[20130606]11G的表以及表空间的只读.txt

[20130606]11G的表以及表空间的只读.txt

1.只读表:
SQL> @ver
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production

SQL> create table t1 (id number);
Table created.

SQL> insert into t1 values (1);
1 row created.

SQL> commit ;
Commit complete.

SQL> alter table t1 read only ;
Table altered.

SQL> select table_name,read_only from dba_tables where wner=user and table_name='T1';
TABLE_NAME REA
---------- ---
T1         YES

SQL> insert into t1 values (2);
insert into t1 values (2)
            *
ERROR at line 1:
ORA-12081: update operation not allowed on table "SCOTT"."T1"

SQL> delete from t1 ;
delete from t1
            *
ERROR at line 1:
ORA-12081: update operation not allowed on table "SCOTT"."T1"

SQL> truncate table t1 ;
truncate table t1
               *
ERROR at line 1:
ORA-12081: update operation not allowed on table "SCOTT"."T1"

--标识的是update操作.

--drop table t1可以吗?

SQL> drop table t1;
Table dropped.
--这个跟只读表空间一样的,里面的表也可以删除.这点切记,标识表只读,依旧可以drop表.

SQL> purge table t1;
Table purged.

--这样就无法恢复了.

2.只读表空间.

--去年写过一篇,再重复测试一次.

http://space.itpub.net/267265/viewspace-745131

CREATE TABLESPACE AAA DATAFILE
  '/u01/app/oracle11g/oradata/test/aaa01.dbf' SIZE 65528K AUTOEXTEND ON NEXT 16M MAXSIZE UNLIMITED
LOGGING
ONLINE
PERMANENT
EXTENT MANAGEMENT LOCAL AUTOALLOCATE
BLOCKSIZE 8K
SEGMENT SPACE MANAGEMENT AUTO
FLASHBACK ON;

SQL> create table t1 (id number) tablespace aaa;
Table created.

SQL> insert into t1 values (1);
1 row created.

SQL> commit ;
Commit complete.

SQL> alter tablespace aaa read only;
Tablespace altered.

SQL> select tablespace_name,block_size,status from dba_tablespaces  where tablespace_name='AAA';
TABLESPACE_NAME                BLOCK_SIZE STATUS
------------------------------ ---------- ---------
AAA                                  8192 READ ONLY

SQL> insert into t1 values (2);
insert into t1 values (2)
            *
ERROR at line 1:
ORA-00372: file 11 cannot be modified at this time
ORA-01110: data file 11: '/u01/app/oracle11g/oradata/test/aaa01.dbf'

SQL> delete from t1 ;
delete from t1
            *
ERROR at line 1:
ORA-00372: file 11 cannot be modified at this time
ORA-01110: data file 11: '/u01/app/oracle11g/oradata/test/aaa01.dbf'

SQL> truncate table t1 ;
truncate table t1
               *
ERROR at line 1:
ORA-00372: file 11 cannot be modified at this time
ORA-01110: data file 11: '/u01/app/oracle11g/oradata/test/aaa01.dbf'

--能drop table吗?

SQL> drop table t1;
Table dropped.

--依旧可以删除.

SELECT owner, segment_name, segment_type, BYTES, initial_extent, next_extent, extents, max_extents, header_file, header_block
  FROM dba_segments
 WHERE tablespace_name = 'AAA';
OWNER  SEGMENT_NAME         SEGMENT_TYPE            BYTES INITIAL_EXTENT NEXT_EXTENT    EXTENTS MAX_EXTENTS HEADER_FILE HEADER_BLOCK
------ -------------------- ------------------ ---------- -------------- ----------- ---------- ----------- ----------- ------------
SCOTT  BIN$3nPoiscXV9DgQyhk TABLE                   65536          65536     1048576          1  2147483645          11          138
       qMDi8w==$0

SQL> purge table t1;
Table purged.

SELECT owner, segment_name, segment_type, BYTES, initial_extent, next_extent, extents, max_extents, header_file, header_block
  FROM dba_segments
  WHERE tablespace_name = 'AAA';
OWNER  SEGMENT_NAME         SEGMENT_TYPE            BYTES INITIAL_EXTENT NEXT_EXTENT    EXTENTS MAX_EXTENTS HEADER_FILE HEADER_BLOCK
------ -------------------- ------------------ ---------- -------------- ----------- ---------- ----------- ----------- ------------
SCOTT  11.138               TEMPORARY               65536          65536     1048576          1  2147483645          11          138

--SEGMENT_TYPE编程了TEMPORARY.

google找到一段解析:

http://blog.tanelpoder.com/2010/07/11/dropping-and-creating-tables-in-read-only-tablespaces-what/

    Wow, Oracle has converted the table segment into a temporary segment instead (see segment_type)! Bur our tablespace is
read only, how can it do that?! The answer is that neither the regular DROP nor DROP PURGE need to write anything into the
tablespace where the segment resides! The initial DROP operation just updated data dictionary, like renaming the table to
BIN$… in OBJ$ and so on. The second DROP PURGE operation just ran a bunch of deletes against data dictionary to indicate
that the table object is gone. But why is the TEMPORARY segment left behind? This has to do with locally managed tablespaces.
Before LMT days, when you dropped a segment, then the segment space was released and acquired back to tablespace through
inserts/updates to UET$/FET$ (used/free extents) base tables, which resided in system tablespace like all other data dictionary
base tables. But with LMTs, the free space information is kept in bitmaps in the tablespace files themselves! Thus, if you
drop a table in a read only LMT tablespace, the table will be gone, but the space will not be physically released (as you
can't update the LMT bitmaps in read only tablespace files). However, Oracle doesn't want to lose that space should someone
make the tablespace read write later on, so the table segment is updated to be a TEMPORARY segment instead of completely
deleting it from data dictionary. That's how the SMON can clean it up later on should that tablespace become read-write
again. The 9.130 in SEGMENT_NAME column means relative file# 9 and starting block# 130, that's a segment's unique identifier
in a tablespace. Let's move on. This example is executed on Oracle 11.2, while logged on to a non-SYS/SYSTEM user:

总结:只读表以及表空间的对象依旧可以DROP,这点切记.

时间： 2024-08-24 10:14:56

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