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Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/runtime.sgml | 32 |
1 files changed, 20 insertions, 12 deletions
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml index f81c920d26d..ad4a6f98456 100644 --- a/doc/src/sgml/runtime.sgml +++ b/doc/src/sgml/runtime.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.231 2004/01/21 23:33:34 tgl Exp $ +$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.232 2004/01/23 23:54:20 tgl Exp $ --> <Chapter Id="runtime"> @@ -1396,7 +1396,7 @@ SET ENABLE_SEQSCAN TO OFF; Use genetic query optimization to plan queries with at least this many <literal>FROM</> items involved. (Note that an outer <literal>JOIN</> construct counts as only one <literal>FROM</> - item.) The default is 11. For simpler queries it is usually best + item.) The default is 12. For simpler queries it is usually best to use the deterministic, exhaustive planner, but for queries with many tables the deterministic planner takes too long. </para> @@ -1404,25 +1404,33 @@ SET ENABLE_SEQSCAN TO OFF; </varlistentry> <varlistentry> + <term><varname>geqo_effort</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 - 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 used. + algorithm. The recommended one to modify is + <varname>geqo_effort</varname>, which can range from 1 to 10 with + a default of 5. Larger values increase the time spent in planning + but make it more likely that a good plan will be found. + <varname>geqo_effort</varname> doesn't actually do anything directly, + it is just used to compute the default values for the other + parameters. If you prefer, you can set the other parameters by hand + instead. + The pool size is the number of individuals in the genetic population. + It must be at least two, and useful values are typically 100 to 1000. + If it is set to zero (the default setting) then a suitable default + is chosen based on <varname>geqo_effort</varname> and the number of + tables in the query. 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. + It must be at least one, and useful values are in the same range + as the pool size. + If it is set to zero (the default setting) then a suitable default + is chosen based on the pool size. 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. |