逻辑备库与物理备库不同，它并不是Primary数据库的一个精确的copy。同一rowid，在逻辑备库上返回的值并不是相同的。有些数据类型或者对象，逻辑备库并不支持同步。在创建逻辑备库之前，你首先要确认，哪些schema及对象是不被SQL-APPLY支持的。
1. 查询不被同步的schema 。
SQL> set pagesize 200 SQL> SELECT OWNER FROM DBA_LOGSTDBY_SKIP WHERE STATEMENT_OPT = ‘INTERNAL SCHEMA‘; OWNER ------------------------------- SYS SYSTEM OUTLN MGMT_VIEW MDSYS ORDSYS EXFSYS DBSNMP WMSYS APPQOSSYS APEX_030200 ORDDATA CTXSYS ANONYMOUS SYSMAN XDB ORDPLUGINS OWBSYS SI_INFORMTN_SCHEMA OLAPSYS ORACLE_OCM XS$NULL DIP 23 rows selected.
2. 查询哪些表是不被执行的。
SQL> SELECT DISTINCT OWNER,TABLE_NAME FROM DBA_LOGSTDBY_UNSUPPORTED ORDER BY OWNER,TABLE_NAME; no rows selected
3. 如果上步返回数据，可以通过如下查询得知是哪些类型不被支持
SQL> SELECT COLUMN_NAME,DATA_TYPE FROM DBA_LOGSTDBY_UNSUPPORTED WHERE OWNER=‘OE‘ AND TABLE_NAME = ‘CUSTOMERS‘; no rows selected
4. 逻辑备库的SQL-APPLY是通过表的唯一标识进行的，也就是说表必须有主键或者唯一性索引。
SQL> col owner for a10 SQL> col table_name for a30 SQL> SELECT OWNER, TABLE_NAME FROM DBA_LOGSTDBY_NOT_UNIQUE; OWNER TABLE_NAME ---------- ------------------------------ SCOTT BONUS SCOTT SALGRADE SCOTT T1
如果表没有主键或唯一约束怎么办？Oracle会在日志文件中写入supplemental logging 。也就是会写入大量的附加信息，用所有的column的值以构建update时的唯一性。
当然也有一些表是无法构建唯一性的，可以通过如下语句查询
SELECT OWNER, TABLE_NAME FROM DBA_LOGSTDBY_NOT_UNIQUE WHERE (OWNER, TABLE_NAME) NOT IN (SELECT DISTINCT OWNER, TABLE_NAME FROM DBA_LOGSTDBY_UNSUPPORTED) AND BAD_COLUMN = ‘Y‘;
5. 关闭物理备库的日志应用
SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL; Database altered.
6. 构建创建逻辑备库必要的数据字典。
转到主库上执行如下命令
SQL> EXECUTE DBMS_LOGSTDBY.BUILD; PL/SQL procedure successfully completed.
此命令做了如下事情
主库上开启supplemental logging功能。
在主库上构建LogMiner的数据字典，使得逻辑备库知道如何处理主库发来的redo数据。
记录一个scn号，从库上的SQL-APPLY方式日志应用从此scn号开始。
7. 如果有主备切换的需求，那么必须先在standby数据库上手工开启supplemental logging。
SQL> ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (PRIMARY KEY, UNIQUE INDEX) COLUMNS; Database altered.
8. 在从库上应用切换成逻辑备库之前的redo
SQL> ALTER DATABASE RECOVER TO LOGICAL STANDBY "standby"; ALTER DATABASE RECOVER TO LOGICAL STANDBY "standby" * ERROR at line 1: ORA-19953: database should not be open SQL> shutdown immediate Database closed. Database dismounted. ORACLE instance shut down. SQL> startup mount ORACLE instance started. Total System Global Area 839282688 bytes Fixed Size 2233000 bytes Variable Size 494931288 bytes Database Buffers 339738624 bytes Redo Buffers 2379776 bytes Database mounted. SQL> ALTER DATABASE RECOVER TO LOGICAL STANDBY "standby"; Database altered.
9. 打开数据库
SQL> shutdown immediate ORA-01507: database not mounted ORACLE instance shut down. SQL> startup mount ORACLE instance started. Total System Global Area 839282688 bytes Fixed Size 2233000 bytes Variable Size 494931288 bytes Database Buffers 339738624 bytes Redo Buffers 2379776 bytes Database mounted. SQL> alter database open resetlogs; Database altered. SQL>
10. 启动日志应该
SQL> ALTER DATABASE START LOGICAL STANDBY APPLY IMMEDIATE; Database altered.
11. 验证数据同步
主库
SQL> conn scott/tiger Connected. SQL> select count(*) from t1; COUNT(*) ---------- 14 SQL> insert into t1 select * from t1; 14 rows created. SQL> commit; Commit complete.
从库上查询数据
SQL> conn scott/tiger Connected. SQL> select count(*) from t1; COUNT(*) ---------- 28
从库也能建立表，修改数据等。
SQL> conn / as sysdba Connected. SQL> ALTER DATABASE STOP LOGICAL STANDBY APPLY; Database altered. SQL> ALTER SESSION DISABLE GUARD; Session altered. SQL> create table scott.t2 as select * from scott.t1; Table created. SQL> ALTER SESSION ENABLE GUARD; Session altered. SQL> ALTER DATABASE START LOGICAL STANDBY APPLY IMMEDIATE; Database altered.
SQL> conn / as sysdba Connected. SQL> ALTER SESSION DISABLE GUARD; Session altered. SQL> insert into scott.t1 select * from scott.t1; 28 rows created. SQL> commit; Commit complete. SQL> alter session enable guard; Session altered.
被DataGuard传输的表，也能被修改数据，这个还蛮危险的，两边的数据就不一致啦。
本文出自 “叮咚” 博客，请务必保留此出处http://lqding.blog.51cto.com/9123978/1682704
Oracle学习之DATAGUARD(五) 创建logic standby
原文地址：http://lqding.blog.51cto.com/9123978/1682704
