怎么理解數據庫中dba_segments

Column

Datatype

NULL

Description

OWNER

VARCHAR2(30)

Username of the segment owner

段的擁有者

SEGMENT_NAME

VARCHAR2(81)

Name, if any, of the segment

段的名稱

PARTITION_NAME

VARCHAR2(30)

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

分區(qū)表對應段的名稱

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

段的類型

SEGMENT_SUBTYPE

VARCHAR2(10)

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

LOB段的子類型:SECUREFILE、ASSM、MSSM和NULL

TABLESPACE_NAME

VARCHAR2(30)

Name of the tablespace containing the segment

包含段的表空間的名字

HEADER_FILE

NUMBER

ID of the file containing the segment header

表示這個段的頭在哪個數據文件里，因為段可以跨數據文件。

HEADER_BLOCK

NUMBER

ID of the block containing the segment header

表示這個段的頭在數據文件的第幾個 block里

BYTES

NUMBER

Size, in bytes, of the segment

段的大小，默認：bytes

BLOCKS

NUMBER

Size, in Oracle blocks, of the segment

段占了多少個塊

EXTENTS

NUMBER

Number of extents allocated to the segment

分配了多少個 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.)

在創(chuàng)建時為段的初始區(qū)段請求的大小(以字節(jié)為單位)。(如果請求的大小大于5個塊，Oracle將區(qū)段大小舍入為5個塊的倍數。)

NEXT_EXTENT

NUMBER

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

下一個分配的 extent 大?。ㄒ?byte 計）。如果為空表示是自動分配

MIN_EXTENTS

NUMBER

Minimum number of extents allowed in the segment

最少分配多少個 extent（以個數計）

MAX_EXTENTS

NUMBER

Maximum number of extents allowed in the segment

最多分配多少個 extent（以個數計）

MAX_SIZE

NUMBER

Maximum number of blocks allowed in the segment

最多分配多少個 blocks 大小

RETENTION

VARCHAR2(7)

Retention option for SECUREFILE segment

安全段的保留選項

MINRETENTION

NUMBER

Minimum retention duration for SECUREFILE segment

對于 securefile 段最小保持時間

PCT_INCREASE

NUMBER

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

下一次 extent 分配增長的百分比

FREELISTS

NUMBER

Number of process freelists allocated to this segment

指定了所有可用于 insert 操作的數據塊的列表，管理 HWM 以下的空閑空間

FREELIST_GROUPS

NUMBER

Number of freelist groups allocated to this segment

為此段分配的空閑列表組數

RELATIVE_FNO

NUMBER

Relative file number of the segment header

段頭的相對文件號

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.

數據庫 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 提示用于表塊