Oracle Tips  by Burleson Consulting

The Data Warehouse Development Life Cycle

Oracle Features for the Data Warehouse

Oracle Tables in the Data Warehouse
While the act of allocating Oracle tables is very straightforward there are some specific issues that arise when creating a very large table for an Oracle data warehouse. To understand these issues we will look at the allocation of Oracle tables and how the allocation parameters effect system performance.

Table maintenance
As we may know, extended tables are not a concern for the Oracle data warehouse, provided that the tables do not approach their values for maximum extents. Several benchmark studies have shown that tables which have extended to not impeded performance, and they may actually perform faster than a table in a single extent because the data is spread across the disk device. However, we must always be on the lookout for row chaining, which sometimes accompanies table extension. Row chaining occurs when a row within an Oracle table is updated, and a previously NULL column has data added. This will cause the row to physically expand in size, and if there is not enough room on the data block (as defined by the PCTFREE table creation parameter), then the row will fragment, causing a portion of the row to be stored on another block.

Note: For SQL utilities to detect and correct row chaining, see Chapter 10, Oracle Data Warehouse Utilities.

---

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