Partitioning

All the examples shown here use the users tablespace for all partitions

PARTITIONING

All the examples shown here use the users tablespace for all partitions. In a real situation it is likely that these partitions would be assigned to different tablespaces to reduce device contention.

Range Partitioning Tables

Hash Partitioning Tables

Composite Partitioning Tables

List Partitioning (Only with 9i above) Composite Range-List Partitioning (Only with 9i above) Partitioning Indexes

Local Prefixed Indexes

Local Non-Prefixed Indexes

Global Prefixed Indexes

Global Non-Prefixed Indexes

Partitioning Existing Tables

Range Partitioning Tables

Range partitioning is useful when you have distinct ranges of data you want to store together. The classic example of this is the use of dates. Partitioning a table using date ranges allows all data of a similar age to be stored in same partition. Once historical data is no longer needed the whole partition can be removed. If the table is indexed correctly search criteria can limit the search to the partitions that hold data of a correct age:

CREATE TABLE invoices

(invoice_no NUMBER NOT NULL,

invoice_date DATE NOT NULL,

comments VARCHAR2(500))

PARTITION BY RANGE (invoice_date)

(PARTITION invoices_q1 VALUES LESS THAN (TO_DATE('01/04/2001', 'DD/MM/YYYY')) TABLESPACE users,

PARTITION invoices_q2 VALUES LESS THAN (TO_DATE('01/07/2001', 'DD/MM/YYYY')) TABLESPACE users,


PARTITION invoices_q4 VALUES LESS THAN (TO_DATE('01/01/2002', 'DD/MM/YYYY')) TABLESPACE users);

Hash Partitioning Tables

Hash partitioning is useful when there is no obvious range key, or range partitioning will cause uneven distribution of data. The number of partitions must be a power of 2 (2, 4, 8, 16...) and can be specified by the PARTITIONS...STORE IN clause:





PARTITION BY HASH (invoice_no)

PARTITIONS 4

STORE IN (users, users, users, users);

or specified individually:





PARTITION BY HASH (invoice_no)

(PARTITION invoices_q1 TABLESPACE users,

PARTITION invoices_q2 TABLESPACE users,


PARTITION invoices_q4 TABLESPACE users);

Composite Range Hash Partitioning Tables

Composite partitioning allows range partitions to be hash subpartitioned on a different key. The greater number of partitions increases the possiblities for parallelism and reduces the chances of contention. The following example will range partition the table on invoice_date and subpartitioned these on the invoice_no giving a totol of 32 subpartitions:





PARTITION BY RANGE (invoice_date)

SUBPARTITION BY HASH (invoice_no)

SUBPARTITIONS 8

(PARTITION invoices_q1 VALUES LESS THAN (TO_DATE('01/04/2001', 'DD/MM/YYYY')),

PARTITION invoices_q2 VALUES LESS THAN (TO_DATE('01/07/2001', 'DD/MM/YYYY')),

PARTITION invoices_q3 VALUES LESS THAN (TO_DATE('01/09/2001', 'DD/MM/YYYY')),

PARTITION invoices_q4 VALUES LESS THAN (TO_DATE('01/01/2002', 'DD/MM/YYYY'));

List Partitioning (Only with 9i above)Under this type of partitioning the records in a table are partitioned based on the List of values for a table with say communities column as a defining key the partitions can be made based on that say in a table we have communities like Government , Asian , Employees , American, European then a List Partition can be created for individual or a group of communities lets say American-partition will have all the records having the community as American.

Lets take one example. In fact, we will modify the same example.CREATE TABLE SAMPLE_ORDERS(ORDER_NUMBER NUMBER,ORDER_DATE DATE,CUST_NUM NUMBER,TOTAL_PRICE NUMBER,TOTAL_TAX NUMBER,TOTAL_SHIPPING NUMBER,SHIP_TO_ZIP_CODE,SHIP_TO_STATE)PARTITION BY LIST (SHIP_TO_STATE)(PARTITION SHIP_TO_ARIZONA VALUES (AZ) TABLESPACE TS01,PARTITION SHIP_TO_CALIFORNIA VALUES (CA) TABLESPACE TS02,PARTITION SHIP_TO_ILLINOIS VALUES (IL) TABLESPACE TS03,PARTITION SHIP_TO_MASACHUSETTES VALUES (MA) TABLESPACE TS04,PARTITION SHIP_TO_MICHIGAN VALUES (MI) TABLESPACE TS05)ENABLE ROW MOVEMENT;The above example creates List partition based on the SHIP_TO_STATE each partition allocated to different table spacesComposite Range-List Partitioning (Only with 9i above)This is also a combination of Range and List Partitions, basically first the data is divided using the Range partition and then each Range partitioned data is further subdivided into List partitions using List key values. Each sub partitions individually represent logical subset of the data not like composite Range-Hash Partition.

