For example, sales by region of the country may create a partition for NY, CT, MA, and VT,
and another partition for IL, WI, IA, and MN. Any sales from elsewhere in the world may be
assigned to its own partition when the state code is missing.
Hash Partitions A hash partition assigns a row to a partition based on a hashing function,
specifying the column or columns used in the hashing function, but not explicitly assigning
the partition, only specifying how many partitions are available. Oracle will assign the row
to a partition and ensure a balanced distribution of rows in each partition.
Hash partitions are useful when there is no clear list or range-partitioning scheme given
the types of columns in the table, or when the relative sizes of the partitions change frequently,
requiring repeated manual adjustments to the partitioning scheme.
Composite Partitions Even further refinement of the partitioning process is available with
composite partitions. For example, a table may be partitioned by range, and within each range,
subpartitioned by list or by hash. New combinations in Oracle 11g include list-hash, list-list, listrange,
and range-range partitioning.
Partitioned Indexes
You can also partition indexes on a table, either matching the partition scheme of the table being
indexed (local indexes) or partitioned independently from the partition scheme of the table (global
indexes). Local partitioned indexes have the advantage of increased availability of the index when
partition operations occur; for example, archiving and dropping the partition FY2002Q4 and its
local index will not affect index availability for the other partitions in the table.
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