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Oracle Parallel Query

Oracle Tips by Burleson Consulting

The Data Warehouse Development Life Cycle

Parallelism And Oracle Data Warehousing

Oracle Parallel Query

One of the most exciting performance features of Oracle version 7.3 and above is the ability to partition an SQL query into sub-queries and dedicate separate processors to concurrently service each sub-query. At this time, parallel query is only useful for queries that perform full-table scans on long tables, but the performance improvements can be dramatic.

Parallel queries are most useful in distributed databases where a single logical table has been partitioned into smaller tables at each remote node. For example, a customer table ordered by customer name may be partitioned into a customer table at each remote database, such that we have a PHOENIX_CUSTOMER, a LOS_ANGELES_CUSTOMER, and so on. This approach is very common with distributed databases where local autonomy of processing is important. However, what about the needs of those in corporate headquarters? How can they query all of these remote tables as a single unit and treat the logical customer table as a single entity? For large queries that may span many logical tables, the isolated tables can be easily reassembled using Oracle’s parallel query facility, as follows:

CREATE VIEW all_customer AS
SELECT * FROM PHOENIX_CUSTOMER@phoenix
UNION ALL
SELECT * FROM LOS_ANGELES_CUSTOMER@los_angeles
UNION ALL
SELECT * FROM ROCHESTER_CUSTOMER@rochester;

NOTE: the @ references refer to SQL*Net service names for the remote hosts. For details on distributed Oracle communications, see Chapter 9, Distributed Oracle Data Warehouses.


This is an excerpt from "High Performance Data Warehousing", copyright 1997. 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

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