Index organized tables can be partitioned using Range or Hash Partitions

Lets modify the above partition once more.CREATE TABLE SAMPLE_ORDERS(ORDER_NUMBER NUMBER,ORDER_DATE DATE,CUST_NUM NUMBER,CUST_NAME VARCAHR2,TOTAL_PRICE NUMBER,TOTAL_TAX NUMBER,TOTAL_SHIPPING NUMBER,SHIP_TO_ZIP_CODE,SHIP_TO_STATE)TABLESPACE USERSPARTITION BY RANGE (ORDER_DATE)SUBPARTITION BY LIST(SHIP_TO_STATE)SUBPARTITION TEMPLATE(SUBPARTITION SP1 TABLESPACE TS01,SUBPARTITION SP2 TABLESPACE TS02,SUBPARTITION SP3 TABLESPACE TS03,SUBPARTITION SP4 TABLESPACE TS04,SUBPARTITION SP5 TABLESPACE TS05)(PARTITION SO99Q1 VALUES LESS THAN TO_DATE(01-APR-1999, DD-MON-YYYY),PARTITION SO99Q2 VALUES LESS THAN TO_DATE(01-JUL-1999, DD-MON-YYYY),PARTITION SO99Q3 VALUES LESS THAN TO_DATE(01-OCT-1999, DD-MON-YYYY),PARTITION SO99Q4 VALUES LESS THAN TO_DATE(01-JAN-2000, DD-MON-YYYY),PARTITION SO00Q1 VALUES LESS THAN TO_DATE(01-APR-2000, DD-MON-YYYY),PARTITION SO00Q2 VALUES LESS THAN TO_DATE(01-JUL-2000, DD-MON-YYYY),PARTITION SO00Q3 VALUES LESS THAN TO_DATE(01-OCT-2000, DD-MON-YYYY),PARTITION SO00Q4 VALUES LESS THAN TO_DATE(01-JAN-2001, DD-MON-YYYY))ENABLE ROW MOVEMENT;Partitioning Indexes

There are two basic types of partitioned index:

Local - All index entries in a single partition will correspond to a single table partition (equipartitioned). They are created with the LOCAL keyword and support partition independance. Equipartioning allows oracle to be more efficient whilst devising query plans.

Global - Index in a single partition may correspond to multiple table partitions. They are created with the GLOBAL keyword and do not support partition independance. Global indexes can only be range partitioned and may be partitioned in such a fashion that they look equipartitioned, but Oracle will not take advantage of this structure.

Both types of indexes can be subdivided further:

Prefixed - The partition key is the leftmost column(s) of the index. Probing this type of index is less costly. If a query specifies the partition key in the where clause partition pruning is possible, that is, not all partitions will be searched.

Non-Prefixed - Does not support partition pruning, but is effective in accessing data that spans multiple partitions. Often used for indexing a column that is not the tables partition key, when you would like the index to be partitioned on the same key as the underlying table.

Local Prefixed Indexes

Assuming the INVOICES table is range partitioned on INVOICE_DATE, the followning are examples of local prefixed indexes:

CREATE INDEX invoices_idx ON invoices (invoice_date) LOCAL;

CREATE INDEX invoices_idx ON invoices (invoice_date) LOCAL





Oracle will generate the partition names and build the partitions in the default tablespace using the default size unless told otherwise.

Local Non-Prefixed Indexes

Assuming the INVOICES table is range partitioned on INVOICE_DATE, the following example is of a local non-prefixed index. The indexed column does not match the partition key:

CREATE INDEX invoices_idx ON invoices (invoice_no) LOCAL





Global Prefixed Indexes

Assuming the INVOICES table is range partitioned on INVOICE_DATE, the followning examples is of a global prefixed index:

CREATE INDEX invoices_idx ON invoices (invoice_date)

GLOBAL PARTITION BY RANGE (invoice_date)

(PARTITION invoices_q1 VALUES LESS THAN (TO_DATE('01/04/2001', 'DD/MM/YYYY')) TABLESPACE users,



PARTITION invoices_q4 VALUES LESS THAN (MAXVALUE) TABLESPACE users);

Note that the partition range values must be specified. The GLOBAL keyword means that Oracle can not assume the partition key is the same as the underlying table.

Global Non-Prefixed Indexes

Oracle does not support Global Non Prefixed indexes.

Partitioning Existing Tables

The ALTER TABLE ... EXCAHNGE PARTITION ... syntax can be used to partition an existing table, as shown by the following example. First we must create a non-partitioned table to act as our starting point.

CREATE TABLE my_table (

id NUMBER,

description VARCHAR2(50)

);

INSERT INTO my_table (id, description) VALUES (1, 'One');

INSERT INTO my_table (id, description) VALUES (2, 'Two');

INSERT INTO my_table (id, description) VALUES (3, 'Three');

INSERT INTO my_table (id, description) VALUES (4, 'Four');

COMMIT;

Next we create a new partitioned table with a single partition to act as our destination table.

CREATE TABLE my_table_2 (

id NUMBER,

description VARCHAR2(50)

)

PARTITION BY RANGE (id)

(PARTITION my_table_part VALUES LESS THAN (MAXVALUE));

Next we switch the original table segment with the partition segment.

ALTER TABLE my_table_2

EXCHANGE PARTITION my_table_part

WITH TABLE my_table

WITHOUT VALIDATION;

We can now drop the original table and rename the partitioned table.

DROP TABLE my_table;

RENAME my_table_2 TO my_table;

Finally we can split the partitioned table into multiple partitions as required and gather new statistics.

ALTER TABLE my_table SPLIT PARTITION my_table_part AT (3)

INTO (PARTITION my_table_part_1,

PARTITION my_table_part_2);

EXEC DBMS_STATS.gather_table_stats(USER, 'MY_TABLE', cascade => TRUE);

The following query shows that the partitioning process is complete.

COLUMN high_value FORMAT A20

SELECT table_name,

partition_name,

high_value,

num_rows

FROM user_tab_partitions

ORDER BY table_name, partition_name;

TABLE_NAME PARTITION_NAME HIGH_VALUE NUM_ROWS

------------------------------ ------------------------------ -------------------- ----------

MY_TABLE MY_TABLE_PART_1 3 2

MY_TABLE MY_TABLE_PART_2 MAXVALUE 2

2 rows selected.

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Partitioning