Modern DBMS support some kind of partitioning with unique techniques and constructions.
The first way to achieve partitions in the Oracle DBMS was with the use
of views; a partitioned table was defined as a view of many tables with the same
layout connected together in ???union all.??? Partitioning pruning, the ability of the
query optimizer to involve only the few necessary partitions in a query instead of
the all partitions, was achieved via an initialization parameter. Starting with Oracle8
and further releases, partitioning constructions were introduced in SQL as specific
???partitioning clauses.??? Each partition can have its storage attributes like distinct
tables, and there is information stored in the dictionary that permits a unified view
of them. Nowadays, in the Oracle DBMS there are three types of partitions: range,
hash, and list, with the possibility of subpartitioning by hash or list.
Partitioning is a fundamental issue in the DW and ETL design because this technique
permits an easy management of history, loading, and query performance. Each row
in a DW fact table has columns named ???date-of-fact??? or ???loading-date???; when one
wants to maintain data for a certain period of time (one month, one year, etc.), one
must label the rows with a date (date-of-fact) and then, via management operation
on tables at every loading cycle, delete old rows, making space for the new records.
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