The three-level bitmap structure within the segment indicates whether blocks below
the HWM are full (less than pctfree), 0 to 25 percent free, 25 to 50 percent free, 50 to 75 percent
free, 75 to 100 percent free, or unformatted.
Data Dictionary Views and Dynamic
Performance Views
A number of data dictionary and dynamic performance views are critical in understanding how
disk space is being used in your database. The data dictionary views that begin with DBA_ are of
a more static nature, whereas the V$ views, as expected, are of a more dynamic nature and give
you up-to-date statistics on how space is being used in the database.
In the next few sections, I??™ll highlight the space management views and provide some quick
examples; later in this chapter, you??™ll see how these views form the basis of Oracle??™s space
management tools.
DBA_TABLESPACES
The view DBA_TABLESPACES contains one row for each tablespace, whether native or currently
plugged in from another database. It contains default extent parameters for objects created in the
tablespace that don??™t specify initial and next values. The EXTENT_MANAGEMENT column indicates
whether the tablespace is locally managed or dictionary managed. As of Oracle 10g, the column
BIGFILE indicates whether the tablespace is a smallfile or a bigfile tablespace. Bigfile tablespaces
are discussed later in this chapter.
In the following query we retrieve the tablespace type and the extent management type for all
tablespaces within the database:
SQL> select tablespace_name, block_size,
2 contents, extent_management from dba_tablespaces;
172 Oracle Database 11g DBA Handbook
TABLESPACE_NAME BLOCK_SIZE CONTENTS EXTENT_MAN
------------------------------ ---------- --------- ----------
SYSTEM 8192 PERMANENT LOCAL
SYSAUX 8192 PERMANENT LOCAL
UNDOTBS1 8192 UNDO LOCAL
TEMP 8192 TEMPORARY LOCAL
USERS 8192 PERMANENT LOCAL
EXAMPLE 8192 PERMANENT LOCAL
DMARTS 16384 PERMANENT LOCAL
XPORT 8192 PERMANENT LOCAL
USERS2 8192 PERMANENT LOCAL
USERS3 8192 PERMANENT LOCAL
USERS4 8192 PERMANENT LOCAL
11 rows selected.
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