Oracle Online Redefinition

When a table records fragmented, the select statement takes more I/O.

Its causes a performance issue.

Defragmentation help to increase the performance of the data.

Online Redefinition is one of the Method to Defragment the table.

Step 1. Create a table.

SQL> create table ram_test_tab(
2 id number(5),
3 name varchar2(10) default 'RAM',
4 edate date default sysdate);

Table created.

SQL> desc ram_test_tab;
Name Null? Type
----------------------------------------- -------- ----------------------------
ID NUMBER(5)
NAME VARCHAR2(10)
EDATE DATE

Step. 2. The Table Must have a Primary Key:

SQL> alter table ram_test_tab add constraint pk primary key(id);

Table altered.

SQL> begin
2 for i in 1..99999 loop
3 insert into ram_test_tab (id) values(i);
4 end loop;
5 end;
6 / PL/SQL procedure successfully completed.

SQL> commit;

Commit complete.

Step.3 . Collect The Stats about the table.

SQL> analyze table ram_test_tab compute statistics;

Table analyzed.

SQL> select table_name, round((blocks*8),2) "BLOCK",
2 round((num_rows*avg_row_len/1024),2) "SIZE",
3 to_char(last_analyzed,'hh:mm:ss dd/mm/yy')
4 from user_tables
5 where table_name='RAM_TEST_TAB';

TABLE_NAME BLOCK SIZE TO_CHAR(LAST_ANAL
-------------------- ---------- ---------- -----------------
RAM_TEST_TAB 2960 2050.76 04:10:06 31/10/18

Step. 4. Fragment the data:

SQL> delete from ram_test_tab
2 where id between 200 and 20000; 19801 rows deleted.

SQL> analyze table ram_test_tab compute statistics;

Table analyzed.

After collecting statistics the dictionary table updated with latest records.

SQL>select table_name, round((blocks*8),2) "BLOCK",
2 round((num_rows*avg_row_len/1024),2) "SIZE",
3 to_char(last_analyzed,'hh:mm:ss dd/mm/yy')
4 from user_tables
5 where table_name='RAM_TEST_TAB';

TABLE_NAME BLOCK SIZE TO_CHAR(LAST_ANAL
-------------------- ---------- ---------- -----------------
RAM_TEST_TAB 2960 1644.69 04:10:07 31/10/18

Step. 5. Create a Duplicate Table:

If its confirmed fragmentation lead to performance issue. then defragmentation is recommended. Before going to online redefinition package. Create a Dummy table which have same metadata of the fragmented table.

SQL> create table ram_dummy
2 as select * from ram_test_tab
3 where 1=2; Table created.

SQL> desc ram_dummy;
Name Null? Type
----------------------------------------- -------- ----------------------------
ID NUMBER(5)
NAME VARCHAR2(10)
EDATE DATE

SQL> select * from ram_dummy;

no rows selected

Step. 6. Online redefinition package Run:

SQL> conn sys as sysdba
Enter password:
Connected.

SQL> exec dbms_redefinition.can_redef_table('SAKTHI','RAM_TEST_TAB');