这段时间在做数据迁移,需要从10g的ZHS16GBK字符集的数据库里面迁移数据到11g的UTF8字符的数据库,并且源数据库的NLS_LENGTH_SEMANTICS参数值为Byte,目标端的NLS_LENGTH_SEMANTICS参数值为CHAR。如果直接从源使用exp/expdp导出数据,然后使用imp/impdp导入数据到目标的话,可能会出现数据超长的情况,这时候就不好搞了,因此我就使用了中转的方式。即,把源数据导入到NLS_LENGTH_SEMANTICS参数值为CHAR的ZHS16GBK字符集的中转数据库中,然后再从中转数据库中导出数据并导入到目标数据库中。
注:这样做是有条件的,源数据库中没有长度超过4000/3个中文字符的CHAR/VARCHAR2字段,原因看这里
继续这个问题,之所以这么做,目的是为了在数据部超长的情况得到CHAR/VARCHAR2类型字段以CHAR存储的数据。
根据Oracle的定义,NLS_LENGTH_SEMANTICS参数可以在三个层次生效:数据库级、实例级、会话级,并且生效的优先顺序为会话级>实例级>数据库级。
但是,我发现了一个问题:不管把NLS_LENGTH_SEMANTICS在那个级别设置为CHAR,在Oracle 11.2.0.1中,新导入表都不会使用CHAR做为CHAR/VARCHAR2等数据类型的存储单位,而是一律使用默认的Byte,除非源数据就已经指定了CHAR。
请看如下实验过程,全过程均使用普通用户,因为NLS_LENGTH_SEMANTICS参数对sys用户无效:
先查看NLS_LENGTH_SEMANTICS参数,Database、Instance和Session都设置为CHAR
srcbdb@SYS> select * from nls_session_parameters where PARAMETER='NLS_LENGTH_SEMANTICS';
PARAMETER VALUE
------------------------------ --------------------------------------------------
NLS_LENGTH_SEMANTICS CHAR
srcbdb@SYS> select * from nls_instance_parameters where PARAMETER='NLS_LENGTH_SEMANTICS';
PARAMETER VALUE
------------------------------ --------------------------------------------------
NLS_LENGTH_SEMANTICS CHAR
srcbdb@SYS> select * from nls_database_parameters where PARAMETER='NLS_LENGTH_SEMANTICS';
PARAMETER VALUE
------------------------------ --------------------------------------------------
NLS_LENGTH_SEMANTICS CHAR
然后倒入数据
[oracle@instsvr1 dumpdp]$ impdp vip/vip directory=dumpdir dumpfile=vip.byte.dat logfile=$ORACLE_SID.vip.impdp.`date +'%Y%m%d%H%M%S'`.log
Import: Release 11.2.0.1.0 - Production on Wed Mar 7 16:21:03 2012
Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Data Mining
and Real Application Testing options
Master table "VIP"."SYS_IMPORT_FULL_01" successfully loaded/unloaded
Starting "VIP"."SYS_IMPORT_FULL_01": vip/******** directory=dumpdir dumpfile=vip.byte.dat logfile=srcbdb.vip.impdp.20120307162103.log
Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
Processing object type SCHEMA_EXPORT/DB_LINK
ORA-31685: Object type DB_LINK:"VIP"."DB_SRCBDATA" failed due to insufficient privileges. Failing sql is:
CREATE DATABASE LINK "DB_SRCBDATA" CONNECT TO "SRCBDATA" IDENTIFIED BY VALUES '053E86648883623A93807EAD3C7A2EA776FA8F916A941AFB2E' USING 'srcbfin'
Processing object type SCHEMA_EXPORT/SEQUENCE/SEQUENCE
Processing object type SCHEMA_EXPORT/TABLE/TABLE
Processing object type SCHEMA_EXPORT/TABLE/GRANT/OWNER_GRANT/OBJECT_GRANT
Processing object type SCHEMA_EXPORT/TABLE/INDEX/INDEX
Processing object type SCHEMA_EXPORT/TABLE/CONSTRAINT/CONSTRAINT
Processing object type SCHEMA_EXPORT/TABLE/INDEX/STATISTICS/INDEX_STATISTICS
Processing object type SCHEMA_EXPORT/TABLE/COMMENT
Processing object type SCHEMA_EXPORT/FUNCTION/FUNCTION
Processing object type SCHEMA_EXPORT/PROCEDURE/PROCEDURE
Processing object type SCHEMA_EXPORT/FUNCTION/ALTER_FUNCTION
Processing object type SCHEMA_EXPORT/PROCEDURE/ALTER_PROCEDURE
Processing object type SCHEMA_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
Job "VIP"."SYS_IMPORT_FULL_01" completed with 1 error(s) at 16:24:48
查看表结构
[oracle@instsvr1 dumpdp]$ sqlplus vip/vip
SQL*Plus: Release 11.2.0.1.0 Production on Wed Mar 7 14:56:04 2012
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Data Mining
and Real Application Testing options
srcbdb@VIP> select * from tab where rownum <10;
TNAME TABTYPE CLUSTERID
------------------------------------------------------------ -------------- ----------
DISCARD_TBDSCLIENT TABLE
IT_AJDK TABLE
IT_DSDK TABLE
IT_DSDQCK TABLE
IT_DSHQCK TABLE
IT_DSKH TABLE
SNAPTBEXCHANGERATE TABLE
TBADVICELOG TABLE
TBADVICELOGSETMEAL TABLE
9 rows selected.
srcbdb@VIP> desc SNAPTBEXCHANGERATE
Name Null? Type
----------------------------------------------------------------------------------------------------------------- -------- ----------------------------------------------------------------------------
MONEY_TYPE VARCHAR2(3) <-------------- 这说明表是以Byte存储VARCHAR2数据类型的。
TO_RMB_RATE NUMBER(15,7)
TO_USD_RATE NUMBER(15,7)
我们再新建一个表看一下,注意,不显示指定CHAR或者Byte,数据使用默认值!
结论:在11.2.0.1里面,对于使用imp/impdp工具导入的数据,nls_length_semantics不生效!
我不知道这是不是Oracle的Bug,看官也可以帮我求证一下!!!!
【附录:MOS上的文章】
Examples and limits of BYTE and CHAR semantics usage (NLS_LENGTH_SEMANTICS) [ID 144808.1]