表的storage (MINEXTENTS 属性对truncate后表大小的影响
TRUNCATE表后对表大小进行查询，表的空间没有释放完毕？
对此进行实验测试，结果如下：(测试环境LINUX+ORACLE11.2.0.3)
创建表时语句指定了storage (MINEXTENTS 5);时，TRUNCATE后还有5个EXTENT；
创建表时语句不指定storage (MINEXTENTS参数，即使用默认值时；TRUNCATE后只有1个EXTENT；
------------ 实验1：指定了storage (MINEXTENTS 5)
实验2：创建表时不指定storage (MINEXTENTS参数 使用默认值
对此进行实验测试，结果如下：(测试环境LINUX+ORACLE11.2.0.3)
创建表时语句指定了storage (MINEXTENTS 5);时，TRUNCATE后还有5个EXTENT；
创建表时语句不指定storage (MINEXTENTS参数，即使用默认值时；TRUNCATE后只有1个EXTENT；
------------ 实验1：指定了storage (MINEXTENTS 5)
SQL> create tablespace test2 datafile '/u01/oracle/base/oracle/oradata/bys7/test2.dbf' size 10m uniform size 40k; Tablespace created. SQL> show user USER is "TEST" SQL> create table test1(aa number,name varchar2(128)) tablespace test2 storage (MINEXTENTS 5); Table created. SQL> select owner,SEGMENT_NAME,TABLESPACE_NAME,EXTENT_ID from dba_extents where SEGMENT_NAME='TEST1'; OWNER SEGMENT_NAME TABLESPACE_NAME EXTENT_ID ------------------------------ ------------ --------------- ---------- TEST TEST1 TEST2 0 TEST TEST1 TEST2 1 TEST TEST1 TEST2 2 TEST TEST1 TEST2 3 TEST TEST1 TEST2 4 SQL> insert into test1 select object_id,object_name from dba_objects; 13723 rows created. SQL> commit; Commit complete. SQL> select owner,SEGMENT_NAME,TABLESPACE_NAME,EXTENT_ID from dba_extents where SEGMENT_NAME='TEST1'; OWNER SEGMENT_NAME TABLESPACE_NAME EXTENT_ID ------------------------------ ------------ --------------- ---------- TEST TEST1 TEST2 0 TEST TEST1 TEST2 1 TEST TEST1 TEST2 2 TEST TEST1 TEST2 3 TEST TEST1 TEST2 4 TEST TEST1 TEST2 5 TEST TEST1 TEST2 6 TEST TEST1 TEST2 7 TEST TEST1 TEST2 8 TEST TEST1 TEST2 9 TEST TEST1 TEST2 10 TEST TEST1 TEST2 11 12 rows selected. SQL>truncate table test1; Table truncated. SQL> select owner,SEGMENT_NAME,TABLESPACE_NAME,EXTENT_ID from dba_extents where SEGMENT_NAME='TEST1'; OWNER SEGMENT_NAME TABLESPACE_NAME EXTENT_ID ------------------------------ ------------ --------------- ---------- TEST TEST1 TEST2 0 TEST TEST1 TEST2 1 TEST TEST1 TEST2 2 TEST TEST1 TEST2 3 TEST TEST1 TEST2 4 SQL> select SEGMENT_NAME,TABLESPACE_NAME,BYTES/1024 kb,EXTENTS,BLOCKS,INITIAL_EXTENT,NEXT_EXTENT,MIN_EXTENTS,MAX_EXTENTS from dba_segments where SEGMENT_NAME='TEST1'; SEGMENT_NAME TABLESPACE_NAME KB EXTENTS BLOCKS INITIAL_EXTENT NEXT_EXTENT MIN_EXTENTS MAX_EXTENTS ------------ --------------- ---------- ---------- ---------- -------------- ----------- ----------- ----------- TEST1 TEST2 200 5 25 204800 40960 1 2147483645
实验2：创建表时不指定storage (MINEXTENTS参数 使用默认值
SQL> create table test2 tablespace test2 as select object_id,object_name from dba_objects; Table created. SQL> set pagesize 1000 SQL> select owner,SEGMENT_NAME,TABLESPACE_NAME,EXTENT_ID from dba_extents where SEGMENT_NAME='TEST2'; OWNER SEGMENT_NAME TABLESPACE_NAME EXTENT_ID ------------------------------ ------------ --------------- ---------- TEST TEST2 TEST2 0 TEST TEST2 TEST2 1 TEST TEST2 TEST2 2 TEST TEST2 TEST2 3 TEST TEST2 TEST2 4 TEST TEST2 TEST2 5 TEST TEST2 TEST2 6 TEST TEST2 TEST2 7 TEST TEST2 TEST2 8 TEST TEST2 TEST2 9 TEST TEST2 TEST2 10 TEST TEST2 TEST2 11 12 rows selected. SQL> truncate table test2; Table truncated. SQL> select owner,SEGMENT_NAME,TABLESPACE_NAME,EXTENT_ID from dba_extents where SEGMENT_NAME='TEST2'; OWNER SEGMENT_NAME TABLESPACE_NAME EXTENT_ID ------------------------------ ------------ --------------- ---------- TEST TEST2 TEST2 0