Oracle Tips  by Burleson Consulting

The Data Warehouse Development Life Cycle

Oracle Features for the Data Warehouse
Oracle Tablespace Considerations

Choosing how to place tables and indexes into tablespaces has a great impact on the performance of your data warehouse. Since the designer has many choices, it is a good idea to explore the available options. In general, the following characteristics apply for data warehousing:

* Group tables with similar characteristics in a tablespace. For example, all tables that are read-only could be grouped into a single, read-only tablespace. Tables with random I/O patterns could also be grouped together; all small tables should be grouped together, and so on.

* Create at least two tablespaces for use by the TEMP tablespaces. This approach has the advantage of allowing the designer to dedicate numerous TEMP tablespaces to specific classes of users. As we know, the TEMP tablespace is used for large sorting operations, and assigning appropriately sized TEMP tablespaces to users depending upon their sorting requirements can enhance performance. Remember, in a distributed SQL query, the rows are fetched from the remote database and sorted on the Oracle that initiated the request. The use of multiple TEMP tablespaces has the added advantage of allowing the developer to switch TEMP tablespaces in case of disk failure.

* Use many small, manageable tablespaces. This approach makes it easier to take a single tablespace offline for maintenance without affecting the entire system. Oracle highly recommends that no tablespace should ever become greater the 10 GB, and placing all tables into a single tablespace also reduces recoverability in case of media failure. However, this approach does not advocate creating a single tablespace for each table in a system. For example, Oracle recommends that the system tablespace contain only systems tables, and that a separate tablespace be created for the exclusive use of the rollback segments.

* Place the rollback segments in a separate tablespace. This isolates the activity of the rollback segments (which tend to have a high I/O rate) from the data files belonging to the application.

* If you have Oracle8, Partition large table and indexes into separate tablespaces. For a discussion of this method, see Chapter 14, Oracle8 for the Warehouse.

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This is an excerpt from "High Performance Data Warehousing". To learn more about Oracle, try "Oracle Tuning: The Definitive Reference", by Donald K. Burleson.  You can buy it direct from the publisher at 30% off here:
http://www.rampant-books.com/book_1002_oracle_tuning_definitive_reference_2nd_ed.htm