Oracle表空间管理

表空间管理是DBA的工作重点之一，所以本节也会用较大的篇幅来阐述数据库表空间相关的重要知识点和注意事项。
区管理和段管理
在日常维护中和表空间管理相关的主要视图如下所示。

视图	描述
V$TABLESPACE	Name and number of all tablespaces from the control file.
DBA_TABLESPACES, USER_TABLESPACES	Descriptions of all (or user accessible) tablespaces.
DBA_TABLESPACE_GROUPS	Displays the tablespace groups and the tablespaces that belong to them.
DBA_SEGMENTS, USER_SEGMENTS	Information about segments within all (or user accessible) tablespaces.
DBA_EXTENTS, USER_EXTENTS	Information about data extents within all (or user accessible) tablespaces.
DBA_FREE_SPACE, USER_FREE_SPACE	Information about free extents within all (or user accessible) tablespaces.
V$DATAFILE	Information about all datafiles, including tablespace number of owning tablespace.
V$TEMPFILE	Information about all tempfiles, including tablespace number of owning tablespace.
DBA_DATA_FILES	Shows files (datafiles) belonging to tablespaces.
DBA_TEMP_FILES	Shows files (tempfiles) belonging to temporary tablespaces.
V$TEMP_EXTENT_MAP	Information for all extents in all locally managed temporary tablespaces.
V$TEMP_EXTENT_POOL	For locally managed temporary tablespaces: the state of temporary space cached and used for by each instance.
V$TEMP_SPACE_HEADER	Shows space used/free for each tempfile.
DBA_USERS	Default and temporary tablespaces for all users.
DBA_TS_QUOTAS	Lists tablespace quotas for all users.
V$SORT_SEGMENT	Information about every sort segment in a given instance. The view is only updated when the tablespace is of the TEMPORARY type.
V$TEMPSEG_USAGE	Describes temporary (sort) segment usage by user for temporary or permanent tablespaces.

最重要的一张视图是DBA_TABLESPACE，其结构如下：

SQL> desc dba_tablespaces
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 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)

这张视图中包含了表空间管理中的几个重要知识点：
1.区（EXTENT）的管理方式
区（EXTENT）管理主要有数据字典管理方式（DMT）和本地管理方式（LMT）两种。在Oracle 8i之前，区管理均采用数据字典管理方式，其原理就是在Oracle基表SYS.FET 和 S Y S .