEDIATE;
SQL> startup mount
SQL> FLASHBACK DATABASE TO SCN <standby_became_primary_scn of step 1>;
Step 3 Convert the database to a physical standby database and Restart database in mount stage.
SQL> ALTER DATABASE CONVERT TO PHYSICAL STANDBY;
SQL> SHUTDOWN IMMEDIATE;
SQL> STARTUP MOUNT;
Step 4 Restart Redo Transport to the New Physical Standby Database.
1. If you have not set the remote archive destination on current primary then set remote archive destination:
SQL>ALTER SYSTEM SET LOG_ARCHIVE_DEST_2 = 'SERVICE=lixora VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=lixora' SCOPE=BOTH;
2. Enable the destination
SQL>ALTER SYSTEM SET LOG_ARCHIVE_DEST_STATE_2=ENABLE;
3. Perform a log switch to ensure that standby database begins receiving redo data from the new primary database
SQL> ALTER SYSTEM SWITCH LOGFILE;
SQL> SELECT DEST_ID, STATUS, ERROR FROM V$ARCHIVE_DEST WHERE DEST_ID=2;
--確認日誌是否都apply了?
select applied from v$archived_log;
select message from v$dataguard_status;
Step 5 Start Redo Apply.
SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION;
Please see also fallowing docu:
TIPS:
Oracle? Data Guard Concepts and Administration
11g Release 2 (11.2)
13.2 Converting a Failed Primary Into a Standby Database Using Flashback Database