Quick Demo on deferred_segment_creation

#Example 1

$ sqlplus dbadmin
Enter password:

SQL> show parameter deferred_segment_creation
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------
deferred_segment_creation            boolean     TRUE

SQL> create tablespace DFS datafile size 10M;
Tablespace created.

SQL> SQL> create table JUNK ( col1 number ) tablespace DFS;
Table created.

SQL> SELECT OWNER,SEGMENT_NAME,BYTES/1024/1024 MB FROM DBA_SEGMENTS WHERE SEGMENT_NAME='JUNK';
no rows selected

SQL> insert into JUNK values (100);
1 row created.

SQL> set linesize 168
SQL> SELECT OWNER,SEGMENT_NAME,BYTES/1024/1024 MB FROM DBA_SEGMENTS WHERE SEGMENT_NAME='JUNK';
OWNER      SEGMENT_NAME       MB
---------- ---------------------
DBADMIN    JUNK            .0625

SQL> drop table JUNK;
Table dropped.

#Example 2.

SQL> alter tablespace DFS read only;
Tablespace altered.

SQL> create table JUNK ( col1 number ) tablespace DFS;

Table created.

SQL> SELECT OWNER,SEGMENT_NAME,BYTES/1024/1024 MB FROM DBA_SEGMENTS WHERE SEGMENT_NAME='JUNK';

no rows selected

SQL> insert  into JUNK values (100);
insert  into JUNK values (100)
             *
ERROR at line 1:
ORA-01647: tablespace 'DFS' is read-only, cannot allocate space in it

SQL> alter tablespace DFS read write;
Tablespace altered.

SQL> insert  into JUNK values (100);
1 row created.

SQL> SELECT OWNER,SEGMENT_NAME,BYTES/1024/1024 MB FROM DBA_SEGMENTS WHERE SEGMENT_NAME='JUNK';
OWNER         SEGMENT_NAME       MB
------------- ---------------------
DBADMIN       JUNK            .0625
                           
SQL> commit;
Commit complete.