Partitioning -- 15 : Online Modification of Partitioning Type (Strategy)

Oracle 18c introduces the ability to convert a Partitioned Table from one Type to another -- e.g. from Hash Partitioning to Range Partitioning.  This is effectively a change of the Partitioning strategy for a table without actually having to manually rebuild the table.

I start with a Hash Partitioned Table.

SQL> create table customers(customer_id number, customer_name varchar2(200), customer_city_code number)
  2  partition by hash (customer_id) partitions 4;

Table created.

SQL> select partitioning_type from user_part_tables
  2  where table_name = 'CUSTOMERS'
  3  /

PARTITION
---------
HASH

SQL> select partition_name from user_tab_partitions
  2  where table_name = 'CUSTOMERS'
  3  /

PARTITION_NAME
--------------------------------------------------------------------------------
SYS_P221
SYS_P222
SYS_P223
SYS_P224

SQL>
SQL> insert into  customers
  2  select dbms_random.value(1,1000001), dbms_random.string('X',25), mod(rownum,5)
  3  from dual
  4  connect by level < 1000001
  5  /

1000000 rows created.

SQL> commit;

Commit complete.

SQL> exec dbms_stats.gather_table_stats('','CUSTOMERS');

PL/SQL procedure successfully completed.

SQL> select partition_name, num_rows
  2  from user_tab_partitions
  3  where table_name = 'CUSTOMERS'
  4  /

PARTITION_NAME     NUM_ROWS
---------------- ----------
SYS_P221             250090
SYS_P222             249563
SYS_P223             250018
SYS_P224             250329

SQL>

I now want to convert this Hash Partitioned Table to a Range Partitioned Table online.

SQL> alter table customers
  2  modify
  3  partition by range (customer_id)
  4  (partition P_100K values less than (100001),
  5   partition P_200K values less than (200001),
  6   partition P_300K values less than (300001),
  7   partition P_400K values less than (400001),
  8   partition P_500K values less than (500001),
  9   partition P_600K values less than (600001),
 10   partition P_700K values less than (700001),
 11   partition P_800K values less than (800001),
 12   partition P_900K values less than (900001),
 13   partition P_1MIL values less than (1000001),
 14   partition P_2MIL values less than (2000001),
 15   partition P_MAXVALUE values less than (MAXVALUE))
 16  online;

Table altered.

SQL>
SQL> select partitioning_type
  2  from user_part_tables
  3  where table_name = 'CUSTOMERS'
  4  /

PARTITION
---------
RANGE

SQL> exec dbms_stats.gather_table_stats('','CUSTOMERS');

PL/SQL procedure successfully completed.

SQL> col high_value format a12
SQL> select partition_name, high_value, num_rows
  2  from user_tab_partitions
  3  where table_name = 'CUSTOMERS'
  4  order by partition_position
  5  /

PARTITION_NAME   HIGH_VALUE     NUM_ROWS
---------------- ------------ ----------
P_100K           100001           100116
P_200K           200001            99604
P_300K           300001            99941
P_400K           400001           100048
P_500K           500001            99841
P_600K           600001            99920
P_700K           700001           100081
P_800K           800001           100024
P_900K           900001           100123
P_1MIL           1000001          100302
P_2MIL           2000001               0
P_MAXVALUE       MAXVALUE              0

12 rows selected.

SQL>

The Hash Partitioned Table is now converted to a Range Partitioned Table.  The number of Partitions has been changed.  And the operation was performed online with the ONLINE keyword added to the ALTER TABLE ... statement.  The UPDATE INDEXES clauses can also be used to update existing Indexes on the Table.