可以通过如下的视图，对数据库的空间有一个了解。

1,DBA_USERS视图

SQL> desc dba_users;

 名称                                      是否为空? 类型

 ----------------------------------------- -------- ----------------------------

 USERNAME                                  NOT NULL VARCHAR2(30)

 USER_ID                                   NOT NULL NUMBER

 PASSWORD                                           VARCHAR2(30)

 ACCOUNT_STATUS                            NOT NULL VARCHAR2(32)

 LOCK_DATE                                          DATE

 EXPIRY_DATE                                        DATE

 DEFAULT_TABLESPACE                        NOT NULL VARCHAR2(30)

 TEMPORARY_TABLESPACE                      NOT NULL VARCHAR2(30)

 CREATED                                   NOT NULL DATE

 PROFILE                                   NOT NULL VARCHAR2(30)

 INITIAL_RSRC_CONSUMER_GROUP                        VARCHAR2(30)

 EXTERNAL_NAME                                      VARCHAR2(4000)

通过dba_users视图，可以看到特定的用户的默认表空间，和默认临时表空间在什么地方。

2，DBA_TABLESPACES视图

通过这个视图，可以观察到很多有用的信息。可以看到空间的分配方式，管理方式。块的大小等等。

SQL> desc DBA_TABLESPACES;

 名称                                      是否为空? 类型

 ----------------------------------------- -------- -------------

 TABLESPACE_NAME                           NOT NULL VARCHAR2(30)

 BLOCK_SIZE                                NOT NULL NUMBER

 INITIAL_EXTENT                                     NUMBER

 NEXT_EXTENT                                        NUMBER

 MIN_EXTENTS                               NOT NULL NUMBER

 MAX_EXTENTS                                        NUMBER

 PCT_INCREASE                                       NUMBER

 MIN_EXTLEN                                         NUMBER

 STATUS                                             VARCHAR2(9)

 CONTENTS                                           VARCHAR2(9)

 LOGGING                                            VARCHAR2(9)

 FORCE_LOGGING                                      VARCHAR2(3)

 EXTENT_MANAGEMENT                                  VARCHAR2(10)

 ALLOCATION_TYPE                                    VARCHAR2(9)

 PLUGGED_IN                                         VARCHAR2(3)

 SEGMENT_SPACE_MANAGEMENT                           VARCHAR2(6)

 DEF_TAB_COMPRESSION                                VARCHAR2(8)

 RETENTION                                          VARCHAR2(11)

 BIGFILE                                            VARCHAR2(3)

3，DBA_DATA_FILES视图

SQL> desc DBA_DATA_FILES

 名称                                      是否为空? 类型

 ----------------------------------------- -------- --------------

 FILE_NAME                                          VARCHAR2(513)

 FILE_ID                                            NUMBER

 TABLESPACE_NAME                                    VARCHAR2(30)

 BYTES                                              NUMBER

 BLOCKS                                             NUMBER

 STATUS                                             VARCHAR2(9)

 RELATIVE_FNO                                       NUMBER

 AUTOEXTENSIBLE                                     VARCHAR2(3)

 MAXBYTES                                           NUMBER

 MAXBLOCKS                                          NUMBER

 INCREMENT_BY                                       NUMBER

 USER_BYTES                                         NUMBER

 USER_BLOCKS                                        NUMBER

 ONLINE_STATUS                                      VARCHAR2(7)

从file_name可以看到文件的存储位置，关联的表空间，数据文件的扩展方式。Bytes为当前数据文件分配的空间大小，AUTOEXTENSIBLE标识数据文件是否扩展，INCREMENT_BY为增长的大小，单位为多少个数据块。

4.DBA_free_space

SQL> desc DBA_free_space

 名称                                      是否为空? 类型

 ----------------------------------------- -------- -------

 TABLESPACE_NAME                                    VARCHAR

 FILE_ID                                            NUMBER

 BLOCK_ID                                           NUMBER

 BYTES                                              NUMBER

 BLOCKS                                             NUMBER

 RELATIVE_FNO                                       NUMBER

5 all_segments

SQL> desc dba_segments;

 名称                                      是否为空? 类型

 ----------------------------------------- -------- --------------

 OWNER                                              VARCHAR2(30)

 SEGMENT_NAME                                       VARCHAR2(81)

 PARTITION_NAME                                     VARCHAR2(30)

 SEGMENT_TYPE                                       VARCHAR2(18)

 TABLESPACE_NAME                                    VARCHAR2(30)

 HEADER_FILE                                        NUMBER

 HEADER_BLOCK                                       NUMBER

 BYTES                                              NUMBER

 BLOCKS                                             NUMBER

 EXTENTS                                            NUMBER

 INITIAL_EXTENT                                     NUMBER

 NEXT_EXTENT                                        NUMBER

 MIN_EXTENTS                                        NUMBER

 MAX_EXTENTS                                        NUMBER

 PCT_INCREASE                                       NUMBER

 FREELISTS                                          NUMBER

 FREELIST_GROUPS                                    NUMBER

 RELATIVE_FNO                                       NUMBER

 BUFFER_POOL                                        VARCHAR2(7)

6.user_tables/dba_tables

Row_nums,blocks,empty_blocks

7,user_indexes/dba_indexes

其中user_tables、dba_indexes等表中的数据，那些关键有用的信息，必须进行统计信息的收集，才可以看到。