ANBOB™

今天看老杨blog，提出了11GR2的新特性，延迟段创建 ，就是说从11GR2开始默认创建的表不会立及分配segment，不会占用磁盘空间，这听上去也是很合理的，当第一条数据insert时才会分配空间

试验一把

sys@ANBOB> conn anbob/anbob
Connected.
anbob@ANBOB> select * from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

anbob@ANBOB> create table testnew(id int primary key,name varchar2(10));

Table created.
anbob@ANBOB> create table testnew_IME(id int primary key,name varchar2(10)) segment creation immediate;

Table created.
anbob@ANBOB> create table testnew_def(id int primary key,name varchar2(10)) segment creation deferred;

Table created.

anbob@ANBOB> select segment_name from user_segments where segment_name like 'TESTNEW%';

SEGMENT_NAME
---------------------------------------------------------------------------------
TESTNEW_IME

anbob@ANBOB>  select INDEX_NAME,TABLE_OWNER from USER_indexes where table_name='TESTNEW';

INDEX_NAME                     TABLE_OWNER
------------------------------ ------------------------------
SYS_C0010903                   ANBOB
anbob@ANBOB>  select INDEX_NAME,TABLE_OWNER from USER_indexes where table_name='TESTNEW_IME';

INDEX_NAME                     TABLE_OWNER
------------------------------ ------------------------------
SYS_C0010904                   ANBOB
anbob@ANBOB>  select INDEX_NAME,TABLE_OWNER from USER_indexes where table_name='TESTNEW_DEF';

INDEX_NAME                     TABLE_OWNER
------------------------------ ------------------------------
SYS_C0010905                   ANBOB

anbob@ANBOB> select segment_name from user_segments where segment_name='SYS_C0010903';

no rows selected

anbob@ANBOB> select segment_name from user_segments where segment_name='SYS_C0010904';

SEGMENT_NAME
---------------------------------------------------------------------------------
SYS_C0010904
anbob@ANBOB> select segment_name from user_segments where segment_name='SYS_C0010905';

no rows selected


anbob@ANBOB> insert into testnew values(1,'anbob.com');

1 row created.

anbob@ANBOB> commit;

Commit complete.

anbob@ANBOB> select segment_name from user_segments where segment_name like 'TESTNEW%';

SEGMENT_NAME
---------------------------------------------------------------------------------
TESTNEW
TESTNEW_IME

anbob@ANBOB>  select INDEX_NAME,TABLE_OWNER from USER_indexes where table_name='TESTNEW';

INDEX_NAME                     TABLE_OWNER
------------------------------ ------------------------------
SYS_C0010903                   ANBOB

anbob@ANBOB> select segment_name from user_segments where segment_name='SYS_C0010903';

SEGMENT_NAME
---------------------------------------------------------------------------------
SYS_C0010903
anbob@ANBOB> truncate table testnew;

Table truncated.

anbob@ANBOB> select segment_name from user_segments where segment_name like 'TESTNEW%';

SEGMENT_NAME
---------------------------------------------------------------------------------
TESTNEW
TESTNEW_IME
anbob@ANBOB> conn sys/oracle as sysdba
Connected.
sys@ANBOB> create table testnew_def(id int primary key,name varchar2(10)) segment creation deferred;
create table testnew_def(id int primary key,name varchar2(10)) segment creation deferred
*
ERROR at line 1:
ORA-14223: 此表不支持延迟创建段

note:
11g r2默认是使用segment creation deferred建立，新建的无记录表不分配sement,当insert 第一条记录时分配段空间，不会因truncate而回收，并且在sys schema里不支持,听说exp 也不会导出

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