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OPTIMIZER_MAX_PERMUTATIONS(转)

原创 Linux操作系统 作者:tochar 时间:2007-07-27 00:00:00 0 删除 编辑

OPTIMIZER_MAX_PERMUTATIONS

Parameter type

Integer

Default value

If OPTIMIZER_FEATURES_ENABLE is set to 9.0.0 or higher, then 2000

If OPTIMIZER_FEATURES_ENABLE is set to 8.1.7 or lower, then 80000

Parameter class

Dynamic: ALTER SESSION

Range of values

4 to 80000

OPTIMIZER_MAX_PERMUTATIONS restricts the number of permutations of the tables the optimizer will consider in queries with joins. Such a restriction ensures that the parse time for the query stays within acceptable limits. However, a slight risk exists that the optimizer will overlook a good plan it would otherwise have found.

The default value for this parameter is 80000, which corresponds to no limitation at all. Setting this parameter to a value less than 1000 normally ensures parse times of a few seconds or less.


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