读写分离（实时查询standby）
备用数据库一边进行日志恢复，一边对外提供服务，如果在加上最大保护模式，用户在备用数据库上就能查看到准确的实时数据了。
先确认备库的状态
| SQL> select NAME ,OPEN_MODE, PROTECTION_MODE ,PROTECTION_LEVEL, REMOTE_ARCHIVE, DATABASE_ROLE, SWITCHOVER_STATUS from v$database;
NAME OPEN_MODE PROTECTION_MODE PROTECTION_LEVEL --------- -------------------- -------------------- -------------------- REMOTE_A DATABASE_ROLE SWITCHOVER_STATUS -------- ---------------- -------------------- ORCL MOUNTED MAXIMUM PERFORMANCE MAXIMUM PERFORMANCE ENABLED PHYSICAL STANDBY NOT ALLOWED |
进入只读状态
| SQL> alter database recover managed standby database cancel;
Database altered.
SQL> alter database open;
Database altered.
SQL> select NAME ,OPEN_MODE, PROTECTION_MODE ,PROTECTION_LEVEL, REMOTE_ARCHIVE, DATABASE_ROLE, SWITCHOVER_STATUS from v$database;
NAME OPEN_MODE PROTECTION_MODE PROTECTION_LEVEL --------- -------------------- -------------------- -------------------- REMOTE_A DATABASE_ROLE SWITCHOVER_STATUS -------- ---------------- -------------------- ORCL READ ONLY MAXIMUM PERFORMANCE MAXIMUM PERFORMANCE ENABLED PHYSICAL STANDBY NOT ALLOWED |
再次启动数据库的恢复
| SQL> alter database recover managed standby database disconnect from session;
Database altered.
SQL> select NAME ,OPEN_MODE, PROTECTION_MODE ,PROTECTION_LEVEL, REMOTE_ARCHIVE, DATABASE_ROLE, SWITCHOVER_STATUS from v$database;
NAME OPEN_MODE PROTECTION_MODE PROTECTION_LEVEL --------- -------------------- -------------------- -------------------- REMOTE_A DATABASE_ROLE SWITCHOVER_STATUS -------- ---------------- -------------------- ORCL READ ONLY WITH APPLY MAXIMUM PERFORMANCE MAXIMUM PERFORMANCE ENABLED PHYSICAL STANDBY NOT ALLOWED |
现在备库的状态现在是read only with apply.
现在在主库上做一下操作
| SQL> create table test (id number);
Table created.
SQL> alter system switch logfile;
System altered. |
现在去查备库是看不到test这个表的，做几次日志切换就能在备库看到test表了。
| SQL> select * from test; select * from test * ERROR at line 1: ORA-00942: table or view does not exist
SQL> /
no rows selected |
可见主库上的变化已经映射到备库了，因为目前还不是实时恢复的，使用实时恢复，这个时候，必须有standby log
| SQL> select * from v$logfile;
GROUP# STATUS TYPE MEMBER IS_ ---------- ------- ------- ---------------------------------------------------------------------- --- 3 ONLINE /u01/app/oracle/oradata/std/redo03.log NO 2 ONLINE /u01/app/oracle/oradata/std/redo02.log NO 1 ONLINE /u01/app/oracle/oradata/std/redo01.log NO 4 STANDBY /u01/app/oracle/fast_recovery_area/STD/onlinelog/o1_mf_4_9kof4jt9_.log YES 5 STANDBY /u01/app/oracle/fast_recovery_area/STD/onlinelog/o1_mf_5_9kof4m2w_.log YES 6 STANDBY /u01/app/oracle/fast_recovery_area/STD/onlinelog/o1_mf_6_9kof4n53_.log YES 7 STANDBY /u01/app/oracle/fast_recovery_area/STD/onlinelog/o1_mf_7_9kof4nyc_.log YES |
再次取消recover，重新使用实时恢复。
| SQL> alter database recover managed standby database using current logfile disconnect from session;
Database altered.
SQL> select NAME ,OPEN_MODE, PROTECTION_MODE ,PROTECTION_LEVEL, REMOTE_ARCHIVE, DATABASE_ROLE, SWITCHOVER_STATUS from v$database;
NAME OPEN_MODE PROTECTION_MODE PROTECTION_LEVEL --------- -------------------- -------------------- -------------------- REMOTE_A DATABASE_ROLE SWITCHOVER_STATUS -------- ---------------- -------------------- ORCL READ ONLY WITH APPLY MAXIMUM PERFORMANCE MAXIMUM PERFORMANCE ENABLED PHYSICAL STANDBY NOT ALLOWED |
主库上插入
| SQL> insert into test values (1);
1 row created.
SQL> insert into test values (2);
1 row created.
SQL> commit 2 ;
Commit complete. |
在备库立马就可以看到
| SQL> select * from test;
ID ---------- 1 2 |