Displaying Information About Space Usage for Schema Objects

Oracle Database provides data dictionary views and PL/SQL packages that allow you to display information about the space usage of schema objects. Views and packages that are unique to a particular schema object are described in the chapter of this book associated with that object. This section describes views and packages that are generic in nature and apply to multiple schema objects.

Using PL/SQL Packages to Display Information About Schema Object Space Usage

These DBMS_SPACE subprograms provide information about schema objects:

Package and Procedure/Function	Description
`DBMS_SPACE.UNUSED_SPACE`	Returns information about unused space in an object (table, index, or cluster).
`DBMS_SPACE.FREE_BLOCKS`	Returns information about free data blocks in an object (table, index, or cluster) whose segment free space is managed by free lists (segment space management is `MANUAL`).
`DBMS_SPACE.SPACE_USAGE`	Returns information about free data blocks in an object (table, index, or cluster) whose segment space management is `AUTO`.

Schema Objects Space Usage Data Dictionary Views

These views display information about space usage in schema objects:

View	Description
`DBA_SEGMENTS` `USER_SEGMENTS`	DBA view describes storage allocated for all database segments. User view describes storage allocated for segments for the current user.
`DBA_EXTENTS` `USER_EXTENTS`	DBA view describes extents comprising all segments in the database. User view describes extents comprising segments for the current user.
`DBA_FREE_SPACE` `USER_FREE_SPACE`	DBA view lists free extents in all tablespaces. User view shows free space information for tablespaces for which the user has quota.

The following sections contain examples of using some of these views.

Example 1: Displaying Segment Information

The following query returns the name and size of each index segment in schema hr:

SELECT SEGMENT_NAME, TABLESPACE_NAME, BYTES, BLOCKS, EXTENTS
    FROM DBA_SEGMENTS
    WHERE SEGMENT_TYPE = 'INDEX'
    AND OWNER='HR'
    ORDER BY SEGMENT_NAME;

The query output is:

SEGMENT_NAME              TABLESPACE_NAME    BYTES BLOCKS EXTENTS
------------------------- --------------- -------- ------ -------
COUNTRY_C_ID_PK           EXAMPLE            65536     32       1
DEPT_ID_PK                EXAMPLE            65536     32       1
DEPT_LOCATION_IX          EXAMPLE            65536     32       1
EMP_DEPARTMENT_IX         EXAMPLE            65536     32       1
EMP_EMAIL_UK              EXAMPLE            65536     32       1
EMP_EMP_ID_PK             EXAMPLE            65536     32       1
EMP_JOB_IX                EXAMPLE            65536     32       1
EMP_MANAGER_IX            EXAMPLE            65536     32       1
EMP_NAME_IX               EXAMPLE            65536     32       1
JHIST_DEPARTMENT_IX       EXAMPLE            65536     32       1
JHIST_EMPLOYEE_IX         EXAMPLE            65536     32       1
JHIST_EMP_ID_ST_DATE_PK   EXAMPLE            65536     32       1
JHIST_JOB_IX              EXAMPLE            65536     32       1
JOB_ID_PK                 EXAMPLE            65536     32       1
LOC_CITY_IX               EXAMPLE            65536     32       1
LOC_COUNTRY_IX            EXAMPLE            65536     32       1
LOC_ID_PK                 EXAMPLE            65536     32       1
LOC_STATE_PROVINCE_IX     EXAMPLE            65536     32       1
REG_ID_PK                 EXAMPLE            65536     32       1

19 rows selected.

Example 2: Displaying Extent Information

Information about the currently allocated extents in a database is stored in the DBA_EXTENTS data dictionary view. For example, the following query identifies the extents allocated to each index segment in the hr schema and the size of each of those extents:

SELECT SEGMENT_NAME, SEGMENT_TYPE, TABLESPACE_NAME, EXTENT_ID, BYTES, BLOCKS
    FROM DBA_EXTENTS
    WHERE SEGMENT_TYPE = 'INDEX'
    AND OWNER='HR'
    ORDER BY SEGMENT_NAME;

The query output is:

SEGMENT_NAME              SEGMENT_TYPE TABLESPACE_NAME EXTENT_ID    BYTES BLOCKS
------------------------- ------------ --------------- --------- -------- ------
COUNTRY_C_ID_PK           INDEX        EXAMPLE                 0    65536     32
DEPT_ID_PK                INDEX        EXAMPLE                 0    65536     32
DEPT_LOCATION_IX          INDEX        EXAMPLE                 0    65536     32
EMP_DEPARTMENT_IX         INDEX        EXAMPLE                 0    65536     32
EMP_EMAIL_UK              INDEX        EXAMPLE                 0    65536     32
EMP_EMP_ID_PK             INDEX        EXAMPLE                 0    65536     32
EMP_JOB_IX                INDEX        EXAMPLE                 0    65536     32
EMP_MANAGER_IX            INDEX        EXAMPLE                 0    65536     32
EMP_NAME_IX               INDEX        EXAMPLE                 0    65536     32
JHIST_DEPARTMENT_IX       INDEX        EXAMPLE                 0    65536     32
JHIST_EMPLOYEE_IX         INDEX        EXAMPLE                 0    65536     32
JHIST_EMP_ID_ST_DATE_PK   INDEX        EXAMPLE                 0    65536     32
JHIST_JOB_IX              INDEX        EXAMPLE                 0    65536     32
JOB_ID_PK                 INDEX        EXAMPLE                 0    65536     32
LOC_CITY_IX               INDEX        EXAMPLE                 0    65536     32
LOC_COUNTRY_IX            INDEX        EXAMPLE                 0    65536     32
LOC_ID_PK                 INDEX        EXAMPLE                 0    65536     32
LOC_STATE_PROVINCE_IX     INDEX        EXAMPLE                 0    65536     32
REG_ID_PK                 INDEX        EXAMPLE                 0    65536     32

19 rows selected.

For the hr schema, no segment has multiple extents allocated to it.

Example 3: Displaying the Free Space (Extents) in a Tablespace

Information about the free extents (extents not allocated to any segment) in a database is stored in the DBA_FREE_SPACE data dictionary view. For example, the following query reveals the amount of free space available as free extents in the SMUNDO tablespace:

SELECT TABLESPACE_NAME, FILE_ID, BYTES, BLOCKS
    FROM DBA_FREE_SPACE
    WHERE TABLESPACE_NAME='SMUNDO';

The query output is:

TABLESPACE_NAME  FILE_ID    BYTES BLOCKS
--------------- -------- -------- ------
SMUNDO                 3    65536     32
SMUNDO                 3    65536     32
SMUNDO                 3    65536     32
SMUNDO                 3    65536     32
SMUNDO                 3    65536     32
SMUNDO                 3    65536     32
SMUNDO                 3   131072     64
SMUNDO                 3   131072     64
SMUNDO                 3    65536     32
SMUNDO                 3  3407872   1664

10 rows selected.