ORACLE 10gR2 估算表所需的空间

1、估算表容量
1）创建测试表和表空间

SQL> create table t as select * from dba_objects;
 
Table created
 
SQL> create index t_ind on t(object_id);
 
Index created

2）收集统计信息

 
SQL> exec dbms_stats.gather_table_stats(user,'T',cascade => true);
 
PL/SQL procedure successfully completed

3）计算表的平均长度

SQL> select count(*) from t;
 
  COUNT(*)
----------
     50805
 
SQL> select a.segment_name,a.segment_type,a.BYTES from user_segments a where a.segment_name in ('T','T_IND');
 
SEGMENT_NAME    SEGMENT_TYPE          BYTES
------------- ------------------ ----------
T              TABLE                 6291456
T_IND          INDEX                 983040

--让我们来顺便计算一下该表中的索引和表大小的百分比

SQL> select trunc((983040/6291456)*100) as "ind_pct(%)" from dual;
 
ind_pct(%)
----------
        15

现在我们可以估算这张表数据的大小了。

比如说我们最终估计这个表保存的数据大概在10亿条，我们就可以算出这张表所需空间大小。

SQL> select ((6291456+983040)/50805*1000000000)/1024/1024/1024 as "T表所需空间大小(G)" from dual;
 
       T表所需空间大小(G)
------------------
  133.351094257455

2、正式环境

真实环境下面有product这张表，最终估计商品总数应该不会超过100w条。

1）收集统计信息

SQL> exec dbms_stats.gather_table_stats(user,tabname => 'PRODUCT',cascade => true);
 
PL/SQL procedure successfully completed

2）我们先找出这张表上面所有的索引

SQL> select index_name,index_type,table_name from user_indexes where table_name ='PRODUCT';
 
INDEX_NAME                     INDEX_TYPE                  TABLE_NAME
------------------------------ --------------------------- ------------------------------
PRODUCT_ID                     NORMAL                      PRODUCT
SYS_IL0000054761C00013$       LOB                         PRODUCT
VISICOUNT2                     NORMAL                      PRODUCT
PRODUCT_STATUS                 NORMAL                      PRODUCT
SID_INDEX2                     NORMAL                      PRODUCT
PRODUCT_NAME2                  NORMAL                      PRODUCT
CREATE_TIME2                   NORMAL                      PRODUCT
CREATE_SID2                    NORMAL                      PRODUCT
SYS_IL0000054761C00118$       LOB                         PRODUCT
 
9 rows selected

3)查看该表和索引空间的大小

select a.segment_name, a.segment_type, a.BYTES
  from user_segments a
 where a.segment_name in
       (select INDEX_NAME from user_indexes where table_name = 'PRODUCT')
    or a.segment_name = 'PRODUCT';
 
SEGMENT_NAME                                                                     SEGMENT_TYPE            BYTES
-------------------------------------------------------------------------------- ------------------ ----------
PRODUCT                                                                          TABLE                 5242880
SYS_IL0000054761C00013$                                                         LOBINDEX                65536
PRODUCT_ID                                                                       INDEX                  196608
CREATE_SID2                                                                      INDEX                  458752
CREATE_TIME2                                                                     INDEX                  327680
PRODUCT_NAME2                                                                    INDEX                  524288
SID_INDEX2                                                                       INDEX                  196608
PRODUCT_STATUS                                                                   INDEX                  196608
VISICOUNT2                                                                       INDEX                  131072
SYS_IL0000054761C00118$                                                         LOBINDEX                65536
 
10 rows selected

4）统计大小

select sum(a.BYTES)
  from user_segments a
 where a.segment_name in
       (select INDEX_NAME from user_indexes where table_name = 'PRODUCT')
    or a.segment_name = 'PRODUCT';
 
SUM(A.BYTES)
------------
     7405568

5）查询表的总大小

SQL> select count(*) from product;
 
  COUNT(*)
----------
      2572

假如有100w条数据算出大小

SQL> select ((7405568/2572)*1000000)/1024/1024/1024  as "PRODUCT表所需空间(G)" from dual;
 
     PRODUCT表所需空间(G)
--------------------
    2.68156013073484