此文将给出在使用Oracle临时表的过程中需要注意的事项,并对这些特点进行验证。
①临时表不支持物化视图
②可以在临时表上创建索引
③可以基于临时表创建视图
④临时表结构可被导出,但内容不可以被导出
⑤临时表通常是创建在用户的临时表空间中的,不同用户可以有自己的独立的临时表空间
⑥不同的session不可以互相访问对方的临时表数据
⑦临时表数据将不会上DML(Data Manipulation Language)锁
1.临时表不支持物化视图
1)环境准备
(1)创建基于会话的临时表
sec@ora10g> create global temporary table t_temp_session (x int) on commit preserve rows;
Table created.
sec@ora10g> col TABLE_NAME for a30
sec@ora10g> col TEMPORARY for a10
sec@ora10g> select TABLE_NAME,TEMPORARY from user_tables where table_name = 'T_TEMP_SESSION';
TABLE_NAME TEMPORARY
------------------------------ ----------
T_TEMP_SESSION Y
(2)初始化两条数据
sec@ora10g> insert into t_temp_session values (1);
1 row created.
sec@ora10g> insert into t_temp_session values (2);
1 row created.
sec@ora10g> commit;
Commit complete.
sec@ora10g> select * from t_temp_session;
X
----------
1
2
(3)在临时表T_TEMP_SESSION上添加主键
sec@ora10g> alter table T_TEMP_SESSION add constraint PK_T_TEMP_SESSION primary key(x);
Table altered.
2)在临时表T_TEMP_SESSION上创建物化视图
(1)创建物化视图日志日志
sec@ora10g> create materialized view log on T_TEMP_SESSION with sequence, rowid (x) including new values;
create materialized view log on T_TEMP_SESSION with sequence, rowid (x) including new values
*
ERROR at line 1:
ORA-14451: unsupported feature with temporary table
可见,在创建物化视图时便提示,临时表上无法创建物化视图日志。
(2)创建物化视图
sec@ora10g> create materialized view mv_T_TEMP_SESSION build immediate refresh fast on commit enable query rewrite as select * from T_TEMP_SESSION;
create materialized view mv_T_TEMP_SESSION build immediate refresh fast on commit enable query rewrite as select * from T_TEMP_SESSION
*
ERROR at line 1:
ORA-23413: table "SEC"."T_TEMP_SESSION" does not have a materialized view log
由于物化视图日志没有创建成功,因此显然物化视图亦无法创建。
2.在临时表上创建索引
sec@ora10g> create index i_t_temp_session on t_temp_session (x);
Index created.
临时表上索引创建成功。
3.基于临时表创建视图
sec@ora10g> create view v_t_temp_session as select * from t_temp_session where x<100;
View created.
基于临时表的视图创建成功。
4.临时表结构可被导出,但内容不可以被导出
1)使用exp工具备份临时表
ora10g@secdb /home/oracle$ exp sec/sec file=t_temp_session.dmp log=t_temp_session.log tables=t_temp_session
Export: Release 10.2.0.1.0 - Production on Wed Jun 29 22:06:43 2011
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
Export done in WE8ISO8859P1 character set and AL16UTF16 NCHAR character set
About to export specified tables via Conventional Path ...
. . exporting table T_TEMP_SESSION
Export terminated successfully without warnings.
可见在备份过程中,没有显示有数据被导出。
2)使用imp工具的show选项查看备份介质中的SQL内容
ora10g@secdb /home/oracle$ imp sec/sec file=t_temp_session.dmp full=y show=y
Import: Release 10.2.0.1.0 - Production on Wed Jun 29 22:06:57 2011
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
Export file created by EXPORT:V10.02.01 via conventional path
import done in WE8ISO8859P1 character set and AL16UTF16 NCHAR character set
. importing SEC's objects into SEC
. importing SEC's objects into SEC
"CREATE GLOBAL TEMPORARY TABLE "T_TEMP_SESSION" ("X" NUMBER(*,0)) ON COMMIT "
"PRESERVE ROWS "
"CREATE INDEX "I_T_TEMP_SESSION" ON "T_TEMP_SESSION" ("X" ) "
Import terminated successfully without warnings.
这里体现了创建临时表和索引的语句,因此临时表的结构数据是可以被导出的。
3)尝试导入数据
ora10g@secdb /home/oracle$ imp sec/sec file=t_temp_session.dmp full=y ignore=y
Import: Release 10.2.0.1.0 - Production on Wed Jun 29 22:07:16 2011
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
Export file created by EXPORT:V10.02.01 via conventional path
import done in WE8ISO8859P1 character set and AL16UTF16 NCHAR character set
. importing SEC's objects into SEC
. importing SEC's objects into SEC
Import terminated successfully without warnings.
