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Repair error apparently introduced in the initial coding of GUC: the

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default value for geqo_effort is supposed to be 40, not 1.  The actual
'genetic' component of the GEQO algorithm has been practically disabled
since 7.1 because of this mistake.  Improve documentation while at it.
This commit is contained in:
Tom Lane
2004-01-21 23:33:34 +00:00
parent 4d2e94ef04
commit 672a807028
5 changed files with 55 additions and 38 deletions
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24
doc/src/sgml/runtime.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.230 2004/01/10 23:28:43 neilc Exp $
$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.231 2004/01/21 23:33:34 tgl Exp $
-->
<Chapter Id="runtime">
@ -1404,23 +1404,25 @@ SET ENABLE_SEQSCAN TO OFF;
</varlistentry>
<varlistentry>
<term><varname>geqo_effort</varname> (<type>integer</type>)</term>
<term><varname>geqo_generations</varname> (<type>integer</type>)</term>
<term><varname>geqo_pool_size</varname> (<type>integer</type>)</term>
<term><varname>geqo_generations</varname> (<type>integer</type>)</term>
<term><varname>geqo_effort</varname> (<type>integer</type>)</term>
<term><varname>geqo_selection_bias</varname> (<type>floating point</type>)</term>
<listitem>
<para>
Various tuning parameters for the genetic query optimization
algorithm: The pool size is the number of individuals in one
algorithm. The pool size is the number of individuals in one
population. Valid values are between 128 and 1024. If it is set
to 0 (the default) a pool size of 2^(QS+1), where QS is the
number of <literal>FROM</> items in the query, is taken. The effort is used
to calculate a default for generations. Valid values are between
1 and 80, 40 being the default. Generations specifies the number
of iterations in the algorithm. The number must be a positive
integer. If 0 is specified then <literal>Effort *
Log2(PoolSize)</literal> is used. The run time of the algorithm
is roughly proportional to the sum of pool size and generations.
number of <literal>FROM</> items in the query, is used.
Generations specifies the number of iterations of the algorithm.
The value must be a positive integer. If 0 is specified then
<literal>Effort * Log2(PoolSize)</literal> is used.
The run time of the algorithm is roughly proportional to the sum of
pool size and generations.
<varname>geqo_effort</varname> is only used in computing the default
generations setting, as just described. The default value is 40,
and the allowed range 1 to 100.
The selection bias is the selective pressure within the
population. Values can be from 1.50 to 2.00; the latter is the
default.