怎么理解数据库中dba_segments

Column

Datatype

NULL

Description

OWNER

VARCHAR2(30)

Username of the segment owner

段的拥有者

SEGMENT_NAME

VARCHAR2(81)

Name, if any, of the segment

段的名称

PARTITION_NAME

VARCHAR2(30)

Object Partition Name (Set to NULL for non-partitioned objects)

分区表对应段的名称

SEGMENT_TYPE

VARCHAR2(18)

Type of segment:

* NESTED TABLE

* TABLE

* TABLE PARTITION

* CLUSTER

* LOBINDEX

* INDEX

* INDEX PARTITION

* LOBSEGMENT

* TABLE SUBPARTITION

* INDEX SUBPARTITION

* LOB PARTITION

* LOB SUBPARTITION

* ROLLBACK

* TYPE2 UNDO

* DEFERRED ROLLBACK

* TEMPORARY

* CACHE

* SPACE HEADER

* UNDEFINED

段的类型

SEGMENT_SUBTYPE

VARCHAR2(10)

Subtype of LOB segment: SECUREFILE, ASSM, MSSM, and NULL

LOB段的子类型:SECUREFILE、ASSM、MSSM和NULL

TABLESPACE_NAME

VARCHAR2(30)

Name of the tablespace containing the segment

包含段的表空间的名字

HEADER_FILE

NUMBER

ID of the file containing the segment header

表示这个段的头在哪个数据文件里，因为段可以跨数据文件。

HEADER_BLOCK

NUMBER

ID of the block containing the segment header

表示这个段的头在数据文件的第几个 block里

BYTES

NUMBER

Size, in bytes, of the segment

段的大小，默认：bytes

BLOCKS

NUMBER

Size, in Oracle blocks, of the segment

段占了多少个块

EXTENTS

NUMBER

Number of extents allocated to the segment

分配了多少个 extent

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.)

在创建时为段的初始区段请求的大小(以字节为单位)。(如果请求的大小大于5个块，Oracle将区段大小舍入为5个块的倍数。)

NEXT_EXTENT

NUMBER

Size in bytes of the next extent to be allocated to the segment

下一个分配的 extent 大小（以 byte 计）。如果为空表示是自动分配

MIN_EXTENTS

NUMBER

Minimum number of extents allowed in the segment

最少分配多少个 extent（以个数计）

MAX_EXTENTS

NUMBER

Maximum number of extents allowed in the segment

最多分配多少个 extent（以个数计）

MAX_SIZE

NUMBER

Maximum number of blocks allowed in the segment

最多分配多少个 blocks 大小

RETENTION

VARCHAR2(7)

Retention option for SECUREFILE segment

安全段的保留选项

MINRETENTION

NUMBER

Minimum retention duration for SECUREFILE segment

对于 securefile 段最小保持时间

PCT_INCREASE

NUMBER

Percent by which to increase the size of the next extent to be allocated

下一次 extent 分配增长的百分比

FREELISTS

NUMBER

Number of process freelists allocated to this segment

指定了所有可用于 insert 操作的数据块的列表，管理 HWM 以下的空闲空间

FREELIST_GROUPS

NUMBER

Number of freelist groups allocated to this segment

为此段分配的空闲列表组数

RELATIVE_FNO

NUMBER

Relative file number of the segment header

段头的相对文件号

BUFFER_POOL

VARCHAR2(7)

Buffer pool to be used for segment blocks:

• DEFAULT

• KEEP

• RECYCLE

Buffer pool 中段所使用的 blocks

FLASH_CACHE

VARCHAR2(7)

Database Smart Flash Cache hint to be used for segment blocks:

• DEFAULT

• KEEP

• NONE

Solaris and Oracle Linux functionality only.

数据库 Smart Flash Cache 提示段 blocks方式

CELL_FLASH_CACHE

VARCHAR2(7)

Cell flash cache hint to be used for segment blocks:

• DEFAULT

• KEEP

• NONE

See Also: Oracle Exadata Storage Server Software documentation for more information

Cell flash cache 提示用于表块