依然显示没有记录被导入。
5.查看临时表空间的使用情况
可以通过查询V$SORT_USAGE视图获得相关信息。
sec@ora10g> select username,tablespace,session_num sid,sqladdr,sqlhash,segtype,extents,blocks from v$sort_usage;
USERNAME TABLESPACE SID SQLADDR SQLHASH SEGTYPE EXTENTS BLOCKS
-------- ---------- ------- -------- ---------- ------- ------- -------
SEC TEMP 370 389AEC58 1029988163 DATA 1 128
SEC TEMP 370 389AEC58 1029988163 INDEX 1 128
可见SEC用户中创建的临时表以及其上的索引均存放在TEMP临时表空间中。
在创建用户的时候,可以指定用户的默认临时表空间,这样不同用户在创建临时表的时候便可以使用各自的临时表空间,互不干扰。
6.不同的session不可以互相访问对方的临时表数据
1)在第一个session中查看临时表数据
sec@ora10g> select * from t_temp_session;
X
----------
1
2
此数据为初始化环境时候插入的数据。
2)在单独开启一个session,查看临时表数据。
ora10g@secdb /home/oracle$ sqlplus sec/sec
SQL*Plus: Release 10.2.0.1.0 - Production on Wed Jun 29 22:30:05 2011
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
sec@ora10g> select * from t_temp_session;
no rows selected
说明不同的session拥有各自独立的临时表操作特点,不同的session之间是不能互相访问数据。
7.临时表数据将不会上DML(Data Manipulation Language)锁
1)在新session中查看SEC用户下锁信息
sec@ora10g> col username for a8
sec@ora10g> select
2 b.username,
3 a.sid,
4 b.serial#,
5 a.type "lock type",
6 a.id1,
7 a.id2,
8 a.lmode
9 from v$lock a, v$session b
10 where a.sid=b.sid and b.username = 'SEC'
11 order by username,a.sid,serial#,a.type;
no rows selected
不存在任何锁信息。
2)向临时表中插入数据,查看锁信息
(1)插入数据
sec@ora10g> insert into t_temp_session values (1);
1 row created.
(2)查看锁信息
sec@ora10g> select
2 b.username,
3 a.sid,
4 b.serial#,
5 a.type "lock type",
6 a.id1,
7 a.id2,
8 a.lmode
9 from v$lock a, v$session b
10 where a.sid=b.sid and b.username = 'SEC'
11 order by username,a.sid,serial#,a.type;
lock lock
USERNAME SID SERIAL# type id1 id2 mode
-------- ---------- ---------- ------ ----------- ----------- ---------
SEC 142 425 TO 12125 1 3
SEC 142 425 TX 65554 446 6
此时出现TO和TX类型锁。
(3)提交数据后再次查看锁信息
sec@ora10g> commit;
Commit complete.
sec@ora10g> select
2 b.username,
3 a.sid,
4 b.serial#,
5 a.type "lock type",
6 a.id1,
7 a.id2,
8 a.lmode
9 from v$lock a, v$session b
10 where a.sid=b.sid and b.username = 'SEC'
11 order by username,a.sid,serial#,a.type;
lock lock
USERNAME SID SERIAL# type id1 id2 mode
-------- ---------- ---------- ------ ----------- ----------- ---------
SEC 142 425 TO 12125 1 3
事务所TX被释放。TO锁保留。
3)测试更新数据场景下锁信息变化
(1)更新临时表数据
sec@ora10g> update t_temp_session set x=100;
1 row updated.
(2)锁信息如下
lock lock
USERNAME SID SERIAL# type id1 id2 mode
-------- ---------- ---------- ------ ----------- ----------- ---------
SEC 142 425 TO 12125 1 3
SEC 142 425 TX 524317 464 6
(3)提交数据
sec@ora10g> commit;
Commit complete.
(4)锁信息情况
lock lock
USERNAME SID SERIAL# type id1 id2 mode
-------- ---------- ---------- ------ ----------- ----------- ---------
SEC 142 425 TO 12125 1 3
4)测试删除数据场景下锁信息变化
(1)删除临时表数据
sec@ora10g> delete from t_temp_session;
1 row deleted.
(2)查看锁信息
lock lock
USERNAME SID SERIAL# type id1 id2 mode
-------- ---------- ---------- ------ ----------- ----------- ---------
SEC 142 425 TO 12125 1 3
SEC 142 425 TX 327713 462 6
(3)提交数据
sec@ora10g> commit;
Commit complete.
(4)锁信息情况
lock lock
USERNAME SID SERIAL# type id1 id2 mode
-------- ---------- ---------- ------ ----------- ----------- ---------
SEC 142 425 TO 12125 1 3
5)总结
在临时表上的增删改等DML操作都会产生TO锁和TX事务所。TO锁会从插入数据开始一直存在。
但整个过程中都不会产生DML的TM级别锁。
8.小结
本文就临时表使用过程中常见的问题和特点进行了介绍。临时表作为Oracle的数据库对象,如果能够在理解这些特性基础上加以利用将会极大地改善系统性能。
Good luck.
secooler
11.06.29
-- The End --
当前名称:【TEMPORARYTABLE】Oracle临时表使用注意事项
URL地址:
http://cqcxhl.com/article/gjdpcg.html