Storage space Management

In the logical structure of a database, table spaces organize different types of data, such as system data, user data, temporary data, rollback data, and so on.
in the same tablespace, the data is organized in a database object , typically one segment for a database object, and a table space with multiple segments.
Stores the data in a database object in a segment, and the storage space occupied by the data is allocated and reclaimed in extents.

A database object occupies a number of extents, so the segment is made up of a number of extents.
When allocating storage space for database objects, one or more extents are allocated at a time.
A zone is the basic unit for allocating and reclaiming storage space, and a zone consists of several contiguous blocks of data.
A data block is the smallest unit of storage in a logical structure and is the basic unit of Oracle's read and write data.

When the user accesses the data, the server process first reads the data from the data block into the database cache and stores it in a buffer that is the same size as the data block, and then reads and writes the data in the buffer.
The data in the database is physically stored on disk and requires a certain operating system block.

A block of data is made up of several operating system blocks, so the size of the data block is an integer multiple of the operating system block.
The database server reads and writes data blocks to read and write to multiple operating system blocks.

Management of segments

In a tablespace, a segment typically represents a database object, and all of the object's data is stored in the corresponding segment.

In general, segments do not need to be created by the user themselves, and segments are automatically generated when database objects are created.
The space allocated for a segment is in a data file in the Tablespace, which consists of several extents.
The relationship between segments, extents, and data blocks.

Type of segment

Oracle 11g supports more than 10 types of segments.

By querying the data dictionary dba_segments, you can get the types of segments that already exist in the current database.

The following is information about the data dictionary dba_segments:

DBA_SEGMENTSDescribes the storage allocated for all segments in the database.

Related View

USER_SEGMENTSDescribes 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.

VARCHAR2 (7)

VARCHAR2 (7)

TD class= "Cellalignment28" headers= "d1066160e609 d1066160e190" > TD class= "Cellalignment28" headers= "d1066160e636 d1066160e190" > TD class= "Cellalignment29" headers= "d1066160e726 d1066160e193" > 

Column	Datatype	NULL	Description
OWNER	VARCHAR2(128)		Username of the segment owner
SEGMENT_NAME	VARCHAR2(128)		Name, if any, of the segment
PARTITION_NAME	VARCHAR2(128)		Object Partition Name (Set to for NULL nonpartitioned objects)
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
SEGMENT_SUBTYPE	VARCHAR2(10)		Subtype of LOB segment: SECUREFILE ,,, ASSM MSSM andNULL
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 being 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
MAX_SIZE	NUMBER		Maximum number of blocks allowed in the segment
RETENTION	VARCHAR2(7)		Retention option for SECUREFILE segment
MINRETENTION	NUMBER		Minimum Retention duration for SECUREFILE 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	 	Buffer pool to being used for segment blocks: DEFAULT Code>keep RECYCLE
Flash_cache	 	Database Smart Flash Cache hint to being used for segment blocks: DEFAULT /p> KEEP NONE Solaris and Oracle Linux func Tionality only.
Cell_flash_cache	VARCHAR2 (7)	 	Cell Flash cache hint to being used for segment blocks: default KEEP NONE see Als O: oracle Exadata Storage Server Software documentation for more information
INMEMORY	VARCHAR2 (8)	 	Indicates whether the In-memory column store (IM Column Store) is enabled ( enabled ) or Disab LED ( DISABLED ) for this segment
inmemory_priority 1	VARCHAR2 (8)	Indicates the priority for In-memory column store (IM Column Store) Population: Low MEDIUM High CRITICAL NONE NULL
Inmemory_distribute 1	VARCHAR2 ()	 	Indicates how the IM column store was distributed in an Oracle Real application Clusters (Ora CLE RAC) Environment: AUTO by ROWID RANGE by PARTITION by subpartition
inmemory_duplicate 1	VARCHAR2 (+)	&NBSP;	Indicates the duplicate setting for the IM column store in an Oracle RAC environment: NO DUPLICATE DUPLICATE DUPLICATE all< /code>
INMEMORY_COMPRESSION1	VARCHAR2(17)		Indicates the compression level for the IM column store: NO MEMCOMPRESS FOR DML FOR QUERY [ LOW | HIGH ] FOR CAPACITY [ LOW | HIGH ] NULL

For example:

Storage space Management