- Various tuning parameters for the genetic query optimization
- 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.
- 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.
- The selection bias is the selective pressure within the
- population. Values can be from 1.50 to 2.00; the latter is the
- default.
+ Controls the selection bias used by GEQO. The selection bias
+ is the selective pressure within the population. Values can be
+ from 1.50 to 2.00; the latter is the default.