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Clarify meaning of GEQO_THRESHOLD parameter.

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Tom Lane 2001-02-15 04:28:50 +00:00
parent 52cacf46b4
commit 21deb42897
1 changed files with 6 additions and 5 deletions
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doc/src/sgml/runtime.sgml
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@ -1,5 +1,5 @@
<!-- <!--
$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.50 2001/02/10 00:50:18 petere Exp $ $Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.51 2001/02/15 04:28:50 tgl Exp $
--> -->
<Chapter Id="runtime"> <Chapter Id="runtime">
@ -639,7 +639,7 @@ env PGOPTIONS='-c geqo=off' psql
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 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 set to 0 (the default) a pool size of 2^(QS+1), where QS
is the number of relations in the query, is taken. The effort is the number of FROM items in the query, is taken. The effort
is used to calculate a default for generations. Valid values is used to calculate a default for generations. Valid values
are between 1 and 80, 40 being the default. Generations are between 1 and 80, 40 being the default. Generations
specifies the number of iterations in the algorithm. The specifies the number of iterations in the algorithm. The
@ -659,9 +659,10 @@ env PGOPTIONS='-c geqo=off' psql
<term>GEQO_THRESHOLD (<type>integer</type>)</term> <term>GEQO_THRESHOLD (<type>integer</type>)</term>
<listitem> <listitem>
<para> <para>
Only use genetic query optimization for queries with at least Use genetic query optimization to plan queries with at least
this many relations involved. The default is 11. For less this many FROM items involved. (Note that a JOIN construct
relations it is probably more efficient to use the counts as only one FROM item.) The default is 11. For simpler
queries it is usually best to use the
deterministic, exhaustive planner. deterministic, exhaustive planner.
</para> </para>
</listitem> </listitem>