diff --git a/doc/src/sgml/geqo.sgml b/doc/src/sgml/geqo.sgml
index 35bb36f22a..a723f4411a 100644
--- a/doc/src/sgml/geqo.sgml
+++ b/doc/src/sgml/geqo.sgml
@@ -1,5 +1,5 @@
@@ -46,8 +46,8 @@ Genetic Optimizer
Among all relational operators the most difficult one to process
and optimize is the join. The number of
- alternative plans to answer a query grows exponentially with the
- number of joins included in it. Further optimization effort is
+ possible query plans grows exponentially with the
+ number of joins in the query. Further optimization effort is
caused by the support of a variety of join
methods (e.g., nested loop, hash join, merge join in
PostgreSQL) to process individual joins
@@ -57,34 +57,30 @@ Genetic Optimizer
- The current PostgreSQL optimizer
- implementation performs a near-exhaustive
- search over the space of alternative strategies. This
- algorithm, first introduced in the System R
- database, produces a near-optimal join order, but can take an
- enormous amount of time and memory space when the number of joins
- in the query grows large. This makes the ordinary
+ The normal PostgreSQL query optimizer
+ performs a near-exhaustive search over the
+ space of alternative strategies. This algorithm, first introduced
+ in IBM's System R database, produces a near-optimal join order,
+ but can take an enormous amount of time and memory space when the
+ number of joins in the query grows large. This makes the ordinary
PostgreSQL query optimizer
inappropriate for queries that join a large number of tables.
The Institute of Automatic Control at the University of Mining and
- Technology, in Freiberg, Germany, encountered the described problems as its
- folks wanted to take the PostgreSQL DBMS as the backend for a decision
- support knowledge based system for the maintenance of an electrical
- power grid. The DBMS needed to handle large join queries for the
- inference machine of the knowledge based system.
-
-
-
- Performance difficulties in exploring the space of possible query
- plans created the demand for a new optimization technique to be developed.
+ Technology, in Freiberg, Germany, encountered some problems when
+ it wanted to use PostgreSQL as the
+ backend for a decision support knowledge based system for the
+ maintenance of an electrical power grid. The DBMS needed to handle
+ large join queries for the inference machine of the knowledge
+ based system. The number of joins in these queries made using the
+ normal query optimizer infeasible.
In the following we describe the implementation of a
- Genetic Algorithm to solve the join
+ genetic algorithm to solve the join
ordering problem in a manner that is efficient for queries
involving large numbers of joins.