Oracle Range Partioning

Question:  I have an some sales data that I would like to be able to divide the information by month or quarter in order to be able to do some reporting.  I know that partitioning is an option for this. What is the best type of partitioning for this kind of data?

Answer:  Partitioning is definitely the way to go.  Partitions are smaller divisions of tables, indexes or index-organized tables which can be managed and accessed independently.  Defining an partitioned table involves one or more columns being used as keys to match the row into the appropriate partition.

For your purposes, range partitioning makes the most obvious sense.  Range partitioning has been around in Oracle for a long time.  Data with logical ranges of information lend themselves naturally to range partitions.  Common uses of range partitions include dates, item numbers or serial numbers.

Range partitioning allows an object to be partitioned by a specified range on the partitioning key.  In your case, you can easily create range partitions by month, quarter or year using a column with a defined DATE field.  With the range partion, each month, quarter or year would be stored in the appropriately defined partition.

It is important to note that the range partition for data in the key column must be defined before rows can be matched to that partition.  For example, if you are storing your data in monthly range partitions, you will need to define a new range partition each month before data from that month can be matched and stored in that partition.

An attempt to match new data for which there is no matching range partition would result in the following error:

ORA-14400: inserted partition key does not map to any partition 

Until a new range partition for the key column has been created in the system, the data loading will fail.  If you have a large data warehouse system, this could be a serious problem.  The impacts on reporting, in particular, could be considerable.  To avoid this, most users will create a MAXVALUE partition to catch everything that does not fall into previously existing range partitions.

A range partition using MAXVALUE for data on book sales might look like this:

CREATE TABLE book1 (id NUMBER, c1 DATE)
PARTITION BY RANGE (c1)
 (PARTITION book1p1 VALUES LESS THAN (TO_DATE('2011-01-01', 'YYYY-MM-DD')),
  PARTITION book1p2 VALUES LESS THAN (TO_DATE('2011-02-01', 'YYYY-MM-DD')),
  PARTITION book1p3 VALUES LESS THAN (MAXVALUE) );

 If MAXVALUE is defined as a partition bound for the nth element of the partition list, then any other higher range is irrelevant (and illegal) for values defined in the n+ partition element.

For example, if a partition is defined as:

 partition by range (flda, fldb, fldc, fldd)
    partition pa values less than (v11, v21, v31, v41)
    partition pb values less than (v12, v22, v32, v42)
    partition pc values less than (v13, MAXVALUE, v33, v43)
    partition pd values less than (v14, MAXVALUE, v34, v44)

then, having defined partition pc, partition pd is irrelevant and illegal. Partition pc might as well be:

 partition pc value less than (v13, MAXVALUE, MAXVALUE, MAXVALUE);

Generally, adding range partitions is a manual process.  Arup Nanda has this article on a tool for automatically adding range partitions.

Interval partitioning is an new feature with Oracle 11g and offers an enhancement to range partitioning. 

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