DBA_SEGMENTS 数据字典 块数量和发生变化情况

Oracle® Database Reference
10g Release 2 (10.2)
http://docs.oracle.com/cd/B19306_01/server.102/b14237/statviews_4097.htm

DBA_SEGMENTS

DBA_SEGMENTS

describes the storage allocated for all segments in the database.
Related View

USER_SEGMENTS

describes the storage allocated for the segments owned by the current user's objects. This view does not display the

OWNER

,

HEADER_FILE

,

HEADER_BLOCK

, or

RELATIVE_FNO

columns.

Column	Datatype	NULL	Description
OWNER	VARCHAR2(30)		Username of the segment owner
SEGMENT_NAME	VARCHAR2(81)		Name, if any, of the segment
PARTITION_NAME	VARCHAR2(30)		Object Partition Name (Set to NULL for non-partitioned objects)
SEGMENT_TYPE	VARCHAR2(18)		Type of segment: INDEX PARTITION, TABLE PARTITION, TABLE, CLUSTER, INDEX, ROLLBACK, DEFERRED ROLLBACK, TEMPORARY, CACHE, LOBSEGMENT and LOBINDEX
TABLESPACE_NAME	VARCHAR2(30)		Name of the tablespace containing the segment
HEADER_FILE	NUMBER		ID of the file containing the segment header
HEADER_BLOCK	NUMBER		ID of the block containing the segment header
BYTES	NUMBER		Size, in bytes, of the segment
BLOCKS	NUMBER		Size, in Oracle blocks, of the segment
EXTENTS	NUMBER		Number of extents allocated to the segment
INITIAL_EXTENT	NUMBER		Size in bytes requested for the initial extent of the segment at create time. (Oracle rounds the extent size to multiples of 5 blocks if the requested size is greater than 5 blocks.)
NEXT_EXTENT	NUMBER		Size in bytes of the next extent to be allocated to the segment
MIN_EXTENTS	NUMBER		Minimum number of extents allowed in the segment
MAX_EXTENTS	NUMBER		Maximum number of extents allowed in the segment
PCT_INCREASE	NUMBER		Percent by which to increase the size of the next extent to be allocated
FREELISTS	NUMBER		Number of process freelists allocated to this segment
FREELIST_GROUPS	NUMBER		Number of freelist groups allocated to this segment
RELATIVE_FNO	NUMBER		Relative file number of the segment header
BUFFER_POOL	VARCHAR2(7)		Default buffer pool for the object

我查看下表:

SELECT * from dba_segments where segment_name like 'REP_COMMON_STAT'

OWNER           ZMAS

SEGMENT_NAME    REP_COMMON_STAT

PARTITION_NAME

SEGMENT_TYPE    TABLE

TABLESPACE_NAME ZMAS_DATA

HEADER_FILE     56

HEADER_BLOCK    449579

BYTES           6291456

BLOCKS          768

EXTENTS         21

INITIAL_EXTENT  65536

NEXT_EXTENT

MIN_EXTENTS     1

MAX_EXTENTS     2147483645

PCT_INCREASE

FREELISTS

FREELIST_GROUPS

RELATIVE_FNO    6

BUFFER_POOL     DEFAULT

HEADER_FILE 表示在哪个ID的数据文件里;
HEADER_BLOCK 表示段头块的ID号 可别认为是段的整个块数了;
分析下表

analyze table REP_COMMON_STAT compute statistics;

说明：
为什么要收集统计信息，因为dba_tables 中的blocks 是只有收集统计信息以后才有值，而且对于empty_blocks 参数，还必须使用analyze 分析之后才有值。 如果使用dbms_stats.gather_table_stats收集，只能收集到blocks的值，empty_blocks 收集不到。

BACKED_UP    N

NUM_ROWS    58

BLOCKS      748

EMPTY_BLOCKS  19

***G_SPACE     0

CHAIN_CNT    0

***G_ROW_LEN    71

Dba_Segments .blocks = Dba_Tables.Blocks+Dba_Tables.Empty_Blocks +1（segment header block）
这个多加的1是，是segment header block.
如果查询的结果不是这样，可能是你没有分析表。 不妨分析表之后在查一下看看。
这两张表对blocks 的定义也不一样：
DBA_SEGMENTS.BLOCKS holds the total number of blocks allocated to the table.
USER_TABLES.BLOCKS holds the total number of blocks allocated for data.
删除表里的所有数据

delete rep_common_stat;

两个数据表里的信息不发生变更
trncate table rep_common_stat;
数据段的信息发生变化,数据表信息不发生变化.
BYTES 65536
BLOCKS 8
EXTENTS 1