From 0c2629efaa4222b81309a558e66c6f9214ce7333 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 16 Dec 2000 22:44:47 +0000
Subject: [PATCH] Update some obsolete info about GEQO.
---
doc/src/sgml/geqo.sgml | 89 ++++++++++--------------------------------
1 file changed, 21 insertions(+), 68 deletions(-)
diff --git a/doc/src/sgml/geqo.sgml b/doc/src/sgml/geqo.sgml
index 0f12b3db3c3..546a864901b 100644
--- a/doc/src/sgml/geqo.sgml
+++ b/doc/src/sgml/geqo.sgml
@@ -1,5 +1,5 @@
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/geqo.sgml,v 1.13 2000/09/29 20:21:33 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/geqo.sgml,v 1.14 2000/12/16 22:44:47 tgl Exp $
Genetic Optimizer
-->
@@ -49,7 +49,7 @@ Genetic Optimizer
grows exponentially with the number of <command>join</command>s included in it. Further
optimization effort is caused by the support of a variety of
<firstterm>join methods</firstterm>
- (e.g., nested loop, index scan, merge join in <productname>Postgres</productname>) to
+ (e.g., nested loop, hash join, merge join in <productname>Postgres</productname>) to
process individual <command>join</command>s and a diversity of
<firstterm>indices</firstterm> (e.g., r-tree,
b-tree, hash in <productname>Postgres</productname>) as access paths for relations.
@@ -57,8 +57,8 @@ Genetic Optimizer
<para>
The current <productname>Postgres</productname> optimizer
- implementation performs a <firstterm>near-
- exhaustive search</firstterm> over the space of alternative strategies. This query
+ implementation performs a <firstterm>near-exhaustive search</firstterm>
+ over the space of alternative strategies. This query
optimization technique is inadequate to support database application
domains that involve the need for extensive queries, such as artificial
intelligence.
@@ -74,8 +74,8 @@ Genetic Optimizer
</para>
<para>
- Performance difficulties within exploring the space of possible query
- plans arose the demand for a new optimization technique being developed.
+ Performance difficulties in exploring the space of possible query
+ plans created the demand for a new optimization technique being developed.
</para>
<para>
@@ -88,10 +88,11 @@ Genetic Optimizer
<title>Genetic Algorithms (<acronym>GA</acronym>)</title>
<para>
- The <acronym>GA</acronym> is a heuristic optimization method which operates through
+ The <acronym>GA</acronym> is a heuristic optimization method which
+ operates through
determined, randomized search. The set of possible solutions for the
optimization problem is considered as a
- <firstterm>erm>popula</firstterm>erm> of <firstterm>individuals</firstterm>.
+ <firstterm>population</firstterm> of <firstterm>individuals</firstterm>.
The degree of adaption of an individual to its environment is specified
by its <firstterm>fitness</firstterm>.
</para>
@@ -167,7 +168,8 @@ P''(t) generation of descendants at a time t
</programlisting>
is encoded by the integer string '4-1-3-2',
which means, first join relation '4' and '1', then '3', and
- then '2', where 1, 2, 3, 4 are relids in <productname>Postgres</productname>.
+ then '2', where 1, 2, 3, 4 are relids within the
+ <productname>Postgres</productname> optimizer.
</para>
<para>
@@ -192,9 +194,10 @@ P''(t) generation of descendants at a time t
<listitem>
<para>
- Usage of <firstterm>edge recombination crossover</firstterm> which is especially suited
+ Usage of <firstterm>edge recombination crossover</firstterm> which is
+ especially suited
to keep edge losses low for the solution of the
- <acronym>cro</acronym>cronym> by means of a <acronym>GA</acronym>;
+ <acronym>TSP</acronym> by means of a <acronym>GA</acronym>;
</para>
</listitem>
@@ -208,40 +211,19 @@ P''(t) generation of descendants at a time t
</para>
<para>
- The <acronym>GEQO</acronym> module gives the following benefits to
- the <productname>Postgres</productname> DBMS
- compared to the <productname>Postgres</productname> query optimizer implementation:
-
- <itemizedlist spacing="compact" mark="bullet">
- <listitem>
- <para>
- Handling of large <command>join</command> queries through non-exhaustive search;
- </para>
- </listitem>
-
- <listitem>
- <para>
- Improved cost size approximation of query plans since no longer
- plan merging is needed (the <acronym>GEQO</acronym> module evaluates the cost for a
- query plan as an individual).
- </para>
- </listitem>
- </itemizedlist>
+ The <acronym>GEQO</acronym> module allows
+ the <productname>Postgres</productname> query optimizer to
+ support large <command>join</command> queries effectively through
+ non-exhaustive search.
</para>
- </sect1>
-
- <sect1 id="geqo-future">
+ <sect2 id="geqo-future">
<title>Future Implementation Tasks for
<productname>PostgreSQL</> <acronym>GEQO</acronym></title>
- <sect2>
- <title>Basic Improvements</title>
-
- <sect3>
- <title>Improve genetic algorithm parameter settings</title>
-
<para>
+ Work is still needed to improve the genetic algorithm parameter
+ settings.
In file <filename>backend/optimizer/geqo/geqo_params.c</filename>, routines
<function>gimme_pool_size</function> and <function>gimme_number_generations</function>,
we have to find a compromise for the parameter settings
@@ -259,38 +241,9 @@ P''(t) generation of descendants at a time t
</listitem>
</itemizedlist>
</para>
- </sect3>
-
- <sect3>
- <title>Find better solution for integer overflow</title>
-
- <para>
- In file <filename>backend/optimizer/geqo/geqo_eval.c</filename>, routine
- <function>geqo_joinrel_size</function>,
- the present hack for MAXINT overflow is to set the <productname>Postgres</productname> integer
- value of <structfield>rel->size</structfield> to its logarithm.
- Modifications of <structname>Rel</structname> in <filename>backend/nodes/relation.h</filename> will
- surely have severe impacts on the whole <productname>Postgres</productname> implementation.
- </para>
- </sect3>
-
- <sect3>
- <title>Find solution for exhausted memory</title>
- <para>
- Memory exhaustion may occur with more than 10 relations involved in a query.
- In file <filename>backend/optimizer/geqo/geqo_eval.c</filename>, routine
- <function>gimme_tree</function> is recursively called.
- Maybe I forgot something to be freed correctly, but I dunno what.
- Of course the <structname>rel</structname> data structure of the
- <command>join</command> keeps growing and
- growing the more relations are packed into it.
- Suggestions are welcome :-(
- </para>
- </sect3>
</sect2>
-
<bibliography id="geqo-biblio">
<title>
References
--
GitLab