1、创建测试表空间
create tablespace efmis datafile '/u01/app/oracle/oradata/orcl/efmis_01.dbf' size 80m;
alter tablespace efmis add datafile '/u01/app/oracle/oradata/orcl/efmis_02.dbf' size 80m;
alter tablespace efmis add datafile '/u01/app/oracle/oradata/orcl/efmis_03.dbf' size 80m;
SQL> select t.tablespace_name,t.file_id,t.file_name,t.bytes/1024/1024/1024||'G' from dba_data_files t where t.tablespace_name='EFMIS';
TABLESPACE_NAME FILE_ID FILE_NAME T.BYTES/1024/1024/1024||'G'
EFMIS 5 /u01/app/oracle/oradata/orcl/efmis_01.dbf .078125G
EFMIS 6 /u01/app/oracle/oradata/orcl/efmis_02.dbf .078125G
EFMIS 7 /u01/app/oracle/oradata/orcl/efmis_03.dbf .078125G
2、创建测试用户
create user fasp identified by 1 default tablespace efmis;
grant connect,resource to fasp;
3、创建测试表并插入数据
create table fasp.tab1 as select * from dba_objects;
4、查看dba_extents及dba_segments数据相关操作
SQL> select t.tablespace_name,t.segment_name,t.bytes/1024/1024 from dba_segments t where t.owner='FASP';
TABLESPACE_NAME SEGMENT_NAME T.BYTES/1024/1024
EFMIS TAB1 10
SQL> select file_id,sum(bytes)/1024/1024 from dba_extents t where t.owner='FASP' group by file_id;
FILE_ID SUM(BYTES)/1024/1024
6 4
5 3
7 3
SQL> select count(*) from fasp.tab1;
COUNT(*)
86268
SQL> insert into fasp.tab1 select * from fasp.tab1;
86268 rows inserted
SQL> insert into fasp.tab1 select * from fasp.tab1;
172536 rows inserted
SQL> select t.tablespace_name,t.segment_name,t.bytes/1024/1024 from dba_segments t where t.owner='FASP';
TABLESPACE_NAME SEGMENT_NAME T.BYTES/1024/1024
EFMIS TAB1 40
SQL> select file_id,sum(bytes)/1024/1024 from dba_extents t where t.owner='FASP' group by file_id;
FILE_ID SUM(BYTES)/1024/1024
6 14
5 13
7 13
SQL> delete from fasp.tab1;
345072 rows deleted
SQL> commit;
Commit complete
SQL> select count(*) from fasp.tab1;
COUNT(*)
0
SQL> select t.tablespace_name,t.segment_name,t.bytes/1024/1024 from dba_segments t where t.owner='FASP';
TABLESPACE_NAME SEGMENT_NAME T.BYTES/1024/1024
EFMIS TAB1 40
SQL> select file_id,sum(bytes)/1024/1024 from dba_extents t where t.owner='FASP' group by file_id;
FILE_ID SUM(BYTES)/1024/1024
6 14
5 13
7 13
5、结论：
1）tab1表在dba_segments中共1个段，占据10m存储空间。
2）tab1表在dba_extents中分成多个区，总共占10m存储空间。
3）oracle数据库中segment由extent逻辑构成。
4）tab1插入的数据按照hash算法均为分布在所属表空间数据文件下，数据文件创建后不可随意删除，否则将导致部分数据丢失。
5）段相关数据字典：dba_segments,user_segments
区相关数据字典：dba_extents,user_extents
6）dba_segments及dba_extents存储至高水位线空间大小，delete删除数据并不会降低高水位线值。
7）可以通过dba_segments视图查看table及index等数据库对象占用存储空间大小，此时值为起点至高水位线值大小。
6、查看表空间使用率
select a.tablespace_name,
round((a.maxbytes / 1024 / 1024 / 1024), 2) "sum G",
round((a.bytes / 1024 / 1024 / 1024), 2) "datafile G",
round(((a.bytes - b.bytes) / 1024 / 1024 / 1024), 2) "used G",
round(((a.maxbytes - a.bytes + b.bytes) / 1024 / 1024 / 1024), 2) "free G",
round(((a.bytes - b.bytes) / a.maxbytes) * 100, 2) "percent_used(%)"
from (select tablespace_name, sum(sumnow) bytes, sum(summax) maxbytes
from (select t1.tablespace_name,
sum(t1.bytes) sumnow,
sum(t1.maxbytes) summax
from dba_data_files t1
where t1.maxbytes <> 0
group by t1.tablespace_name
union all
select t2.tablespace_name,
sum(t2.bytes) sumnow,
sum(t2.bytes) summax
from dba_data_files t2
where t2.maxbytes = 0
group by t2.tablespace_name)
group by tablespace_name) a,
(select tablespace_name, sum(bytes) bytes
from dba_free_space
group by tablespace_name) b
where a.tablespace_name = b.tablespace_name
order by ((a.bytes - b.bytes) / a.maxbytes) desc;
TABLESPACE_NAME sum G datafile G used G free G percent_used(%)
EFMIS 0.23 0.23 0.04 0.19 17.92
SYSTEM 32 0.82 0.81 31.19 2.52
SYSAUX 32 0.54 0.51 31.49 1.59
UNDOTBS1 32 0.35 0.13 31.87 0.41
USERS 32 0 0 32 0
SQL> select t.tablespace_name,t.file_name,t.file_id,t.bytes/1024/1024,t.autoextensible,t.maxbytes from dba_data_files t where t.tablespace_name='EFMIS';
TABLESPACE_NAME FILE_NAME FILE_ID T.BYTES/1024/1024 AUTOEXTENSIBLE MAXBYTES
EFMIS /u01/app/oracle/oradata/orcl/efmis_01.dbf 5 80 NO 0
EFMIS /u01/app/oracle/oradata/orcl/efmis_02.dbf 6 80 NO 0
EFMIS /u01/app/oracle/oradata/orcl/efmis_03.dbf 7 80 NO 0
7、结论
1）表空间数据文件未设置自动增长，则数据文件最大值（maxbytes）为0，此时数据文件最大值为bytes值大小。
2）表空间由数据文件物理构成。