Oracle 11g New Features TipsReference partitioning is a new partitioning option in Oracle 11g that allows the partitioning of two related tables to be based on a referential constraint. In other words, when there is a parent-child relationship between two tables, the parent table can be defined with its partitions. Subsequently, the child table can be equipartitioned by defining the child table to inherit the partitioning key from the parent table, without the need to duplicate the partition key columns. This logical partitioning is achieved by the inheritance of the parents partitioning scheme through a referential constraint in the child table. This feature enhances the manageability of the child table because all partition maintenance operations on the parent table automatically cascade to the child table. Additionally, this relieves the DBA of the responsibility of maintaining duplicate columns, and partitions in the child table, in order to achieve the same objective. Using Reference PartitioningIn a relational database, there are a countless number of situations where parent-child relationships exist. Consider the abundance of parent-child table relationships in Oracle schemas that support online transaction processing or data warehousing. For example, consider the following two tables based on an order management schema.The table order_headers is a parent table that stores the header level information about a sales order. The business has made the decision to partition this table by sales regions North, East, South, and West. The table is created with the following statement:create table
order_headers (
header_id number primary key,
order_date date,
sales_region varchar2(1) not null
)
partition by
list (sales_region)
(
partition pN values ('N'),
partition pE values ('E'),
partition pS values ('S'),
partition pW values ('W')
);The table order_lines is a child table of the order_headers table and has a foreign key constraint fk_lines_0 on header_id with its parent table. The order_lines table is defined as:create table
order_lines (
line_id number primary key,
header_id number not null,
customer_id number,
product_id number,
quantity number,
price number,
constraint fk_lines_0
foreign key (header_id)
references order_headers
);Given the child-parent relationship of order_lines with order_headers, it would be best to partition order_lines by sales_region in order to take full advantage of partition-wise joins and enhances the manageability of these tables. However, this column is not included in the child table. Prior to 11g, this would be accomplished by duplicating the sales_region column in the order_lines table. The DBA would then be forced to define and manage the partitions from both tables independently. However, by using reference partitioning in Oracle 11g, it is easy to equi-partition order_lines with its parent by using the foreign key constraint as such:create table
order_lines (
line_id number primary key,
header_id number not null,
customer_id number,
product_id number,
quantity number,
price number,
constraint fk_lines_0
foreign key (header_id)
references order_headers
)
partition by
reference (fk_lines_0);This table now inherits the partitioning scheme from its parent table by reference without needing to include sales_region in the order_lines table. The partitions for order_lines are created identical to its parent. Order_headers, and any maintenance operations on the partitions of order_headers, will automatically cascade to its child table, order_lines. To view the partitions created for order_lines, use the dictionary views dba_part_tables and dba_tab_partitions:select
table_name,
partition_count,
ref_ptn_constraint_name
from
dba_part_tables
where
table_name = 'ORDER_LINES';

TABLE_NAME PARTITION_COUNT REF_PTN_CONSTRAINT_NAME
------------- ------------------ -----------------------
ORDER_LINES 4 FK_LINES_0select
partition_name
from
dba_tab_partitions
where
table_name = 'ORDER_LINES';PARTITION_NAME
--------------
PE
PS
PW
PNLimitations of reference partitioning cannot be used when the parent table uses interval partitioning. Referential constraint on child table must be defined on a NOT NULL parent column and a virtual column cannot be part of the partitioning foreign key. Violating any of these limitations will cause an error such as: ORA-14652: reference partitioning foreign key is not supportedReference partitioning improves and simplifies the partitioning of tables that have a parent-child relationship. It also allows the DBA to maintain both sets of partitions by only managing partitions on the parent table. This removes the necessity for managing the partitions on the child table. Similarly, reference partitioning also eliminates the need to include unnecessary duplicate columns from the parent table to enable equi-partitioning of the child table.